They are used, in particular, when setting up antennas. However, the classic versions of GIR are focused on inductive coupling with the measured oscillating circuit. Their small inductors in most cases do not allow for sufficient coupling with antenna elements, for example, with a wire frame. As a result, the indication of the element's resonant frequency becomes unclear, which leads to significant measurement errors.

English shortwave operator Peter Dodd (G3LDO) solved this problem simply by making a simple specialized GIR to configure the elements of his “double square”. It differs from the classic versions of this device only in its design (Peter Dodd. Antennas. - RadCom, 2008, March, p. 66,67).

Rice. 1 GIR for tuning wire antennas

The circuit design of a heterodyne resonance indicator can be anything - a great many of them have been published in amateur radio literature. Peter Dodd used one of the simplest versions of GIR. Its diagram is shown in Fig. 1. Indication of resonance is carried out in it by changes in the source current of transistor VT1, and to make these changes more pronounced, a bias voltage is applied to the PA1 measuring device. It can be adjusted with a variable resistor R4 by setting the instrument needle close to the end mark of its scale before starting measurements. The resonance frequency is recorded with a digital frequency meter. Of the domestic transistors in this GIR, you can use, for example, KP303V transistors. The frequency meter is connected to connector XW1.

Rice. 2 Photo of the device

The design difference from traditional versions of the GIR is that the author used a large coil, which made it possible to provide a noticeable connection with the antenna element, the resonant frequency of which must be measured (with a frame or a linear vibrator). The appearance of his device is shown in Fig. 2. Its base is a dielectric plate 150 mm wide and 15 mm thick. Its length is not critical - it depends on the size of the box in which the GIR elements are placed, and on the size of the frequency meter. The author used a factory-made frequency meter. At the top of this plate there is a coil wound, which contains five turns of wire with a diameter of 1 mm in insulation. Its inductance turned out to be about 3 μH, which ensured that the GIR overlapped with the used KPI from 12 to 22 MHz. By changing the number of turns, you can obtain another frequency overlap required for tuning a specific antenna. In the upper part of the plate there are two dielectric hooks (of those used for fastening electrical wiring), with which the device is suspended on the wire element of the antenna. This allows you to fix the relative position of the GIR coil and this element, which also increases the accuracy of measurements. Part of the antenna wire element will be parallel to the long side of the rectangular turns of the coil. This, as the test has shown, ensures a fairly strong connection between the GIR coil and the antenna element and reliable registration of its resonant frequency. Thus, when working with “double square” frames, the change in the readings of the measuring device at resonance was approximately 40% of the entire scale.

Basic antenna parameters.
1. Resonant frequency.
2. Antenna impedance.
3. Directional pattern.
4. Gain.
5. K.S.V.

Let us give a brief description of the main parameters of the antenna.

Resonant frequency. An antenna emits electromagnetic waves when an exciting oscillation is applied to it. The efficiency of its radiation is greatest when the frequency of the exciting vibration coincides with the resonant frequency. Typically, the antenna length is equal to half or a quarter of the wavelength at the center operating frequency. However, due to capacitive and tip effects, the electrical length of the antenna is greater than its physical length. The resonant frequency of the antenna is affected by: the proximity of the antenna above the ground or some conductive object. If this is a multi-element antenna, then the resonant frequency of the active element can change in one direction or another, depending on the distance of the active element in relation to the reflector or director.
Antenna impedance. The impedance of an antenna varies along its length. The point of maximum current and minimum voltage corresponds to the lowest impedance and is called the excitation point. The impedance at this point is called the input impedance and it consists of the active radiation resistance of the antenna and the reactive component. At resonance, the reactive component of the input impedance must be zero. At frequencies above resonant impedance is inductive in nature, and at frequencies below resonant it is capacitive in nature. In practice, the reactive component of the impedance varies from zero to + 100 ohms. The impedance of an antenna also depends on other factors, such as its proximity to the Earth's surface or conductive surfaces. In an ideal case, a half-wave symmetrical vibrator has a radiation resistance of 73 ohms, and a quarter-wave asymmetrical vibrator has 53 ohms. In practice, these resistances vary from 5 to 120 Ohms for a half-wave antenna and from 5 to 80 Ohms for a quarter-wave antenna. The antenna resistance can be measured using a measuring bridge. Typically, a Wheatstone bridge, also called an antennascope, is used for this. Its design is simple and is described in various publications for radio amateurs. The measurement is carried out after tuning the antenna to resonance. It is customary to measure the antenna impedance over the entire operating frequency range to take into account the presence of reactivity at the edges of the range.
Antenna radiation pattern. Transmitting antenna radiation pattern
You can remove it by turning it and measuring the field strength at a fixed point at the transmission frequency. These measurements give the radiation pattern in polar coordinates.
The polar diagram shows the direction in which the antenna's energy is concentrated.
In amateur radio practice, this is the most difficult type of measurement. When carrying out measurements in the near zone, it is necessary to take into account a number of factors affecting the reliability of measurements. Any antenna, in addition to the main lobe, also has a number of side lobes; in the short wave range, we cannot raise the antenna to a greater height. The greatest energy comes from the transmitting to the receiving antenna if the first Fresnel zone is free from foreign objects. When measuring the radiation pattern in the HF range, the side lobe reflected from the Earth or from a nearby building can hit the measuring probe, both in phase and in antiphase, which will lead to measurement error.
Several control measurements will be required, measuring the distance to the measuring probe and measuring the height of the probe installation. This error also occurs when measuring on long-distance routes. The optimal angle of arrival of radio waves from the correspondent depends on the state of the troposphere and the number of reflections. This leads to the fact that different correspondents, depending on the route, will give different figures when estimating the F/B ratio. In connection with the above, it is advisable to place zones at the same height as the antenna and select the distance from the antenna to the measuring probe from 1.5 up to 2
Gain. If an antenna radiates the same power in all directions, it is called an isotropic or mathematical model, usually in practice the gain is expressed in decibels relative to a reference dipole. However, it is important that the reference and test antennas are measured under identical conditions. This means the same height of the suspension above the Earth and the same distance to the measuring probe, while the distance between the two being measured is close due to the influence of the antennas on each other. If a dipole is placed near a wave channel antenna at a close distance,
Then we get an in-phase array with one passive and one active antenna. The radiation pattern of both antennas will change and this will affect the half-wave dipole to a greater extent; its gain will be greater than that of a conventional single-standing dipole.
To avoid this error, first measure the
Half-wave dipole, and then remove it, install a new test antenna in its place and take another measurement.
K.S.V. Standing wave ratio. As you can see, this parameter comes in last place and is not paramount. If the antenna is tuned to resonance and during tuning we compensated for its reactivity and matched it with the power feeder in terms of resistance, K.S.V. will be one. Any antenna, simple or complex, is a resonant device and requires tuning. Tuning includes measuring the main parameters of the antenna and correcting them by adjusting the linear dimensions of the antenna elements, the distances between the elements, and adjusting matching and balun devices. Since we do not calculate the antenna ourselves, but take the dimensions of a ready-made design tested in practice, the question arises about the feasibility of tuning the antennas. As was already said above, the antenna is a resonant device, and since any resonant device requires tuning when repeated, the same rules apply to the antenna. Imagine that we need to calculate a parallel circuit for a specific frequency, no matter what formulas we use, no matter what programs we use, we can practically obtain the desired frequency only after adjusting the circuit in a ready-made generator design. It is not possible to calculate the influence of screens, parasitic capacitances and installation inductances, and so on. The same thing happens with the antenna, the edge effect of the building on which the antenna is located, the influence of the mast guys, etc., there are a lot of unknown quantities. And even all of the above is not an argument, just think, we achieved an increase in antenna gain of half a decibel or a decibel, can this really be assessed when working on the air, it turns out it is possible. After all, an antenna is characterized not by one specific parameter, but by the combination of all the main parameters, which include: gain, radiation pattern, efficiency. Here we should give an example that is known to many radio amateurs. When moving from simple antennas to more complex ones, the real increase in signal strength is much greater than when comparing the numerical gain values ​​of a simple and more complex antenna. For example, if a simple half-wave dipole antenna is compared with a double square antenna, then even an untuned double square with a gain of, for example, 5 decibels on the air can give an increase in signal strength from 10 to 30 decibels compared to a half-wave dipole, depending on the state of the air , transmission, angle of arrival of the signal, presence of industrial interference, etc. We could observe exactly the same effect by comparing two identical antennas, one of which was configured according to all the main parameters, the second was assembled according to the calculated values. And since the majority of radio amateurs tune antennas only according to KSV, hence the miracles on the air, some praise the same antenna design, while others are not happy with it. If you tune the antenna only according to S.S.V., then with the main parameters you will be lucky, but by going to the extreme and tuning the antenna only according to K.S.V., you can use the antenna to make a good matched load for the output stage of the transmitter. It will work well in normal mode, only the antenna may have a poor radiation pattern, low efficiency, part of the power will be spent on heating the antenna elements and the antenna-feeder path, and the most unpleasant thing that can happen to a radio amateur is television interference.
It follows from this that it is necessary to carry out measurements and adjustments of both the antenna itself and its individual components included in the antenna-feeder path, such as baluns and matching devices. When manufacturing and developing components and parts of a future antenna, provide for the possibility of measuring linear dimensions, where this is necessary to adjust individual elements of the antenna, taking into account the fact that the antenna must be adjusted at the altitude of its constant operation. Possibility of repeated lowering and raising of the antenna or remote adjustment.
Based on the fact that the majority of radio amateurs do not have a good base of specialized instruments, we will determine the minimum of simple and home-made instruments necessary for measuring the basic parameters of the antenna. The instruments are presented in the order in which measurements should be taken, and no other order of measurements is allowed during setup.
G.I.R. Heterodyne resonance indicator is a device for determining the resonant frequency of antenna elements. This is a simple generator assembled using a capacitive or inductive three-point circuit complemented by a detector and a DC amplifier. A pointer device is usually used as an indicator. It is desirable that the generator has electronic frequency tuning, for example using a varicap. The generator is compactly mounted in a small dielectric box. The generator is attached to the antenna element being measured through a dielectric, or is brought to the antenna element on a dielectric rod. There are no high demands on the stability of the generator, since the measurement time is not long. The resonant frequency of the active element of the antenna is measured with the antenna power cable disconnected. If it is a symmetrical vibrator or frame, then a short-circuit is made at the cable connection point or a constant resistance is installed, the value of which corresponds to the resistance of the active element of the antenna. There are 4 wires going down from the generator that supply: supply voltage, voltage to control the varicap and voltage is removed from the DC amplifier, the fourth wire is common. In the hands of the operator is an additional remote control that contains: power for the generator, a variable resistor for controlling the varicap and a microammeter. The frequency of the generator is controlled by an auxiliary receiver, which is located nearby. This measurement is best done together. One operator controls the frequency of the GIR generator and monitors the readings of the pointer instrument, the second operator controls the frequency of the GIR using the receiver. When tuning, when the frequency of the GIR generator coincides with the resonant frequency of the antenna element being measured, the dial gauge will show the voltage drop. Using the receiver, we determine the frequency of the GIR generator. This is the most accurate method for determining the resonant frequency of an antenna. Sometimes the GIR generator is connected to the active element of the antenna via an antenna power cable. The cable must be a multiple of half a wave for a given frequency. This method requires accurate measurement of the electrical length of the cable, the measurement error increases, and the measurement range narrows. By adjusting the active element of the antenna to resonance,
(by measuring its length or perimeter, if it is a frame) we move on to measuring the input resistance of the active element of the antenna at this resonance frequency. The antenna input impedance is measured using a high-frequency bridge. It can also be a homemade, simple device that can be manufactured even for a novice radio amateur. HF bridge circuits have been repeatedly published in the literature for radio amateurs. Take the simplest scheme. Even if this simple HF bridge does not even show the nature of the reactivity, simply by rotating the variable resistor we find a voltage dip; if the instrument needle does not drop to zero, this indicates that there is something in the antenna
there is some reactivity of a capacitive or inductive nature.
This reactivity is eliminated by introducing capacitance or inductance at the point where the antenna is connected to the RK cable, depending on the nature of the reactivity (the reactivity can be capacitive or inductive), selecting their value until the reactive component is eliminated. Since amateur radio bands are narrow, it is convenient to compensate for the reactive component not with discrete elements, but with a short-circuited loop, or a narrow-band balun, this is described in detail in the magazine
, Radio Design, No. 13. When manufacturing an HF bridge, the main condition is that you need to solder the circuit part by part, with leads from the elements having a minimum length. The circuit should be compact, let the connectors and the variable resistor be located in different planes, do not try to make a large and beautiful device. It is advisable to use resistors without induction; if it is not possible to get resistors without induction, instead of one resistor, place 3 - 4 resistors in parallel, this will reduce the inductance of simple resistors. In low-frequency ranges, below 10 MHz, you can use any resistors except wire-wound ones. Any microammeter with a detector can be used as an indicator of field strength. The only condition is that the indicator antenna (dipole or pin) must be much less than a quarter of the wavelength of the measured range.
The main thing is to learn how to use the devices. Practice shows that even with simple homemade devices you can fine-tune the antenna according to all the main parameters.

