UW3DI Bible. Thermal compensation can be considered complete
A. Pershin UA9CKV
The transceiver is designed for amateur radio communications in the short wave range of 1.8...29 MHz. Type of work: telephone (SSB) and telegraph (CW). The transceiver is entirely made on semiconductor devices and microcircuits, has a built-in digital scale (according to the diagram of radio amateur V. Krinitsky (RA9CJL), published in this collection), and a built-in power supply. The transceiver provides for the connection of an external GPA, which allows radio communications at different frequencies.
When developing the transceiver, the main attention was paid to obtaining high dynamic parameters of the receiving path and good ergonometric characteristics of the transceiver as a whole.
The absence of an RF amplifier at the receiver input, the use of a high-level balanced mixer, a low-noise and linear IF path made it possible to achieve the first task. The second problem was solved by using non-tunable bandpass filters at the receiver input, electronic switching of ranges and the “transmit-receive” mode.
Rice. 1. Functional diagram of the Ural-84 transceiver
The transceiver (Fig. 1) is made according to a circuit with one frequency conversion. The choice of an intermediate frequency of 9100 kHz is determined by the presence of a homemade quartz filter, made according to the method described in the magazine "Radio" No. 1, 2 for 1982 (it is possible to use an industrial quartz filter of the FP2P-410-8.815 type with minor changes in the circuit diagram). The common components of the transceiver in the transmit-receive mode are: low-pass filters Z1, band-pass filters Z2, mixer U1, reversible matching stage A1, smooth range generator G1, quartz filter Z3.
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Basic technical data of the transceiver |
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Sensitivity of the receiving path at a signal-to-noise ratio of 10 dB, µV, no worse |
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Dynamic range by "clogging", dB |
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Two-signal selectivity (with signal detuning 20 kHz), dB |
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Switchable bandwidth: in SSB mode, kHz |
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in CW mode, kHz |
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AGC control range (when the output voltage changes by no more than 6 dB), dB, no less |
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Frequency drift of the smooth range generator at the highest frequency in 20 minutes after a half-hour “warm-up”, Hz, no more |
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Output power of the transmitting path, measured at the antenna equivalent (R=75 Ohm), W, not less |
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Suppression of carrier and non-operating sideband frequencies, dB, no less |
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Antenna input impedance, Ohm |
The nodes are connected for reception or transmission using relay contacts K1, K2, as well as switch S1. The diagram shows the nodes in receive mode. The signal from the antenna input through low-pass filters Z1, a step attenuator ATT and three-circuit bandpass filters Z2 is fed to the balanced mixer U1. The same mixer is supplied with voltage from the smooth local oscillator G1. The converted signal passes through a matching stage of the reversible type L/and then to the quartz filter Z3, is amplified by node A2 and goes to the mixer U2, where it is mixed with the voltage from the reference quartz oscillator G2. The low-frequency signal from the output of the mixer goes to the low-frequency amplifier A3 and from it to the loudspeaker BA1.
When switching from reception to transmission, a corresponding switching of functional units occurs. This is done either manually or by a voice control system. The signal from the BFJ microphone, amplified by node A4, is sent to the voice control device A8, which in turn controls the switch S1, as well as to the mixer U3, which contains voltage from the reference oscillator. The generated DSB signal is amplified by node A5, passes through a quartz filter Z3, where an intermediate frequency voltage of 9100 kHz with an upper sideband is isolated and fed through node A1 to mixer U1, the other input of which is supplied with a smooth local oscillator voltage. The operating frequency signal isolated by bandpass filters Z2 from the output of mixer U2 is sent to amplifier A6 and then, amplified in power in node A7, through low-pass filter Z1 it is sent to antenna WA1.
The telegraph signal is generated in the transceiver using a manipulated generator G3, which is connected to node A5, instead of a single-sideband signal generating device.
The transceiver is made according to the block principle. In the diagram, the numbering of elements in each block is different.
On the main board (node A6, Fig. 2) there is a reversible mixer, a matching stage, a receiver IF path, quartz filters, a mixing detector, a low-frequency amplifier of the receiver, an AGC circuit, and a broadband voltage amplifier of a smooth local oscillator.