(GIR) is a universal measuring device. With its help, high-frequency cascades of receivers and radio stations are tuned and the frequencies of oscillatory circuits, capacitance of capacitors and inductance of coils are measured, and a number of other measurements are made.

Rice. 31. Circuit of a heterodyne resonance meter.

The GIR diagram is shown in Fig. 31. The device is a high-frequency generator assembled according to a three-point circuit on lamp L1. Changes in the grid current of the lamp are recorded with a microammeter. The device is powered from a half-wave diode rectifier of alternating mains voltage.

The principle of using the device is to note, during any measurement, at what frequency resonance occurs, characterized by a sharp drop in the grid current of the lamp. If you apply a small voltage to the anode of the GIR lamp so that the generator is not excited, and then bring the GIR coil to the circuit of the operating transmitter, then during resonance the device will give higher readings. The device has six replaceable coils designed for frequencies from 1.5 to 150 MHz.

The GIR generator is mounted in a separate metal case and connected to the rectifier with a three-core shielded wire 50 cm long (Fig. 32). The microammeter is located on the front panel of the rectifier housing.

Rice. 32. Appearance of a heterodyne resonance meter.

The generator must be installed with short conductors, otherwise it will be difficult to tune the device to a frequency of 150 MHz. The lamp is placed near the block to turn on the replaceable coils. All wires and capacitors going to ground are connected to the housing at one point.

Details. Tpi power transformer from any class 3 tube radio. It is only important that its filament winding is 6.3 V and the step-up winding is 150-200 V.

Winding data of coils L1—L5 are given in table. 2. The frames of the coils are rods made of insulating material - textolite, ebonite, organic glass.

Coil L6 (Fig. 32), designed for the frequency range 80-150 MHz, frameless. It is an open, elongated loop 45 mm high made of MG wire with a diameter of 2 mm. The tap is made at a distance of 30 mm from the grounded end.

The leads and taps of the coils are soldered to the pins of the octal bases of the radio tubes. An eight-pin porcelain socket is used to connect the coils to the generator. To calibrate the device, you need standard high-frequency signal generators of the GSS-6 and GVM types.

When any coil is connected to the GIR generator panel, the microammeter needle deflects. Resistor R2 sets the instrument needle to the middle position of the instrument scale.

Setting up the GIR begins with coil L1. The frequency of the GSS is set to about 2 MHz, the output voltage is maximum. A coil containing 8 turns of PEL 0.5 wire is connected to the output terminals of the GSS. The diameter of the coil must be such that it can be freely placed on the frame of the GIR coil. The resistor R2 slider is set to a position in which the GIR does not generate. The GSS coil is placed on the GIR coil L4 and the capacitor C1 is used to achieve the maximum deflection of the instrument needle - the setting indicator. Then check the frequency range covered by the GIR with this coil (for L1 1.55-3.5 MHz), If the frequency range differs significantly from that indicated in the table. 2, then the coil data is slightly changed to set the desired frequency range.

If the indicator arrow does not deviate and, therefore, it is impossible to determine the resonant frequency of the GSM, then turn on the phones in the sockets: when you tune the GSM circuit to resonance with the GSS frequency, modulation of the GSS will be heard in the phones.

This is how all GIR coils are configured. Since the GSS is designed for frequencies up to 26 MHz; then coils L5 and L6 are tuned using a meter wave generator.

The frequency scales of the first three ranges (coils L1-L3) are drawn on one half of the disk on the body of the GIR generator, and the scales of the other three ranges (coils L4-L6) are drawn on the second half of the disk. The scale needle is made of organic glass, 12 mm wide and the length of the entire scale. In the middle, the arrows are marked with a mark, which is filled with black ink. The arrow is placed on the axis of the variable capacitor and the frequencies are counted according to the risk.

Measurements using a heterodyne resonance meter

Measurements using GIR are mainly reduced to comparing the resonant frequencies of electrical circuits. To make certain measurements, a coil of the appropriate frequency range is inserted into the GIR (sometimes several coils are replaced when the frequency of the circuit being measured is unknown) and inductively coupled with the coil of the circuit under study. While observing the GIR dial indicator, rotate the handle of the variable capacitor, achieving frequency resonance. Resonance is detected by a sharp decrease in the readings of the dial indicator.

The nature of the change in the indicator readings depends on the quality factor of the coil and the degree of connection of the measured circuit with the GIR coil: the higher the quality factor of the circuit, the more significant the changes in the indicator readings.

Measuring the coupling coefficient between two coils. Using GIR, you can quite accurately measure the coupling coefficient between inductors. They do it like this (Fig. 38). A capacitor with a capacity of 20-100 pF is connected to one of these coils, preferably the coil with the highest inductance L1, and the resonant frequency of the resulting circuit is measured twice - with the second coil L2 open and when it is closed with a short piece of wire. Accordingly, two frequencies are obtained; f1 and f2. The coupling coefficient between the coils is determined by the formula

Rice. 33. Circuit for measuring the coupling coefficient between inductors.

This method can measure coupling coefficients from 0.1 to 0.7. A smaller coupling coefficient is difficult to measure, since the difference between the frequencies ft and f2 is small. When the coefficient is more than 0.7, due to the shunting effect of the second coil, the quality factor of the measured coil decreases, and it is difficult to accurately determine the frequency resonance.

Determination of the frequency of the RF generator.

To determine the frequency of the generator, including the auxiliary local oscillator of the receiver, use a variable resistor (in Fig. 31-R2) to disrupt the generation of the GIR, bring its coil to the coil of the generator under study and, by changing the capacitance of the tuning capacitor and the resistance of the variable resistor, achieve the greatest deflection of the instrument needle GIR. The generation frequency is determined by the scale of the variable capacitor GIR at the moment of resonance. In this case, the connection between the GIR coil and the generator is weakened to a minimum: the smaller this connection, the more accurately the generation frequency will be determined.

The frequency of a generator whose power exceeds 1 W must be measured very carefully so as not to damage the GIR device due to the large current through it. In this case, it is enough to bring the GIR coil to the generator coil no closer than 20-40 mm. As the GIR is tuned into resonance with the frequency of the generator, it is gradually moved further away from the generator coil. This prevents damage to the device and provides a more accurate frequency reading.

Measuring coil inductance. To measure the inductance of a coil, a capacitor whose capacitance is known is connected to it, and the resonant frequency of the resulting circuit is measured using a GIR. The inductance of the coil is determined by the formula

where L is the measured inductance, mgn; C is the known capacitance of the capacitor, pf; f is the resonant frequency of the circuit, MHz.

To measure the inductance of a coil with a large number of turns, the capacitance of the capacitor connected to it must be 150 ~ 300 pF. When measuring the inductances of VHF coils, its capacitance should be 25-30 pF. To simplify the calculation of the inductance of the coils in the medium and long wave ranges, a capacitor with a capacity of 100 pF is connected to them.