Fig.2a. Schematic diagram of the main transceiver board (node A6)
Fig.2b. Schematic diagram of the main transceiver board (node A6)
High-level passive mixer VD1 - VD8, T2, T3 is assembled using a double balanced circuit. Its peculiarity is the use of broadband transformers with a volumetric short-circuited turn (the design is described in the magazine "Radio" No. 1, 1983). If modern high-frequency diodes like KD514A (or even better, Schottky barrier diodes like AA112) are used in the mixer, the signal loss in it will be about 4...5 dB. When received, the signal goes to the primary winding L3 of transformer T2. The converted signal is taken from the midpoint of winding L4. The smooth local oscillator voltage is amplified by a wideband amplifier using a VTI transistor and supplied to the input winding L7 of transformer T3. A powerful field-effect transistor VT2 is used to assemble a cascade for matching the mixer with a quartz filter. The KP905 type transistor was chosen due to its good noise parameters and linearity. When receiving, the cascade operates as an amplifier with a common gate and a gain of about 12 dB; its input impedance is active and constant over a wide frequency range. Matching with an eight-crystal SSB crystal filter at a frequency of 9100 kHz is provided using autotransformer L12.
The circuits of quartz filters ZQ1 and ZQ2 are shown in Fig. 3 and 4.
Rice. 3. Schematic diagram of the ZQ1 quartz filter
Rice. 4. Schematic diagram of the ZQ2 quartz filter
Filter ZQ1 has the following parameters:
If the ZQ1 filter uses quartz resonators from the Granit radio station with frequencies of 9000...9150 kHz, then the capacitance values in the filter circuit may remain unchanged.
In the ZQ2 filter, the bandwidth can be changed. In SSB mode it is 2.3 kHz, and in CW mode, when 68 pF capacitors are connected in parallel with the quartz resonators, the bandwidth is narrowed to 800 Hz.
During transmission, the cascade on transistor VT2 is a source follower. Reversing the operating mode of this cascade is carried out by switching voltages from the control buses. When receiving +15 V in the Rx bus, 0 V in the Tx bus. When transmitting 0 V in the Rx bus, +15 V in the Tx bus. Diode switches VD9 and VD10 connect the “hot” end of the autotransformer L12 to the drain of the transistor when receiving or to its gate when switching to transmission. Grounding of the “cold” end of the autotransformer L12 at high frequency during reception occurs through the diode switch VD10 and capacitor C5, and during transmission through the diode switch VD9 and capacitor C4.
The first stage of the amplifier, which has a gain of about 20 dB, is assembled on transistors VT5, VT6. The L17C29C30 P-circuit allows you to match the transistors of the cascode circuit and carry out additional filtering of the useful signal. The cascade load is the L16C26 circuit. Coordination with the second quartz filter ZQ2 is carried out using the coupling coil Lсв. This filter is assembled using a 4-quartz ladder circuit and has a 3 dB passband of 2.6 kHz. In the mode of receiving telegraph signals, it is switched using a relay of the RES-49 type to a narrow band of about 0.7 kHz by connecting a filter of capacitances equal to approximately 68 pF in parallel with the quartz filter. The use of two quartz filters ZQ1 with a passband of 2.4 kHz and ZQ2 significantly improved the rejection of signals outside the transparency band of the filters, which reached 100 dB. The main signal amplification is carried out in cascade on the DA1 K224UR4 microcircuit (K2US248 - old designation). The mixing detector on transistors VT8, VT9 has no special features. Between the detector and the input of the low-frequency pre-amplifier on the DA2 chip, a ZQ3 low-pass filter of type D3.4 (from Granit radio stations) is connected, which improves the noise and selective parameters of the receiving path. The ULF output stage is assembled according to the usual circuit using transistors VT15, VT16, VT17. An electronic switch is assembled on transistor VT14, with the help of which the ULF input is bypassed in transmission mode. In telegraph mode, this key is closed, which allows you to listen to the self-monitoring signal during transmission.
The AGC circuit consists of an AGC pre-amplifier DA3, VT13, an emitter follower VT12, AGC detectors VD18, VD19 and VD24. An auxiliary “fast discharge” circuit with a discharge time of about 0.2 s is assembled on transistor VT11 and diode VD17.
When a useful signal is received, the AGC discharge time is determined by the main circuit R36C53. When the signal disappears, a rapid discharge of C53 occurs through the diode VD17 and transistor VT11. From the source follower VT10, the positive AGC voltage, which increases with increasing signal strength, is supplied to the control transistors VT4 and VT7, which control the amplification of the IF stages. To implement the AGC delay, the source of transistor VT6 is connected to a reference voltage source collected on the zener diode VD11 and resistor R25. In transmission mode, transistors VT4, VT7 are supplied with a switching voltage of +15 VTX-O BRX, which practically closes the IF path of the receiver. An adjustable amplifier operating in SSB or CW signal transmission mode is assembled on the VT3 transistor. The cascade gain is adjusted by changing the voltage on the second gate VT3 and reaches a depth of more than -40 dB. If desired, the ALC voltage can be applied to the second gate of this transistor.
In node A2 (Fig. 5) there are: a step attenuator of the receiver, a switching relay K17, bandpass filters, and preliminary stages of the transmitter. In the receiving mode, the signal from node A1 is sent to an attenuator made of two resistor P-links: R1R2R3, providing an attenuation of 10 dB and R4R5R6 - 20 dB. The attenuator is controlled by a switch on the front panel of the S7 "ATT" receiver, which has the positions "O", "10 dB", "20 dB", "30 dB". P-links are switched by relay contacts K13 - K.16 type RES-49 (RES-79). After the attenuator, the signal passes through the normally closed contacts of relay K17 (RES-55A) and enters three-circuit bandpass filters, the selection of which is made by six “Range” push-button switches (SI - S6) with dependent fixation. Switching of band filters is carried out using relays K1 - K12 type RES-49 (RES-79). Bandpass filters suppress the image channel by more than 80 dB.
Fig.5. Schematic diagram of a pre-power amplifier and bandpass filters (node A2)
The use of relays for switching bandpass filters and an attenuator is due to the desire to achieve the highest possible dynamic range, while switching using diode switches (p-i-n diodes, etc.) is unjustified due to a significant decrease in the dynamic range and an increase in the noise of the receiving path.
After bandpass filters, the signal enters node A6, discussed earlier. In transmission mode, the SSB or CW signal voltage coming from node A6 passes through bandpass filters in the opposite direction and through the contacts of relay K17 is supplied to a broadband amplifier made on microwave transistors VT2, VT3, VT4, where it is amplified to level 5...7 In eff. with unevenness in the range from 1.8...35 MHz no more than 2 dB.
The pre-amplifier load is a broadband transformer 77 with a volumetric short-circuited turn, similar to the mixer transformers in node A6. The T2 broadband transformer is made of 16 ferrite rings placed on a copper tube (the design is described in Radio magazine No. 12, 1984). Chains R10R11C6 and R23C14 carry out frequency correction of the frequency response of the preamplifier. Resistors R13, R24 are selected according to the minimum unevenness of the output voltage over the entire range of amplified frequencies. The cascade on transistor VT1 is an electronic switch with a delay necessary for switching the antenna circuit in node A1.
Node A1 - transmitter power amplifier (Fig. 6) is made on a powerful field-effect transistor VTI type KP904A. There are also low-pass range filters (P-circuit) and switched relays of the RES-10 type.
The signal voltage at the operating frequency from the preamplifier is applied to the gate of the VTI transistor and amplified to an output power of about 30 W. The cascade load is a broadband transformer made on a ferrite ring with a permeability of 300NN and a diameter of 32 mm according to a well-known method. The maximum drain current of the transistor reaches 2 A. Through the contacts of relay K13, closed during transmission, the amplified signal passes through a low-pass filter and enters the antenna (connector XI). Resistor R5 is used to set the initial current of the transistor. Frequency-dependent OOS is implemented through the R7C31 chain. The power amplifier has fairly good linearity. With the correct selection of the quiescent current, out-of-band emissions are suppressed to -50 dB.
In the receiving mode from socket XI, the signal passes through range low-pass filters and through the normally closed contacts of relay K13 (type RES-55A) goes to range bandpass filters (node A2).
As practice has shown (more than 6,000 connections were made on the transceiver), fears that the relatively low-power relays in the power amplifier will often fail are unfounded, since all their contacts switch in the absence of a signal.