The capacitance of a capacitor is measured using a reference coil whose inductance is known. The inductance of this coil can be from 10 to 200 milliseconds. The measurement technique is the same as when measuring the inductance of a coil, with the only difference being that the standard is not capacitance, but inductance. Noting the resonance point, determine the capacitance of the capacitor using the same formula, only the capacitance and inductance are swapped:

where C is the measured capacitance, pf; L - coil inductance, μH f - resonant frequency, MHz.

This method can measure capacitances of capacitors from 10 to 1500 pF.

Tuning an antenna using GIR involves measuring its resonant frequency. To do this, use inductive (Fig. 34) or capacitive (Fig. 35) coupling of the GIR with the antenna. The choice of the location of the connection between the GIR and the antenna and the type of connection (capacitive or inductive) are important when measuring the resonant frequency of the antenna. To accurately measure the resonant frequency of an antenna, you need to know at least approximately the frequency at which the antenna will operate. The coupling coefficient must be greater than when determining the resonant frequency of the circuit. The connection between the antenna and the GIR should be especially strong at frequencies less than 10 MHz.

If the antenna length is more than half the wavelength, then capacitive coupling is used (through a capacitor with a capacity of 5-15 pF). When the antenna length is less than half a wave, inductive coupling is used. When tuning half-wave vibrators, the cut point of the vibrator is connected with a wire so that a connection loop is formed (Fig. 36), which is brought to the GIR when tuning.

Using GIR, you can match the antenna with the cable, and the cable with the transmitter output. There is a rule: if the antenna is correctly matched with the cable and with the transmitter, the resonant frequency of the antenna should not change when the cable is connected to it. Therefore, by changing the connection between the cable and the transmitter and the dimensions of the balun elements, it is ensured that the GIR frequency remains almost unchanged when the antenna is disconnected from the cable or the cable from the transmitter.

When measuring the resonant frequency of feeders (cables) with low characteristic impedance, it is taken into account that their inductance is very small (fractions of a microhenry), so the determination of resonant frequencies is carried out carefully.

V.V. Voznyuk. To help the school radio club

Key tags: radio tubes, Voznyuk, Measurements

The article was written for beginners, those who are going to set up an antenna for the first time to work on the channel (frequency) they need. Those who have already repeatedly tuned antennas are unlikely to find anything useful for themselves in the article.
The article describes the main points of setting up simple single-band antennas - automotive mortise ones, on a magnetic base, basic 1/4 GP, 1/2 (half-wave), 5/8 (five-eighths).

What you need to set up your antenna

SWR meter
A device that shows the ratio of the forward (coming from the radio station to the antenna) and backward (reflecting from the antenna) waves in the cable.
Indirectly, this device shows that the output impedance of the radio station is equal to the resistance of the cable, and it is equal to the resistance of the antenna. You can read about what characteristic impedance is and how it differs from that shown by a regular tester in the article:.
An SWR meter (SWR meter) can be purchased (the price is about 1000 rubles) or you can borrow it from someone you know who has one.

Radio station
The SWR meter does not work without a radio station.
The more “grids” there are in a radio station, the wider the frequency range the radio station can tune in, the easier it will be to tune the antenna to the desired frequency (channel).
Having a radio station with 40 channels at 27 MHz, it is possible to configure the antenna, but it is very difficult; with a radio station that has 400 or 600 channels, this is much easier.

Tape measure or ruler
It will be needed to measure the antenna surface and determine how many centimeters to shorten or lengthen.
In principle, you can do without a tape measure or ruler and simply perform the adjustment step by step, slightly shortening or lengthening the antenna blade.

Basic principles when setting up an antenna

The antenna needs to be adjusted to the place where it will then be located.
That is, the antenna needs to be configured in the conditions in which it will continue to be used, especially if there are some people at a distance closer than 2-3 wavelengths (wavelength = 300/frequency in MHz (for 27 MHz wavelength is approximately 11 meters)) conductive objects parallel to the antenna surface.
If this is a basic antenna, then you already need to prepare a mast for it, which allows you to remove and install the antenna, raise and lower it all for configuration and maintenance.
If this is a car antenna, then the car should be parked so that nearby there would be exactly the same situation that would exist when driving it at the time the radio station is working, that is, at a distance of about 5-10 meters there were other cars, but on the other side there should not be be the walls of reinforced concrete houses, garages, you cannot stand inside an iron garage or hangar. At the time of measurements during setup, the car's doors and trunk must be closed. You should not stand next to the car yourself; the human body absorbs radio waves and thereby introduces losses and affects the operation of the antenna.
There should be no moving conductive objects at a distance of 2-3 wavelengths from the antenna.
All connections of devices must be reliable.
You should not hold everything “in weight”, using your hands to press roughly stripped pieces of cable that are about to fall out of the connectors or are short-circuited to the contacts.
Reliable connections are needed so that the readings of the device do not change as they please, do not float and are repeatable. If the readings are not repeatable, then these are no longer instrument readings, but the weather on Mars at the time of eating Snickers, and it is impossible to rely on such readings.

How to use an SWR meter

We connect the cable to the antenna, the other end of the cable to the SWR meter, to the “ANT” connector, connect the SWR meter “TRANS” connector to the antenna connector of the radio station.
We turn on the radio station and set the frequency at which we will measure the SWR.
If there is an SWR/PWR switch, move it to the SWR position.
Switch on the SWR meter "FWD/REF" to the FWD position.
We press on the transmission on the radio station and set the arrow protruding from the SWR meter to the end of the scale. Let's release the transmission.
Set the "FWD/REF" switch to the REF position.
We press the gear and count the SWR reading on the indicator. On most SWR meters, the less the needle deviates, the less SWR, if it does not deviate at all, then SWR = 1 or the device is dead. If at all frequencies, in the REF position, the arrow does not deviate, then either you have a good equivalent load connected instead of an antenna, or the device is dead, but let’s not talk about sad things.

Antenna setup - step by step

We connect everything to measure the SWR, as mentioned above, the antenna in the working position.
- We set the radio station to the highest frequency that the radio station is capable of producing, for example grid G ​​channel 40 (more precisely, see the instructions for the radio station).
- We measure the SWR, moving down the frequencies through about 20 channels (200 kHz), remember at which frequency (channel, grid) the SWR was minimum and which SWR was at the minimum.

Now there are several options:
The SWR is large everywhere, the device is off scale.
Either you are using the SWR meter incorrectly or you have a break in the cable or antenna.

The SWR drops smoothly as the frequency decreases, but we have not reached the minimum.
Your antenna is too long. It needs to be shortened. When it comes to shortening, it’s worth remembering the golden rule: “measure twice, cut once.” In most cases it is impossible to stick the shortened one back, so we shorten it a little bit, for CB antennas in the 27 MHz range a little bit is about 1 centimeter, for LPD or PMR antennas in the 433-446 MHz range a little bit is 2 millimeters.

SWR increases as the frequency decreases.
Your antenna is too short. The antenna needs to be extended. How much exactly - it’s better to do it by 20 percent, and then shorten it.

The SWR fell as the frequency decreased, at a certain frequency it became minimal, and then, as the frequency decreased further, it began to increase again.
This is the most common case.
This behavior means that everything is normal, the antenna is operating in the desired range, all that remains is to adjust it to the desired frequency (channel).
If you have this case, then it is advisable to find exactly on which channel the minimum SWR is.

If the frequency at which the minimum SWR was lower than the one you need, then the antenna needs to be shortened a little, literally 5 millimeters at a time, if we are talking about the 27 MHz range, after each shortening, look where the minimum SWR is now, and shorten it until the minimum The SWR will not be at the frequency you want.

If the frequency at which the minimum SWR was higher than what you need, then the antenna needs to be lengthened.

What to do if the minimum SWR is at the desired frequency, but this minimum value is still high

This indicates that the antenna does not work exactly as intended by the manufacturer or the antenna is rubbish, but there is no need to immediately talk about sad things.
If this is a car mount antenna, then it may “not have enough mass,” that is, the contact with the ground is poor.
If this is a car antenna on a magnet, then it may also “not have enough mass”, for example the paint layer is too thick.
Or your car antenna is located where it should not be placed - next to the elements of the metal roof rack, next to the additional light that you hung on the trunk, you even magnetized it to the hood or trunk, bumper or wheel rim.
Maybe you mounted a mortise-in antenna on the aluminum runners of the roof rack that you have on the roof, but the rack turned out to be plastic, not aluminum, or does not have reliable contact with the ground of the car, or is not long and wide enough to act as a mass for the antenna.

If the antenna is on a magnetic base, try looking for another place to “slap” it, try from the corner of the roof, in the center of the roof, from another corner.
Radio frequency currents do not flow exactly like direct current, where the tester shows excellent contact, for radio frequency this may turn out to be a “bottleneck”.

If the antenna is mortise-mounted, check to see if you have thoroughly cleaned the paint from the area where the antenna ground contact is attached.
If you mounted the embedded antenna on the trunk or some kind of fastener on the drain, try to improve the contact with ground. There were cases when the author of the article took 2 pieces of wire 0.5 mm thick without insulation, wound them around a bracket on which a mortise antenna hanging on a drain or trunk was attached, threw them into different corners of the car roof along the drains and the SWR decreased from 3 to 1, then the antenna began to work perfectly (naturally, the signal on the air also improved).
Throw in additional wires, tear off the paint and then pour sealant, or look for other ways to improve the mass or installation point - it’s up to you, it’s your antenna and your car.

If you do not have a car antenna, but a basic version, then the treatment here is exactly the same, namely: maybe you need more “mass”, or maybe you need to get into the antenna design with a soldering iron.
To begin with, we make sure that there is enough mass - the base pipe, which is also the main counterweight, the mass for antennas of the 5/8 (five-eighths) and 1/2 (half-wave) types should be at least 1/4 of the wavelength, that is, for 27 MHz it is about 2 meters 75 centimeters. More is better; less - you will have to extend it with a wire thrown along the roof.
Although sometimes it happens that everything is done well, but the antenna is not tuned, this happened to a friend of the author of the article, 1/2 did not want to tune in. It seems to be in frequency, but the SWR is not 1 or even 1.2 or 1.5 - it turned out that someone “got into the antenna” before him and cut off a turn of the coil installed inside the antenna.
It is also very likely that the nearby stretched optics of your provider or the mast of a collective antenna are interfering with your base antenna.