Smooth range generator - node A3 (Fig. 7) consists of six separate range generators, switched by power supply in the second direction (the first is for switching bandpass filters) of push-button switches S1 - S6. The generator is directly assembled on the VTI field-effect transistor using an inductive three-point circuit. Transistor VT2 is an emitter follower. The load of all six emitter followers is resistor R6. The voltage drop across it, equal to about +5 V, closes the emitter junctions of non-working repeaters, thereby eliminating the influence on the frequency of the operating generator of other band generators. ..The distribution of VFO frequencies by range and circuit data are given in table. 1. VFO frequencies are selected in such a way that when the range is changed, the desired sideband is automatically selected. Using relays K1, K2 (RES-55A), an external GPA can be connected to the transceiver. The absence of mechanical switching, as well as the presence of separate circuits for each range with their careful thermal compensation, made it possible to achieve good stability without resorting to frequency multiplication. This construction of the local oscillator allows you to optimize the output voltage levels, create frequency overlap, and make the detuning value independent for each range.
Table 1
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Range |
GPA frequency, MHz |
Winding pitch, mm |
Note |
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Silver plated 0.8 |
Frame - ceramics with a diameter of 12mm Hot winding, tension with BF-2 glue and drying 100°C |
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Silver plated 0.8 |
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The SSB and CW signal voltage conditioner - node A4 is shown in Fig. 8.A reference quartz oscillator with a frequency of 9100 kHz is assembled on the VTI transistor. Transistor VT2 is a buffer stage, from which the reference oscillator signal is supplied to the balanced modulator on varicaps VD1, VD2 and transformer T1. The modulator has high linearity and allows you to suppress the carrier frequency by at least 50 dB. The cascade on the DA1 chip [is a microphone ULF, from the output of which the amplified low-frequency voltage is supplied to the midpoint of the L3 winding of the balanced modulator and through the emitter follower VT6 to the voice control system (VOX). The cascade on the VT5 transistor is a manipulated telegraph local oscillator, stabilized by quartz ZQ2 Its frequency is 800...900 Hz higher than the frequency of the reference local oscillator, i.e. it coincides with the “transparency” band of the quartz filter ZQ1.
Depending on the type of operation, telephone or telegraph, voltage is supplied to the emitter follower VT4 through the contacts of relay K1 either from a balanced modulator (SSB) or from a telegraph local oscillator (CW). From the output of transistor VT4, the signal is supplied for further conversion to node A6 (main board). Using the tuning resistor R21, the required gain of the microphone ULF is set; using resistors RI8, R15, the carrier frequency of the reference local oscillator is balanced. Inductance L1 serves to accurately set the frequency of the reference local oscillator on the lower slope of the characteristic of the ZQI quartz filter.
Operating the transceiver in "receive" mode or<передача" управляет коммутатор - узел А7 (рис. 9). Собственно коммутатор выполнен на мощных транзисторах VT5 - VT9. Транзисторы VT1. VT3, VT4 входят в систему VOX. VT7 - Anti-VOX. С помощью подстроечного резистора R1 устанавливается задержка срабатывания системы голосового управления, a RIO - порог срабатывания системы VOX. Резисторы R14 устанавливает порог срабатывания системы Anti-VOX. На транзисторах VT10 - VT12 выполнен стабилизатор напряжения плавного гетеродина +9 В. На транзисторе VT13 собран усилитель S-метра. В режиме приема на его вход через диод VD7 подается напряжение АРУ с основной платы, а через диод VD8 напряжение с узла А1, пропорциональное току стока мощного транзистора VT1. С помощью подстроечного резистора R19 устанавливается нуль S-метра, a R20 служит для калибровки.
Fig.9. Schematic diagram of the RX - TX switch, +9 V voltage stabilizer and S-meter amplifier (node A7)
The switch can be controlled from a pedal connected to pin 9 of connector XI in both SSB and CW modes. In CW mode, positive pulses applied to pin 7 of connector XI from the electronic automatic telegraph key affect the voice control system, i.e., half-duplex operation of the transceiver can be carried out. Voltages +15 V TX - O V RX are removed from pins 1.3 of connector X1 and supplied to the transceiver nodes.
The +40 V and +15 V stabilizers in the power supply (Fig. 10) are made according to well-known circuits and are current protected.
The connection diagram of the transceiver nodes is shown in Fig. 11. The frame is made of duralumin sheets 5 mm thick, connected at the end using M2.5 screws. The front and rear panels have dimensions of 315X130 mm and are fastened together by two side panels measuring 270X130 mm.
The sidewalls are installed at a distance of 40 mm from the edges of the front and rear panels, forming basements in which printed circuit boards are located: on the left - the board of node A2, on the right - nodes A7, A5 (electronic telegraph key). Between the sidewalls, at a height of 40 mm from the lower edge of the front and rear panels, a subchassis measuring 225X150 mm is fixed. Local oscillator A2 and driver A4 boards are installed on top of it. Below in the basement there is the main A6 board, and between the sidewalls at a height of 25 mm from the lower edges of the front and rear panels there is a second subchassis measuring 225X80 mm. It has a power supply transformer installed on the top right, and a +40 V and +15 V stabilizer board on the bottom, in the basement. Figures 12, 13 and 14 show the dimensions of the front, front and rear panels of the transceiver.
The power amplifier assembly is located in a shielded box measuring 115X90X50 mm, which is attached together with a powerful output stage transistor on the left above the second subchassis to the rear panel of the transceiver. On the rear panel there is a radiator with 29 fins 15 mm high for powerful output stage transistors and voltage regulators. Radiator dimensions 315X90 mm.
Fig. 12. Transceiver front panel
Fig. 13. Transceiver front panel
Fig. 14. Rear panel of the transceiver
The boards of nodes A2, A4, A5, A6, A7 are removable. They are connected to the mounting harness using connectors of the GRPPZ-(46)24ShP-V type. The smooth local oscillator board is housed in a shielded box.
The main board A6 is made of double-sided fiberglass 1.5...2 mm thick with dimensions 210X 137.5 mm. The foil layer on the part side is not removed. The leads of the parts connected to the case are soldered to the foil on both sides of the board, forming a common ground. The remaining holes on the part side are countersunk to prevent short circuits to the common wire.
The printed circuit board of node A6 is shown in Fig. 15.
Quartz filters are made in. separate shielded and well-soldered brass boxes on B1 type resonators from Granit radio stations.
In Fig. Figure 16 shows the printed circuit board of node A4 and the placement of elements on it.
Variable capacitor - six-section from the R-123 radio station. The local oscillator circuits are placed directly in the sections of the capacitor separated by partitions. It is possible to use variable capacitors from R-108 radio stations. In this case, two capacitors are taken and, using the existing gear, synchronously connected to each other, allowing the creation of an eight-band VFO.
The transceiver uses permanent resistors of the MLT-0.125 (MLT-0.25) type, and trimmers of the SP4-1 type. Relays - RES-55A (RS4.569.601), RES-10 (RS4.524.302), RES-49 (RS4.569.421-07). Variable resistors type SPZ-12a. Capacitors type KM, KLS, K50-6.
High-frequency chokes of 50 μH are wound on ferrite rings F-1000NN K7X4X2 and have 30 turns of PELSHO 0.16, and chokes of 100 μH have about 50 turns.
Bandpass filter circuit data is given in Table 2. The diameter of all coils here is 5 mm, the core is SCR type SB12A.
table 2
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number of turns |
number of turns |
number of turns |
number of turns |
Number of turns |
number of turns |
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Capacity, pf |
Capacity, pf |
Capacitance, pF |
Capacity, pf |
Capacity, pf |
Capacity, pf |
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IN table 3 winding data for the remaining elements is given.
Table 3
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Designation |
Number of turns |
Frame, magnetic circuit |
Note |
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Winding on a mandrel, frameless. The winding pitch is selected during setup |
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It is made according to the design of a transformer with a volumetric turn. The design is described in Radio 1984, No. 12 |
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8X2 ring |
Copper tube |
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M600NM K 10Х6Х3 |
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0 5 mm, heart. SCR |
L3 - in two wires, L4 - evenly on top of L3 |
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20VCh K10H6HZ |
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Same as 2T1 |
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20VCh K10H6HZ |
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М1000НМ К10Х6ХЗ |
Winding in two wires |
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Dia.5 mm H=20 mm |
Winding ordinary, screen 16Х16Х |
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Lsv=4 turns |
SCR core |
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20VCh K10H6HZ |
Trifilar winding |
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Winding with 6 strongly twisted wires, 3 wires in parallel |
The contours of the bandpass filters are placed in aluminum screens with dimensions of 20X20 mm and a height of 25 mm.