How much to cut and what is the ruler for?
Antenna sizes depend linearly on frequency.
If the antenna is full-size, then how much it needs to be shortened or lengthened to get to the desired frequency directly depends on the ratio of the current frequency where it resonates and the desired frequency where you would like the antenna to resonate.
Let me explain with an example:
we have a quarter, its length may be 267 centimeters, it resonates (the SWR is minimal) turned out to be at a frequency of 27.0 MHz (channel 4, section C), we want the antenna to work at 27.275 MHz.
We count K frequency differences:
27.0 / 27.275 = 0.9899175068744271
We multiply the current antenna length by this K:
267 * 0.9899175068744271 = 264.3
and we get the length that the antenna must have to earn 27.275.
Calculate how much to cut:
267 - 264 = 3 cm.
However!
There is no need to cut exactly 3 cm right away. Don’t forget, an antenna is not only a rod, it’s also counterweights. Everything has an impact.
This way you can determine the order of the first cutting - either 3 cm or 5 mm.
Next we proceed step by step.
For the example above, you can cut off 1.5 cm, again find the resonance, and based on the result obtained, move on.

Lastly, although this probably should have been written first:
Basic rules for installing antennas
The antenna must be placed no closer than the same wavelength to other conductive objects, especially those that will be parallel to the antenna.
The higher the antenna is installed, the better.
It is clear that for car antennas at 27 MHz these rules are simply impossible to comply with, so car antennas are a compromise, so don’t demand miracles from them.

If you still have no time, no desire to understand the intricacies of SWR measurement, look for an SWR meter, configure the antenna yourself, and you are in Novosibirsk, you can contact, for example, here:

Setting up HF antennas

Tips for radio amateurs to achieve the best possible results with:

• setting up amateur radio antennas of various designs;
• antenna matching in amateur conditions;
• working with antenna analyzers;
• the use of matching devices (tuners);
• efforts to reduce television interference (TVI).

Part 1. Antennas and their settings

Part 2.

Part 3.

Part 1.

Antennas and their settings

An installed antenna usually needs to be adjusted before connecting it to the transceiver. The antenna is tuned to a given wave range. Its characteristic impedance is consistent with the characteristic impedance of the transmission line, and the transmission line is consistent with the output of the transceiver.

It happens that not all radio amateurs always understand the importance of good coordination of the “Transceiver - Transmission Line - Antenna” path; more precisely, they understand the importance, but are completely unable to really assess the state of affairs (for various reasons). Then you have to be content with the readings of the built-in SWR meter (preferably close to unit). The most unpleasant thing about this is that in case of poor coordination, the owner of the radio station simply begins to increase the power until everyone responds.

And how much power will be directed to the neighbor’s TV and will be used to heat up the atmosphere - one can only guess and have problems, with the neighbor that’s for sure.

The picture above schematically shows a circuit of three devices and two transitions between them.

The secret is that the SWR meter shows what it “sees” on the transceiver connector. The remaining devices and impedances are “hiding behind” those in front, like one nesting doll inside another. And at every transition and device there are losses due to attenuation in the cable or transmission line and poor SWR.

First, let's define the units of measurement. For specialists, for example in the field of agriculture, the term diBi is closer to the medical term than to the concept of “how many times”. Therefore, for starters, a table of losses in dB and a breakdown in percentages, which everyone understands well.

Looking at this, you can even easily agree that in a completely unfavorable situation, nothing will get into the antenna at all.

If the antenna has a real impedance equal to the resistance of the transmission line, be it a coaxial cable, a quarter-wave transformer or a tuned line, then the SWR meter at the transceiver connector will measure the real SWR of the antenna-feeder device (AFD). If not, the SWR meter will show a match with the cable rather than with the entire system.

Due to the fact that it is very inconvenient to measure SWR directly on an antenna already raised above the ground, tuned lines and quarter-wave or half-wave sections of cable are often used to communicate with the antenna, which are also transformers that accurately “transmit” the SWR value of the antenna to the radio input (impedance).

That is why, if the antenna resistance is unknown, or it is just being configured, it makes sense to use a coaxial cable of a certain length. The tables above will help you choose the lesser of two evils - either feeder losses or SWR losses. In any case, it is better to know what is described above than to remain ignorant.

When choosing, installing or configuring a particular antenna, you need to know several of their basic properties, which can be described in the following concepts.

Resonance frequency

An antenna emits or receives electromagnetic waves most efficiently only when the frequency of the exciting wave matches the resonant frequency of the antenna. It follows from this that its active element, vibrator or frame has such a physical size that a resonance is observed at the desired frequency.

By changing the linear dimensions of the active element - the emitter, the antenna is tuned to resonance. As a rule (based on the best efficiency/labor ratio and matching with the transmission line), the antenna length is equal to half or a quarter of the wavelength at the center operating frequency. However, due to capacitive and tip effects, the electrical length of the antenna is greater than its physical length.

The resonant frequency of the antenna is affected by: the proximity of the antenna above the ground or some conductive object. If this is a multi-element antenna, then the resonant frequency of the active element may also change in one direction or another depending on the distance of the active element in relation to the reflector or director.

Antenna reference books provide graphs or formulas for finding the shortening coefficient of a vibrator in free space depending on the ratio of the wavelength to the diameter of the vibrator.

In reality, it is quite difficult to determine the shortening coefficient more precisely, because The height of the antenna, surrounding objects, soil conductivity, etc. have a significant impact. In this regard, during the manufacture of the antenna, additional adjustment elements are used, which allow the linear dimensions of the elements to be changed within small limits. In a word, it is better to “bring” the antenna to working condition at its permanent location.

Typically, if the antenna is a wire dipole or Inverted V type, shorten (or lengthen) the wire connected to the central core of the feeder. So with smaller changes you can achieve a greater effect.

In this way, the antenna is tuned to the operating frequency. In addition, by changing the inclination of the beams in Inverted V, the SWR is adjusted to a minimum. But this may not be enough.

Impedance or input resistance (or radiation resistance)

The word impedance denotes the complex (total) resistance of the antenna and it varies along its length. The point of maximum current and minimum voltage corresponds to the lowest impedance and is called the excitation point. The impedance at this point is called the input impedance. The reactive component of the input impedance at the resonant frequency is theoretically zero. At frequencies above resonant, the impedance is inductive, and at frequencies below resonant, it is capacitive. In practice, the reactive component in most cases varies from 0 to +/-100 Ohms.

The antenna impedance may depend on other factors, for example, the proximity of the location to the Earth's surface or any conductive surfaces. In the ideal case, a symmetrical half-wave vibrator has a radiation resistance of 73 Ohms, and a quarter-wave asymmetrical vibrator (read pin) - 35 Ohms. In reality, the influence of the Earth or conductive surfaces can change these resistances from 50 to 100 ohms for a half-wave antenna and from 20 to 50 ohms for a quarter-wave antenna.

It is known that the Inverted V antenna, due to the influence of the earth and other objects, never turns out to be strictly symmetrical. And most often the radiation resistance of 50 Ohms is shifted from the middle. (One arm should be shortened and the other increased by the same amount.) So, for example, three counterweights slightly shorter than a quarter wave, located at an angle of 120 degrees in the horizontal and vertical planes, turn the GP resistance into a very convenient 50 Ohms for us. And as a rule, the antenna resistance is more often “adjusted” to the transmission line resistance than vice versa, although such options are also known. This parameter is very important when designing the antenna power unit.

Radio amateurs who are not very experienced in this matter do not even realize that not all active elements in multi-band antennas can be physically connected! For example, a very common design is when only two or even one element is connected directly to the feeder, and the rest are excited by re-radiation. There is even a word for it – “cross-pollination”. Of course, this is no better than direct excitation of vibrators, but it is very economical and greatly simplifies the design and weight. An example is numerous designs of tri-band antennas such as Yagi, Russian Yagi, including designs of the XL222, XL335 and XL347 line.

Active nutrition of all elements is a classic. Everything according to science, maximum bandwidth without blockages, much better than the radiation pattern and the Front/Back ratio. But everything good is always more expensive and heavier. Therefore, behind this there is a more powerful mast, the same turn, an area for guy wires, etc. and so on. For us, consumers, cost is not the last argument.

We should not forget about such a technique as symmetry. It is necessary to eliminate the “skew” when feeding a symmetrical antenna with an asymmetrical power line (in our case, a coaxial cable) and makes significant changes to the reactive component of the resistance, bringing it closer to a purely active one.

In practice, this is either a special transformer called a balun (balance-unbalance) or simply a number of ferrite rings placed on the cable near the antenna connection point.

Please note that when we say “balun-transformer”, we mean that in this case the impedance is actually transformed, and if it is just a balun, then it is more likely a choke included in the cable braid circuit.

Usually, even for a range of 80 meters, a dozen rings are enough (cable size, permeability something from 1000NN and less).

On higher ranges less is possible. If the cable is thin and there are one or more rings of large diameter, you can do the opposite, i.e. wind several turns of cable around the ring(s).

Important: of all the turns that fit, half must be wound in the other direction.

There is a practice of using 10 turns of cable on a 1000NN ring on an 80-meter dipole, and 20 rings on a cable on a tri-band hexabim (spider).

Their total resistance (as inductance) at the operating frequency must be more than one kOhm.

This will prevent the flow of current through the cable braid, thereby achieving symmetrical excitation at the connection point.

The most practical solution, which is used everywhere due to its simplicity and efficiency, is 6-10 turns of the power cable into a coil with a diameter of 200 mm (the turns should be fixed either on the frame or with plastic guides so that an inductance is obtained, and not a cable coil.

You can clearly see this in the photo below. This technique will work great on your regular dipole. Try it and immediately notice the difference in TVI (TV Interference) levels.

Gain

If an antenna radiates the same power in absolutely all directions, then it is called isotropic, i.e. directional pattern – sphere, ball. In reality, such an antenna does not exist, so it can also be called virtual. She only has one element and has no enhancement.