The power supply transformer with an overall power of about 70 W is wound on a tape ring magnetic core OL50/80-40. The primary winding is wound with PEV-2 0.41 wire and contains 1600 turns. The secondary winding is wound with PEV-2 1.5 wire and contains 260 turns.
Transistor KP905 in node A6 can be replaced with KP903A. Configuring the transceiver. Before installing elements on the boards, you must check their serviceability. First, each board is configured separately. For this, a separate power source and the necessary devices are used.
It is advisable to carry out the settings in the following sequence :
Node A7. The collector of transistor VT1 is connected to the common wire and resistor R7 is selected so that the residual voltage at the collector of transistor VT6 is no more than +0.3 V. The connections are restored. Selection of resistors R8. R9 sets the voltage on the VT9 collector close to zero, but not more than +0.3 V. Pins 1, 3 on connector XI should be loaded when configured with resistors with a resistance of about 30 Ohms and a dissipation power of at least 5 W.
Node A3. Setting up range generators consists of setting the generating frequency indicated in table. 2, using capacitors C2, C3 and the number of turns of inductance L1 (the tap from the coil is taken from 1/4-1/5 of the turns). Capacitor C4 is selected to be minimal, controlling the stability of generation. By selecting C5, the required frequency detuning is established. Finally, careful thermal compensation of the circuit is carried out using a capacitor SZ, composed of groups with different TKE. During thermal compensation, the GPA box heats up to 35...40 °C. The output voltage across resistor R6 should be 0.15...0.2 Veff.
The RF voltage at the drain of transistor VT3 supplied to the modulator should be about 2 Veff. The low-frequency voltage at the output of the DA1 microcircuit should be 1...1.5 A, when a voltage from a sound generator with a frequency of 1000 Hz and an amplitude of 3...5 mV is applied to the microphone input. The modulator is configured as follows: first, by connecting an RF millivoltmeter to the VT4 emitter, use C26 to tune the L3C26VD1VD2 circuit to resonance at the maximum signal. Then the input of the microphone amplifier is short-circuited and by sequential adjustment of resistors R18, R15 the modulator is balanced for maximum suppression of the carrier frequency at the minimum RF voltage at the emitter VT4.
Setting up the manipulated oscillator involves setting the frequency of the ZQ2 quartz oscillator. It should be higher than the frequency of the reference oscillator by 800...900 Hz (controlled by a frequency meter on pins 5, 28 of connector XI). The output voltage at this point should be about 0.3 V, .. both in telegraph and telephone mode (when pronouncing a loud “a ... a”). At the output of the emitter follower VT2, the voltage of the reference oscillator should be 1.5...1.8 Veff.
Node A6. The board setup begins with the ULF receiver. Its sensitivity should be 5...10 mV at normal output volume. The VT8, VT9 detector is balanced with the reference local oscillator voltage applied and the input shorted by adjusting resistor R31 to minimize noise at the output of the amplifier. Setting up the amplifier has no special features and consists in setting the circuits to the average frequency of the quartz filter (with the AGC system disabled, pin 11 of connector X1 is short-circuited to ground). At the output of the AGC system (pin 13 of connector XI), the DC voltage should reach a positive value of about +5 V when a voltage of about 30...40 mV is applied to its input (capacitor C75) from the sound generator.
The GPA voltage supplied to the balanced modulator (on winding L7) should be 1.3... 1.5 Veff. When transmitting, the SSB or CW signal voltage at the source of transistor VT2 should not exceed 0.3 Veff. The constant voltages on the collectors of transistors VT4 and VT7 are +9 V and +2.6 V, respectively. In this case, the mixer must be supplied with GPA voltage. When an input signal of about 1 mV is applied to winding L3 from an RF generator, the voltages on the collectors of these transistors are reduced to +0.4 V and +0.3 V, respectively. The AGC system is turned on. After setting up the main board, its sensitivity from the input should be 0.2...0.3 µV.