The concept of “amplification” can only be applied to multi-element antennas; it is formed due to the re-emission of in-phase electromagnetic waves and the addition of signals on the active element.

Everyone is familiar with the situation with poor mobile phone connections in rural areas. And her solution is to find a long conductive object and bring the “mobile” to it as close as possible. The quality of communication increases. Of course, due to the re-emission of base station signals by the conductive object we found.

Those who are older remember a similar situation with transistor radios of the 60s, listening to the Beatles on HF. Same situation. This was especially noticeable on magnetic antennas - due to the large number of turns of the magnetic antenna, the summed re-radiated voltage was greater.

A special case, sometimes the word “gain” is used in relation to a single pin to determine how much the vertical component of the radiation is less than the radiation in the horizontal plane. A priori, this is not an amplification - it is rather a transformation coefficient. Not to be confused with phased or collinear verticals: they have two or more elements and have real gain.

The gain can be obtained by concentrating the radiation energy in one direction. The amplification is formed by adding and subtracting radio waves excited in the vibrator and re-emitted by the director.

In the animated figure below, the resulting wave is shown in green.

Directional coefficient (DA) is a measure of the increase in power flow due to compression of the directional pattern in one direction. An antenna can have a high efficiency, but a low gain, if the ohmic losses in it are large and “eat up” the useful voltage obtained due to re-radiation.

Gain is calculated by comparing the voltage across the antenna being measured with the voltage across a reference half-wave dipole operating at the same frequency as the antenna being measured and at the same distance from the transmitter. Typically, gain is expressed in decibels relative to a reference dipole - dB. More precisely, it will be called dBd.

But if we compare it with a virtual, isotropic antenna, then the value will be expressed in dBi and the number itself will be slightly larger, because the dipole still has some directional properties - maximums in the direction perpendicular to the canvas, remember, but an isotropic antenna does not. The denominator has a smaller number, so the ratio is larger. But don’t be fooled by them, we are “practitioners” and always look at dBd.

Directional pattern

They try to design antennas in such a way that they have a maximum gain (receive and transmit) in a pre-selected direction. This property is called directivity. The figure shows a dynamic drawing of the addition and subtraction of radio waves excited in the vibrator and re-emitted by the reflector and director. The resulting radio wave is indicated in green.

The nature of the antenna radiation in space is described by the radiation pattern. In addition to radiation in the main (main) direction, there are side radiations - back and side lobes.

The radiation pattern of a transmitting antenna can be constructed by rotating it and measuring the field strength at a fixed distance without changing the transmitting frequency. These measurements, converted into graphical form, give an idea in which direction the antenna has maximum gain, i.e. The polar diagram shows the direction in which the energy emitted by the antenna is concentrated in the horizontal and vertical planes.

In amateur radio practice, this is the most difficult type of measurement. When carrying out measurements in the near zone, it is necessary to take into account a number of factors affecting the reliability of measurements. Any antenna, in addition to the main lobe, also has a number of side lobes; in the short wave range, we cannot raise the antenna to a greater height.

When measuring the radiation pattern in the HF range, the side lobe reflected from the ground or from a nearby building can hit the measuring probe, both in phase and in antiphase, which can lead to an error in the measurements.

Simple wire antennas also have a radiation pattern. For example, a dipole has a figure eight with deep dips in the diagram, which is not good. The same goes for the popular Inverted V antenna.

If everyone remembers textbooks on radio engineering or Rothhammel well, then an inverted vee (dipole) has a figure-of-eight diagram. Those. there are deep gaps. And if you change the position of the blades, swap one pair (move the blades of one antenna, for example, at an angle of 90 degrees), then the diagram begins to approach, so to speak, a thick sausage. But the most important thing is that the dips disappear, and the diagram is “rounded up”. With a dipole, it is enough to change the angle between the halves. And if we make this angle at the wave dipole equal to 90°, then with some stretch the radiation diagram can be called circular.

Bandwidth

As a rule, there are two classes of antennas: narrowband and broadband. It is very important that good matching and a given gain are maintained in the operating frequency range. The antenna bandwidth should not change when the transmitter or receiver changes frequency.

Narrowband antennas include all simple resonant antennas, as well as directional ones such as “wave channel” and “square”. As an avid telegraph operator, I am quite satisfied with antennas with a bandwidth of 100 kHz, but there are generalists who love SSB, so antenna manufacturers are trying to provide a bandwidth equal to the width of amateur radio sections. For example, a “wave channel” antenna for the amateur radio range of 14 MHz must have a bandwidth of at least 300 kHz (14000 - 14300 kHz) and, moreover, good matching in this frequency band.

Broadband antennas are distinguished by a large frequency range, in which the operating properties of the antenna are preserved, many times superior to resonant systems in this regard. These include log-periodic and helical antennas.

Efficiency factor (efficiency)

Part of the power supplied to the antenna is radiated into space, and the other part is converted into heat in the antenna conductors. Therefore, the antenna can be represented as an equivalent load resistance consisting of two parallel components: radiation resistance and loss resistance. The efficiency of an antenna is characterized by its efficiency or the ratio of the useful (radiated) power to the total power supplied to the antenna.

The greater the radiation resistance in relation to the loss resistance, the greater the KGID of the antenna. It is quite obvious that good electrical contacts and small ohmic resistances (thickness of the elements) are good.

As you can see, this parameter interests us last and is not the main one. (God forbid you think that you don’t have to worry about its bad value. If the SWR is more than two, this is bad). If the antenna is tuned to resonance and during the setup we compensated for its reactivity and matched it with the power feeder in terms of resistance, then the SWR will be equal to unity. Just do not use the device built into the transceiver as an SWR meter. It's more of an indicator. Plus, the autotuner does not always turn off. But we want to know the truth. 🙂 And don’t forget about symmetry (see above). It is known that it is possible to power antennas with a coaxial cable of any length, which is why it is an asymmetrical coaxial cable, but in the case when two antennas are powered via one cable, it is better to make sure that for both calculated frequencies the cable length is a multiple of a half-wave.

For example, for a frequency of 14.100, the cable length should be:

100 / 14.1 x 1; 2; 3; 4, etc. = 7.09m; 14.18m; 21.27m; 28.36m, etc.

For 21,100 MHz respectively:

100 / 21.1 x 1; 2; 3; 4, etc. = 4.74m; 9.48m; 14.22m; 18.96m; 23.70; 28.44, etc.

Usually people consider the minimum feeder length to be a priority, and if we calculate slightly longer lengths, we will see that for the 15 and 20 meter ranges the first “multiplicity” will occur with a cable length of 14.18 and 14.22 meters, the second, respectively, 28.44 meters and 28.36 meters. Those. the difference is 4 centimeters, the length of the PL259 connector. 🙂 We neglect this value and have one feeder for two antennas. Calculating the “multiple length” of the feeder for the 80 and 40 meter ranges will now not be difficult for you. If we have not forgotten about balancing, we can now tune the antenna with confidence that the feeder does not introduce any interference into the purity of the experiment. A very good option is two double Inverted Vs on two masts: 40 and 80 + 20 and 15 meters. With this option (well, also GP at 28 MHz in case there is a passage), the EN5R goes on almost all expeditions.

Well, now we are armed with theoretical knowledge about the properties of antennas and can adequately perceive advice on their implementation and configuration. Of course, everything is theoretical, because you know better on the spot. The most popular antenna among radio amateurs is the dipole. So, the initial conditions: we can raise and lower the dipole within half an hour and many times a day. Then, most likely, there is no point in wasting time on pre-setting it on the ground: this will not be difficult to do for it to work at gimbal height. From preliminary theoretical knowledge, you only need information that the operating frequency of a dipole near the ground will “go up” by 5-7% with an increase. For example, for the 20-meter range this is 200-300 kHz.

To tune into resonance with the operating frequency of a conventional dipole, you can use (in addition to the lower-cut-raise system) either a sweep generator (many know this device under the name GKCh), or a GIR, or, at worst, a GSS and an oscilloscope.

It is clear that if there are no such devices, then you will have to adjust the dipole blade to resonance using an ordinary field indicator, or as it is also called - a probe. This is an ordinary dipole with a length of blades no less than ten times less than the estimated length of the antenna itself, connected to a rectifier bridge (better on germanium diodes - it will respond to lower voltage), loaded on a regular pointer instrument - a microammeter with a maximum scale size (for better it was visible).

It would be better if the probe has a circuit (filter) for the operating frequency, so as not to tune in to your neighbor’s mobile phone, and with an amplifier. For example this one. It is clear that we adjust the length of the dipole to the maximum of its radiation at the operating frequency. The minimum SWR in this case should be formed automatically. If not, remember about symmetry. If it doesn’t help and the SWR value is still high, you’ll have to think about matching methods. Although this happens very rarely.

The next most complex composition is several dipoles over one cable. Well, read about the cable above, but about the canvases you should know the following: to minimize the influence of one on the other, they should be stretched at an angle of 90 degrees. If this is not possible, then after correcting the length of one, you will most likely have to adjust the other as well. Several inv V. on one cable - the option described above and differs only in that you can “trim” the SWR to the minimum value by adjusting the angle of inclination of the blades in the vertical (towards the mast), which, of course, is simpler than making a matching device and even simpler than another adjusting the length of the canvas.

So, it turns out that a sequence of actions must be performed - first the antenna is tuned to resonance, and then the minimum SWR is achieved in the required frequency band. All this is true for simple dipole antennas. And it becomes very complicated if the antenna is multi-element. In this option, you cannot do without special devices, since it is necessary to set up not only a system with several unknowns, but also to achieve well-defined directional properties.

Tuning includes measuring the main parameters of the antenna and correcting them by adjusting the linear dimensions of the antenna elements, the distances between the elements, and adjusting matching and balun devices. Advice: trust the experts. As the famous Belarusian shortwave operator Vladimir Prikhodko EW8AU said, “by tuning the antenna only by SWR, you can make a good matched load from the antenna for the output stage of the transmitter. It will work well in normal mode, only the antenna may have a poor radiation pattern, low efficiency, part of the power will be spent on heating the antenna elements and the antenna-feeder path, and the most unpleasant thing that can happen to a radio amateur is television interference.” .

Part 2.

Working with antenna analyzer MFJ-259, MFJ-269

The MFJ-259 analyzer is designed to operate in 50 ohm radio frequency (RF) circuits from 1.6 to 170 MHz. It consists of four main components - a high-frequency generator, a digital frequency meter with liquid crystal display (LCD display), a 50-ohm RF bridge and a bridge standing wave ratio meter (SWR meter). For ease of operation, the frequency range of the RF generator is divided into 6 subranges.

Using the analyzer, measurements become quite easy:

Antenna - SWR, resonant frequency, bandwidth, etc.

Antenna tuners - SWR, tuning frequency.

Radio frequency amplifiers - input, output impedance, bandwidth.

Coaxial lines - determine the shortening factor, SWR, turn, resonance

Symmetrical lines - characteristic impedance, shortening coefficient, resonances.

Matching and tuning of coaxial resonators - SWR, cutoff frequencies, bandwidth.

Filters - determine the resonant frequency, cutoff frequency, and passband.

Oscillatory circuits - determine the resonant frequency, bandwidth, quality factor.

Capacities of small capacitors.

Chokes and coils - inductance frequencies of series and parallel resonance and the magnitude of inductances.

Transmitters and generators - determine the frequency of transmission and generation.

Pre-setting of P-circuits.

The analyzer can be used as a signal generator.

The MFJ-259 and MFJ-269 devices are portable, can be powered either from an external power source 8 ... 18 V (max.) or from an internal power source (for example, 8 AA-series elements).

On the front panel of MFJ-259/269 are located (check “bottom”)

LCD display of a digital frequency meter, on the left is a dial indicator of the SWR meter, on the right is a dial indicator of the RF bridge, which by the way gives reliable readings only when an active load is connected (at SWR-1), since the device is designed to operate in 50-ohm circuits, then the rest (except 50 Ohm), the readings of the bridge indicator at an SWR other than 1 will indicate the presence of reactivity in the load measured at a given frequency and will not correspond to the printed values ​​on the bridge indicator scale, i.e. will be relative.

Below, on the front wall of the device, on the left there is a knob for adjusting the generator frequency, on the right there is a switch for generator subbands.

On the top wall (from left to right) there is a switch for the counting time of the device, under it a switch for operating modes of the device: measuring the frequency of the internal generator, measuring the frequency from the outside when the generator is turned on, the same when it is turned off, a BNC socket - the frequency meter input, an antenna input socket, a power switch and external power socket for the device (recessed inside, and when an external power source is connected, the internal one is turned off).

Having become familiar with the controls and displays of the device, we will decide what measurements and how we can make them.

Measuring standing warrior ratio - SWR

SWR is defined as the ratio of the load resistance (Rн) to the resistance of the current source (Ri) KCB= Rн/Ri

Since almost all the equipment used by radio amateurs is fifty-ohm, this device is designed for use in 50-ohm circuits.

When connecting a 150 Ohm active load to the antenna socket of the device, the result is SWR = 150/50 = 3. To get SWR = 1, you should connect a 50 Ohm load. You should not be misled that 25 Ohms of reactive and 25 Ohms of active resistance will give SWR = 1 when connected in series. This statement is absolutely false. The SWR will be equal to 2.6. You can't fool the device.

Another misconception is that by changing the length of the supply line you can change the SWR. If the line resistance is 50 Ohms, and the load resistance is 25 Ohms, then, regardless of the length of the supply line, SWR = 2. If the losses in the line are low, you can measure the SWR at the end of the feeder - at the transmitter, and the feeder can be of any length. If line losses increase and SWR increases, losses will increase in both cases. The error is expressed in an improvement in the SWR. If a change in the feeder length affects the change in the SWR value, then one or more of the following factors are at work:

1. Feeder is not 50 Ohm;

2. The measuring station is not designed to operate in 50-ohm circuits;

3. Significant losses in the line (feeder);

4. The feeder is part of the antenna and radiates (reactive load).

Air insulated feeders have very low losses and the losses in them will not be significant even with a high SWR value.

High-loss cables, such as thin polyethylene-insulated RG-58 cables, lose their effectiveness as SWR increases. If there are large losses in the feeder or its long length, it is very important to ensure a low SWR value along the entire length of the feeder, which should be highly regular (identical) along the entire length, solid - without inserts (inserts from another cable are especially undesirable). Tuning to the minimum SWR should be done at the antenna, since no matching on the part of the transmitter affects either the losses or the efficiency of the antenna system. The MFJ-259 and 269 measure SWR of any load close to 50 ohms. SWR can be measured at any frequency from 1.6 to 170 MHz, and nothing additional is required to measure SWR.

The “ANTENNA” socket of the device is the connection point for the output of the SWR meter bridge. The load is connected here - the circuit under test - the antenna feeder. To measure SWR, you simply need to connect a 50-ohm coaxial line (antenna feeder) to this jack, disconnecting it from the transmitter, which is not used when measuring SWR, because MFJ has an internal oscillator. The switch for the type of work should be set to position A (indicated on the display), because to measure the frequency of the device's internal oscillator. To measure SWR at a specific frequency, by manipulating the “TUNE” knob and the Frequency switch, we set the required frequency, monitoring it on the display. The SWR value can be read on the dial of the SWR meter (SWR).

To find the minimum SWR, you need to rotate the tuning knob of the generator “TUNE” until the needle of the SWR meter shows the minimum SWR sign. The frequency at which the minimum SWR is obtained can be read from the frequency meter display. The bandwidth of an antenna can be measured by using the criterion by which the bandwidth will be determined. For example, according to SWR=2. By rotating the generator tuning knob to the right and left from the position of the resonant frequency of the antenna (frequency with minimum SWR), on the display we see the frequency values ​​AT WHICH THE ARROW OF THE SWR METER RAISE TO SWR VALUE = 2. The lower frequency is the lower limit of the antenna bandwidth, the higher frequency is the upper frequency (limit) of the antenna bandwidth.

Resistance measurement.

The RF bridge assembly provides accurate measurement of the resistance of only the active load, which is ensured at SWR=1 (and a resistance of 50 Ohms), i.e. at the resonant frequency of, for example, an antenna. If its resonance is 3.5 MHz, then at a frequency of 3.7 MHz the indicator readings will be incorrect, since it will not be purely active resistance that is measured, but active plus reactive. If the device readings are 50 Ohms and the SWR is high, then the load is also complex, i.e. active plus reactance. At SWR = 1 for a given RF bridge, the device should show 50 Ohms of purely active (not reactive) resistance. If reactance is present or the active load is not equal to 50 Ohms, the SWR cannot be equal to 1. If the SWR meter shows SWR = 1, and the resistance meter shows a different (not 50 Ohms) value, then a so-called instrumental error occurs, associated with, for example, with radio frequency interference to the device.

Frequency measurement.

The MFJ-259 and MFJ-269 frequency meter can measure the frequency of electrical vibrations in the range from a few hertz to 200 MHz. For frequencies above 1 MHz, the sensitivity of the device is 600 mV. Below 1 MHz it is required to apply a TTL level square wave with a peak-to-peak 5V peak to peak. We turn on the power of the MFJ device, use the frequency meter input switch (type of work switch) on the top panel of the device body to set the external frequency measurement mode, as evidenced by the letter “B” appearing on the display. The button turns on three positions in sequence - measurement of the frequency of the internal generator, external measurement without turning off the internal generator and external measurement with turning off the internal generator. We connect the signal circuit whose frequency needs to be measured to the BNC socket (input of the frequency meter).

It should be noted that circuits containing constant voltages and high powers cannot be connected to any input of the MFJ-259. The frequency of the transmitter can be measured, for example, by connecting a piece of wire to the input of the frequency meter, forming a communication loop with the RF source, a telescopic antenna, the length of which should be changed depending on the distance and power of the transmitter until stable readings are obtained. If there is no RF source nearby, then you can check the operation of the frequency meter (from an external socket) by connecting the middle contacts of the antenna input jacks and the frequency meter input sockets with a wire jumper, manipulating the type of work switch. In two of the three positions (with the generator turned on and internal and external measurements) the frequency meter readings should not change.

By bringing the device closer or further away from the source of a powerful signal, the optimal level for a stable frequency indication is determined, starting from the lower limit, when the frequency meter still does not show anything. Otherwise, the signal from a powerful transmitter can overload the frequency meter and its “internals”, made on MOS structures, will fail.

The input of the frequency meter can be connected to the output of the transmitter through a loop or several turns of a communication coil wound over the power cable (feeder) of the antenna, and the number of turns of such a coil connected to the input of the frequency meter should be selected experimentally. The number of turns is higher if the transmitter power is low or a solid or double braided cable is used, or the operating frequency of the transmitter is low, otherwise the opposite should be done. A loop of wire placed inside a wattmeter, the equivalent of an antenna, a low-pass filter, can also serve as a sensor for a frequency meter. By successively pressing the “Gate” button, you can get on the display the frequency measurement accuracy from 4 to 7 decimal places when measuring frequency in MHz.

Setting up simple antennas

Most antennas are usually tuned by changing their geometric dimensions (the length of the elements).

Dipole

It is known that a dipole is a symmetrical antenna, therefore, for balancing when connecting a coaxial cable, it is useful to use a balun transformer. It can be made in several ways, for example, by winding several turns with a diameter of 10...20 cm with the same cable at the connection point to the antenna, or by making a separate transformer with a wire or the same cable wound on a ferrite ring.

The height of the dipole, as well as its surroundings, affects its input impedance, as well as the SWR in the supply line (feeder). Most tuned dipoles have an SWR below 1.5. Perhaps the only tuning element of a dipole is its length. The shorter the dipole, the higher the frequency it is tuned to and vice versa. This is true for the classical form of a dipole - “in line”.