Particular attention must be paid to coordination quartz filters with IF stages. When setting up quartz filters, it should be taken into account that their parameters largely depend on the capacitances of the measuring circuit connected in parallel with the inputs and outputs of the filters. For this reason, it is recommended to adjust the filters using the measuring circuit shown in Fig. 18. In this case, capacitors C12 in the eight-crystal filter and C4 in the four-crystal filter must be temporarily unsoldered.
Rice. 18. Schematic diagram of the measuring device
and settings of ZQI and ZQ2 quartz filters
Node A2. Bandpass filters are tuned using a well-known method, but it is necessary to load their inputs and outputs with 75 Ohm resistors. The wideband amplifier using transistors VT2, VT3, VT4 is first adjusted to direct current. The constant voltage on the collector VT3 is +15...20 V, the quiescent current of the transistor should be about 70...80 mA. Then the unevenness of the output voltage is checked and selected using resistors R13, R24 when a signal of 100...150 mV in the range of 1.8...30 MHz is applied to the input of the bandpass filter from the GSS. In this case, a capacitance of about 270 pF is connected in parallel to resistor R24 (the input capacitance of the KP904A is simulated). The RF voltage at the output should be 5-7 Veff.
Node A1. The equivalent of a 75 Ohm antenna with a power of at least 30 W is connected to the output of the cascade and the output power is checked. Low-pass filters must first be tuned using the "cold" tuning method. The "quiescent" current of the KP904A transistor should be about 200 mA. Its setting is done using potentiometer R5.
After careful adjustment of individual components, a comprehensive setup of the transceiver is carried out in all operating modes - “reception”, “transmission”, “tone”.
Literature:
- The best designs of the 31st and 32nd exhibitions of radio amateur creativity. M. DOSAAF, 1989, p.58-70.
Schematic diagram of a simple smooth range generator on the HC4046 chip, Frequency up to 50 MHz.
The NS4046 chip (as well as analogues MM74HC4046N, MJM74HC4046 and others) is an RC oscillator with a PLL capable of generating a stable frequency up to 50 MHz, which allows you to make a VFO (smooth range generator) for a HF broadcast receiver or communication equipment, the advantage of which will be a stable frequency at the output and the complete absence of LC frequency-setting circuits.
The setting will be carried out by changing the voltage at pin 9 of the microcircuit using a variable resistor or an electronic circuit that synthesizes the voltage.
Schematic diagram
The figure shows a circuit of a generator that produces a frequency from 2.5 MHz to 40 MHz, variable in four subranges, which are switched by switch S1. In this case, the frequency adjustment in each sub-band is carried out roughly by resistors R1-R4 and smoothly by resistor R5.
The purpose of this entire circuit on resistors R1-R5, R7 is to regulate the constant control voltage at pin 9 of D1. In addition, the frequency also depends on the resistance R6. Table 1 summarizes the frequency data in the subbands with R6 equal to 22K and 6.8K.
Rice. 1. Smooth range generator circuit up to 50 MHz on the HC4046 chip.
By changing the voltage generation circuit at pin 9 of D1, adding resistors that limit the adjustment, and also by changing the resistance of resistor R6, you can make a GFO operating in almost any range from 2.5 to 50 MHz.
The output signal is TTL level rectangular pulses; such a signal can be supplied directly (via an isolation capacitor and, if necessary, a voltage divider) to key frequency converters. Or you can apply it to an RF transformer, at the output of which, as a result of the action of inductance, there will be pulses close to a sinusoidal shape.
Details
Table 1.
| Range | R6 = 22 K | R6 = 6.8K | |
| 1 | 2.5... 5 MHz | 7 ... 13 MHz | |
| 2 | 5... 8.6 MHz | 13... 21 MHz | |
| 3 | 8.6 ... 12.3 MHz | 21 ... 27 MHz | |
| 4 | 12.3 ... 22 MHz | 27 ... 40 MH | |
The supply voltage to the circuit must be supplied through a 5V voltage stabilizer, for example, KR142EN5A.
A stable smooth range generator can be used in transceivers whose structural diagram is similar to the UW3DI transceivers.