There are several ways to change the tuning frequency, input impedance, and bandwidth of the dipole. For example, by increasing the thickness (diameter) of the conductors, with the same length we will reduce the tuning frequency, reduce its input impedance and increase the bandwidth. An example is the well-known antenna - the Nadenenko dipole. The same can be achieved by lowering the arms of the dipole down - you get the popular “Inverted Vee” antenna. This is all due to the additional capacitance introduced into the open oscillatory circuit.

Whip antennas

As a rule, these are asymmetrical antennas. Whip antenna manufacturers often emphasize the need for a good "ground" counterpoise system. In this case, an SWR is guaranteed at the resonant frequency, not exceeding 2. The pins are adjusted to the operating frequency, like the dipoles, by changing the length of the emitter and counterweights, if any. The pin with a counterweight system is called the “Ground plane”. The angle between the radiator and the counterweights, as in the case of the “Inverted Vee”, affects the antenna parameters. For example, a “sleeve” type antenna - where the counterweights are extended with the emitter “in line”. In fact, this is the same dipole, only vertical, the arm of which is structurally made in the form of a metal stocking or tube, put on the supply feeder at the connection point. The input impedance of such an antenna is close to 75 Ohms, but as soon as the angle between the emitter and the counterweights is reduced, the input impedance drops and at an angle of approximately 120 degrees it will be 50 Ohms, and at an angle of 90 degrees - approximately 30 Ohms.

Configuring simple antennas (dipoles and rods)

Antennas powered via 50 Ohm coaxial cable without various extension coils, circuits, capacitive loads, etc.

1. Connect the antenna feeder to the “Antenna” socket;

2. Adjust the generator to the minimum readings of the SWR meter;

3. Read and write down the frequency on the frequency meter display;

4. Divide the resulting frequency by the desired one;

5. Multiply the existing antenna length by the result obtained in step 4 - this will be the new desired antenna length.

Feed point resistance measurement (approx.)

Connect the device directly to the load (antenna) terminals. If the load is asymmetrical, check that it is connected correctly - the braid must be connected to the device body (at the coaxial connector). If the load is symmetrical, the internal power supply of the device should be used so as not to introduce asymmetry.

1. Set the range switch to the desired position;

2. Use the tuning knob to find the position with the minimum SWR;

3. Take readings from the resistance meter scale;

4. Repeat the measurement and compare the results now with a 50 ohm cable. The SWR should be equal to the ratio of the measured resistance without cable to 50 Ohms.

Finding the short circuit. (short circuit) in coaxial cables

1. Connect the end of the cable to the “Antenna” socket;

2. Turn on the device and smoothly tune the generator over the entire frequency range, starting from 1.6 MHz, observing the readings of the resistance meter. Record the frequency of the zero reading - F1.

3. Continue changing the frequency and find the second “dip” in the resistance meter readings - F2;

4. Calculate the location of K.Z. To do this, the number 492 should be divided by the frequency of the first “dip” F1 (MHz) and multiplied by the shortening factor of the measured cable (Ku). The result is location K.3. (Lкз) in feet. Since 1 Foot is 0.3048 m, the conversion factor is 3.2808398, which Lkz should be divided by to get the location in meters. Formula for calculating K.Z. (in meters) will take the final form Lkz = 149.9616 Ku / F1 (MHz)

To check the calculation, repeat the above from the other end of the cable. The truth lies in the middle between the found points of K.Z.

Checking and adjusting cable sections and transmission lines

The exact length of Lamda/2 and Lamda/4 cable sections or transmission lines can be found using an additional 5O Ohm non-inductive resistor. Accurate measurements are valid for any type of coaxial cable or 2-wire line with a characteristic impedance other than 50 ohms.

The central conductor of a piece of coaxial cable is connected in series with a 50 Ohm resistor (Fig. 1a, and the braid is connected to the body of the device.

For a 2-wire line, a 50-ohm resistor is connected in series with the shield shell of the additional PL-259 plug and one of the line conductors, the other line conductor is connected indirectly to the central conductor of the connector (connected to the “Antenna” socket of the device), Fig. 1b.

A coaxial cable can be rolled into a coil or laid in any way you like, while the open line must be pulled straight out and located at a distance of at least a meter from the surface and surrounding objects, otherwise the measurement accuracy is reduced.

To measure “odd” segments, multiples of 1/4, 3/4, 5/4 wavelength, etc., the line must be open at the far end, and closed to measure “even” segments, multiples of 1/2, 1, 3/2 wavelength, etc.

Connect the PL-259 connector (additional plug) with the SO-239 socket of the device using the measured line:

1. Determine the approximate length of the line or cable, taking into account the frequency for which the calculation is being made;

2. Measure and cut a piece of slightly longer length;

3. Measure the frequency at minimum SWR. It should be slightly lower than the desired one;

4. Divide the measured frequency by the required frequency;

5. Multiply the result by the actual length of the segment to obtain the required line length;

6. Shorten the line to the calculated length and check with the instrument readings. The minimum SWR must be close to the required frequency for which the segment is designed.

Measuring the transmission line shortening factor

1. Disconnect both ends of the transmission line and measure its physical length;

2.Connect the line as shown in RKS. 1a, for measurements that are multiples of 1/4 of the wavelength;

3. Find the lowest frequency from the entire frequency range of the device, which will have the lowest SWR. The dip will be observed slightly below 1/4 wavelength.

Mark the frequency on the display that corresponds to 1/4 of the resonance wavelength of your transmission line (feeder). Check that the low SWR will match all lengths that are multiples of 1/4, 3/4, etc.

The physical length of the line is L= 7 feet, the minimum SWR occurs at the frequency F=7.3 MHz.

Divide 246 by the frequency in MHz to get the line length as a multiple of 1/4 in free space (feet)

246/7.3 (MHz) = 33.69863 (Ft)

Divide the physical length of the line by the result obtained - you get the shortening factor

27/33.69863 - 0.8012195 or 80.12195%.

To determine in meters, we divide

246/3.2808398 (conversion factor, see above) = 74.980802.

The formulas for calculating the shortening coefficient will take the following form

1/4 St. Ave. = 74.980802/F (MHz) in meters.

Ku = L/ 1/4 St. Ave.

Rounded numbers with more decimal places may be used. Conversions from Feet to Meters are taken from the MFJ Enterprise Instruction Manual*

Measuring transmission line resistance (impedance) from 15 to 150 ohms

To do this, you will additionally need an Ohmmeter and a 250 Ohm non-inductive potentiometer. High impedance lines will require a high impedance potentiometer and an RF broadband transformer to convert the high line impedance to a low impedance close to 50 ohms.

1. Measure the frequency of 1/4 feeder as described above when determining the length of the cable sections;

2. Connect a 250 Ohm non-inductive potentiometer to the far end of the cable (connected with a rheostat);

3. Connect the feeder to the device and tune it to 1/4 frequency;

4. Observe the SWR as the frequency changes in the selected frequency sub-band or in the required frequency range;

5. Set the resistance of the potentiometer turned on - the rheostat, to the position when the KCV over the range almost does not change. The size of the SWR does not matter, only its change is important.

6. The resistance of the potentiometer is almost the same as the line resistance and can be determined with an Ohmmeter.

Losses in feeders and transmission lines

Losses from 3 to 10 dB can be measured quite simply - they must be determined at a known frequency and correlated with losses at a lower frequency.

1. Connect the feeder to the device;

2. The long end of the feeder must be either open or short-circuited;

3. Tune the device to the required frequency and monitor the SWR;

4. If the SWR is within the red sector of the SWR meter scale, then the loss is less than 3 dB. Increase the frequency to a reading of SWR = 3. This will determine the frequency limit up to which losses do not exceed 3 dB. If the SWR at the operating frequency is within the black sector, take the nearest SWR value on the scale and subtract the losses from the table in the description of the device.

You can also judge the dB loss by remembering that it decreases to 70% at half the frequency and increases to 140% at double the measured frequency. This is true when losses are distributed evenly along the entire length of the feeder, and not for one defective part of it.

Let's take, for example, an operating frequency of 28 MHz, at which we want to determine losses. At this frequency, the SWR meter needle is in the red uncalibrated sector, which means the loss does not exceed 3 dB. Increase the frequency until the arrow points to the non-calibrated point. At a frequency of 60 MHz, the arrow will indicate, for example, a value of 3. According to the table, the loss is 3 dB. Since 28 MHz is about half of 60 MHz, multiplying 3 dB by 0.7 (70%) gives 2 dB at 29 MHz.

Setting up tuners

Connect the input of the “Antenna” device to the 50-ohm input of the tuner, and connect the required antenna to the output of the tuner. It is advisable to make this connection using a manual RF switch for quickly connecting the tuner (antenna) to the device or transmitter (transceiver). Remember that the middle pin of the RF switch only connects to the tuner. Under no circumstances should you allow a direct connection between the device and the transmitter - the device WILL LOSE OPERATION.

1. Connect the device to the tuner input;

2. Turn on the device and tune to the required frequency;

3. Adjust the tuner until the SWR is equal to 1;

4. Turn off the device and connect the transmitter.

Checking Baluns - balun transformers

The asymmetrical winding of the transformer is connected to the device, and two resistors are connected in series to the symmetrical winding, Fig. 2.

The sum of resistances (strictly identical) must be equal to that for which the transformer is designed.

For example, 100 Ohm resistors - when welding a transformer with a resistance ratio of 1:4, i.e. 50:200 Ohm. The SWR is checked when the jumper touches points A, B, C. Good, i.e. a correctly calculated and manufactured transformer gives a low SWR when a jumper is connected to any of the points. In this case we are talking about a current transformer.

In the case of a voltage transformer, there will be a small SWR in a wide frequency range when the jumper is in position B and a large SWR when the jumper is in positions A and C. A voltage transformer can also be tested for low SWR by connecting resistors connected in parallel to the case, Fig. 3.

Measuring inductance L and capacitance C

To measure capacitance and inductance, you need to have calibrated inductors or capacitors, respectively. They must be selected into a set and carefully verified. The accuracy of future calculations will depend on their accuracy. The following set is recommended - inductors 330; 56; 0.47 µH, 10 capacitors; 150; 1000; 3300 pF.

Measurements can be more accurate if a range of inductances in the range of 0.5...500 μH and capacitances in the range of 10...5000 pF are used. Take an unknown capacitance (capacitor) or inductance (coil). Connect in series with a calibrated inductance or capacitance, and you get a series oscillating LC circuit, which in turn is connected to the device through a 50 Ohm non-inductive resistor.

Capacitance measurement

1. Connect Cx in series with the calibrated coil L with the largest inductance (from the set).

2. Connect the LC circuit in series with a 50 ohm resistor.

3. Rotate the tuning knob, moving through the range, find the frequency with the minimum SWR. If you don’t find one, change the frequency subrange or replace the coil with another one with lower inductance. Continue until you get low, close to 1 SWR.

4. Calculate the unknown required capacity using the formula

Cx [pf] = 1 / 0.00003949 F2 L,

where F is the frequency of the minimum SWR in MHz,

L is the inductance of the calibration coil.

Measuring inductance can be done in a similar way.

Forumla for inductance

Lx [µH] = 1 / 0.00003948 F2 L,

where Г is the frequency with minimum SWR in MHz,

C - calibration capacitance in pF.

Resonant Frequency Measurement

There are two ways to measure resonant frequency.

First way.

A 50-ohm resistor with short leads is connected in series with the circuit and connected to the device as shown in Fig. 4.

This method is valid for circuits with high capacitance and low inductance. In the case of large inductance and small capacitance, a series connection of capacitance and inductance should be used as shown in Fig. 5. The resonant frequency of the circuit in both cases is determined by the readings on the display of the frequency meter when tuning the frequency to the minimum SWR. It is possible to connect an additional diode detector and a high-resistance voltmeter (Fig. 6). Resonance is noted according to the maximum readings (maximum DC voltage) of an external high-resistance voltmeter.

Second way.

It involves connecting a small coupling coil (3 turns) to the device and inductively coupling this coil with the coil of the circuit whose frequency needs to be determined. The frequency is adjusted across the range until a decline in the readings of the SWR meter is obtained. The roll-off indicates the absorption of energy by the tuned circuit at the resonant frequency, the value of which can be read on the display of the frequency meter.

Part 3.

Antenna matching and matching devices

In amateur practice, it is extremely rare to use antennas whose input impedance is equal to the wave impedance of the feeder, and in turn, the output impedance of the transmitter (ideal matching option).

Most often, there is no such correspondence and special matching devices have to be used. The antenna, feeder and transmitter output should be considered as a single system in which energy must be transmitted without loss.

The implementation of this difficult task will require coordination in two places: at the point of connection of the antenna with the feeder and the feeder with the transmitter output. The most popular are various types of transforming devices: from resonant oscillatory circuits to coaxial transformers in the form of sections of coaxial cable of the required length. All of them are needed to match resistances, which ultimately leads to minimizing losses in the transmission line. And, most importantly, to reduce out-of-band emissions.

As a rule, the standard output impedance of almost all modern broadband transmitters (transceivers) is 50 ohms. Most coaxial cables used as feeders also have a standard characteristic impedance of 50 or 75 ohms. Antennas, depending on the type and design, can have an input impedance in a very wide range of values: from several Ohms to hundreds of Ohms and more.

It is known that the input impedance of single-element antennas at the resonant frequency is practically active. And the more the transmitter frequency differs from the resonant* frequency of the antenna in one direction or another, the more a reactive component of a capacitive or inductive nature appears in the input impedance of the antenna. In multi-element antennas, the input impedance at the resonant frequency is complex, since passive elements contribute to the formation of the reactive component.

In the case when the input impedance of the antenna is purely active, it is not difficult to match it with the feeder impedance using any of the suitable transforming devices. At the same time, the losses are quite insignificant. But, as soon as a reactive component is formed in the input resistance, the matching becomes more complicated, and a more complex matching device is required that can compensate for the unwanted reactivity. And this device must be located at the antenna feed point. Uncompensated reactance worsens the SWR in the feeder and increases losses.

An attempt to fully compensate for reactivity at the lower end of the feeder (at the transmitter) is unsuccessful, since it is limited by the parameters of the feeder itself. Tuning the transmitter frequency within narrow sections of the amateur bands does not lead to the appearance of a significant reactive component, so in most cases there is no need to compensate for reactance. Properly designed multi-element antennas also do not have a large input reactance component, and compensation is usually not required.

On the air, disputes often arise about the role and purpose of the antenna matching device (antenna tuner) when matching the transmitter with the antenna. Some have high hopes for it, others consider it an unnecessary toy. What actually (in practice) can and cannot help an antenna tuner?

First of all, a tuner is a high-frequency impedance transformer that can, if necessary, compensate for reactance of a capacitive or inductive nature.

Let's look at a simple example:

A split vibrator (dipole), which has an active input impedance of about 70 ohms at the resonant frequency, is connected by a 75-ohm coaxial cable (feeder) to a transmitter whose output impedance is 50 ohms. The tuner is installed at the output of the transmitter and in this case acts as a matching unit between the feeder and the transmitter, which it easily copes with.

If the transmitter is tuned to a frequency different from the resonant frequency of the antenna, then reactivity will arise in the input impedance of the antenna, which will immediately appear at the lower end of the feeder. The tuner is also able to compensate for it, and the transmitter will again be matched to the antenna feeder.

What will happen at the output of the feeder, at the point of its connection to the antenna?

Using a tuner only at the transmitter output, full compensation will not be possible, and losses will occur in the feeder due to inaccurate matching with the antenna. In this case, you will need another tuner, which will have to be connected between the feeder and the antenna, then it will correct the situation and compensate for the reactivity. In this example, the feeder acts as a matched transmission line of arbitrary length.

One more example:

A loop antenna having an input impedance of approximately 110 ohms must be matched to a 50 ohm transmission line. Transmitter output 50 ohm. Here you will need a matching device installed at the point where the feeder connects to the antenna. Typically, many hobbyists use various types of RF transformers with ferrite cores, but it is more convenient to make a quarter-wave coaxial transformer from a 75-ohm cable.

Cable length A/4 x 0.66, where

I am the wavelength

0.66 is the shortening factor for most known coaxial cables.

A coaxial transformer is connected between the antenna input and the 50 ohm feeder.

If it is rolled into a coil with a diameter of 15...20 cm, then it will also serve as a balancing device. The feeder and transmitter are automatically matched when their resistances are equal. In this case, you can refuse the services of an antenna tuner altogether.

For this example, another coordination method is possible:

Using a half-wave or a multiple of half-wave coaxial cable with any characteristic impedance (also taking into account the shortening factor). It is connected between the antenna and the tuner located near the transmitter. The antenna input impedance of about 110 ohms is transferred to the lower end of the cable and, using the tuner, is transformed into an impedance of 50 ohms. In this case, there is complete coordination of the antenna with the transmitter, and the feeder acts as a repeater.

In more complex cases, when the input impedance of the antenna does not match the characteristic impedance of the feeder, and the impedance of the feeder does not match the output impedance of the transmitter, two matching devices are needed. One at the top for matching the antenna with the feeder, the other at the bottom for matching the feeder with the transmitter. And it is not possible to get by with only one antenna feeder to coordinate the entire chain: antenna - feeder - transmitter.

The presence of reactivity further complicates the situation. The antenna tuner in this case will significantly improve the matching of the transmitter with the feeder, thereby facilitating the operation of the final stage, but nothing more. Due to mismatch between the feeder and the antenna, losses will occur, and the efficiency of the antenna itself will be reduced. The switched on SWR meter between the transmitter and the tuner will record SWR=1, but this will not happen between the tuner and the feeder due to the mismatch between the feeder and the antenna.

A completely fair conclusion arises: the tuner is useful in that it supports the normal mode of the transmitter when operating on an unmatched load, but at the same time it is not able to improve the efficiency of the antenna when it is mismatched with the feeder.

The P-circuit used in the output stage of the transmitter can also act as an antenna tuner, but subject to prompt changes in inductance and both capacitances.

As a rule, antenna tuners, both manual and automatic, are resonant loop tunable devices. Manual ones have two or three regulating elements and are not efficient in operation. Automatic ones are expensive, and for working at high power they are very expensive.

Let's look at a fairly simple broadband matching device (tuner) in Fig. 1, which satisfies most variations in matching the transmitter to the antenna:

Rice. 1. HF transformer circuit

It is very effective when working with antennas (loops, dipoles) used on harmonics when the feeder is a half-wave repeater. In this case, the input impedance of the antenna is different on different bands, but with the help of a matching device it is easily matched to the transmitter. The proposed tuner can operate at transmitter powers of up to 1.5 kW in the frequency band from 1.5 to 30 MHz.

The main elements of the tuner are an RF autotransformer on a ferrite ring from the deflection system of the UNT-35 TV and a 17-position switch. It is possible to use conical rings from TVs UNT-47/59 or others.

The winding contains 12 turns wound into two wires. The beginning of one winding is connected to the end of the other. In the table and diagram the numbering of turns is continuous. The wire itself is multi-core in fluoroplastic insulation. Wire diameter 2.5 mm insulation. Taps are made from each turn, starting from the eighth from the grounded end.

The switch is ceramic, biscuit type with 17 positions.

The autotransformer is located as close as possible to the switch, and the connecting conductors between them must be of a minimum length. It is possible to use a switch with 11 positions while maintaining the design of the transformer with fewer taps, for example, from 10 to 20 turns. But in this case, the resistance transformation interval will also decrease.

Knowing the input impedance of the antenna, you can use such a transformer to match the antenna with a 50 or 75 ohm feeder, making only the necessary taps. In this case, it is placed in a moisture-proof box, filled with paraffin and installed at the antenna feed point.

Also, this matching device can be made as an independent structure or be part of the antenna-switching unit of the radio station.

For clarity, the mark on the switch handle (on the front panel) indicates the resistance value corresponding to this position. To compensate for the reactive component of an inductive nature, it is possible to connect a variable capacitor C1, Fig. 2.

Rice. 2. Complete circuit of the matching device

The dependence of the resistance on the number of turns is given in Table 1. The calculation was made based on the resistance ratio, which is a quadratic function of the number of turns.

Table 1.

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