GPA parameters
Range, kHz 5485…6015
Frequency drift (at the middle frequency of the range), kHz, no more: during the first 15 minutes of self-warming 1
over the next 15 minutes….0.05*
for the next hour of warming up 0.02*
Harmonic coefficient, %, no more than 5
Detuning (when the control voltage changes from -12 to -24 V), kHz ±3
Output high frequency voltage. V 0.5
Load resistance, kOhm, not less than 5
The schematic diagram of the GPA is shown in Fig.
The generator itself is made using a 1V2 field-effect transistor. Loaded onto the low input resistance of the buffer stage on a 1V3 transistor connected in a common-emitter circuit. All parts of the generator, with the exception of variable and tuning capacitors 1SZ and 1S4 and resistor 1R6, are mounted in a brass screen with a diameter of 45 and a height of 60 mm.
The thickness of the screen walls is 4 mm. Capacitors 1S1, 1S10, 1S12, 1S13 - KLS, 1S2, 1S5-1S9, 1S11 - KTK-1. The color of the housings 1C2, 1C5, 1C6, 1C9 is grey, 1C7, 1C11 is blue, 1C8 is red. Capacitor 1SZ is the heterodyne section of the quad block from the R-108 radio station. A tuning capacitor 1C4 is also installed there.
Coil L1 is made on a ceramic smooth frame with a diameter of 18 mm (the frame of the heterodyne section of the R-253 receiver is used) with PEV-2 0.51 wire and contains 25 turns, wound turn to turn. The wire is secured to the frame with BF-2 glue. The tap is made from 7.5 turns in the form of a wire loop twisted and soldered before winding. After winding, the coil is dried for two hours at a temperature of 120 ° C, followed by drying for 24 hours at room temperature.
Establishing the GPA
start by checking the DC and RF voltage at the collector of transistor 1V3. A stabilized voltage of -18 V±0.1% is supplied to the varicap power circuit. When measuring DC voltage, resistor 1R6 is shunted with a capacitor with a capacity of at least 0.01 μF. By selecting capacitor 1C6 and adjusting 1C4, the range of the generator is set (with the screen cover closed).
By monitoring the temperature of the screen with a thermometer, measure the frequency stability at a constant temperature with a digital frequency meter (or, in extreme cases, with a receiver with high frequency stability, for example, P250-M2, warmed up for an hour). This operation must be performed no earlier than a quarter of an hour after soldering into the GPA. The frequency drift over 15 minutes should not exceed 100 Hz. Otherwise, it is necessary to check the quality of the parts used, and perhaps re-select the operating mode of the 1V2 transistor.
By heating the generator screen with a soldering iron to a temperature of 40...50° C and cooling it naturally (without a fan!), check the cyclic frequency change. If the steady-state frequency value after the heating-cooling cycle differs from the initial value by more than 200...300 Hz, it is necessary to find and replace a part with a non-cyclic temperature coefficient. By selecting temperature-compensating capacitors IC7 and IC8, the generator frequency from warming up is achieved by no more than 50...70 Hz/°C. Then check the thermal stability of the generator in the extreme positions of the variable capacitor.
Thermal compensation can be considered complete,
if, when the generator is tuned from one end of the range to the other, the frequency shift due to heating changes sign (for example, at the minimum frequency of the generator it decreases due to heating, and at the maximum it increases). Despite the labor-intensive nature of the described technique and its apparent complexity, it is advisable to set up the GPA in strict accordance with the stated requirements. Only in this case is guaranteed long-term and reliable operation of the device.
To increase the thermal stability of the generator, GPA thermostatting was used. The schematic diagram of the thermostat is shown in Fig.
the location of its parts installed on the screen is shown in Fig. 3. Germanium transistors 2V1, 2V2 are used as a temperature sensor, installed at the location where the L1 coil is attached to the screen.
The regulating transistor 2V9 is installed on the upper wall of the screen, and the heater Rн is made of nichrome wire from the heating element of a soldering iron with a power of 40 W for a voltage of 220 V in the form of a screen winding, previously covered with mica. The remaining parts of the thermostat are mounted on a printed circuit board measuring 100 X 40 mm.
The GPA screen is thermally insulated from the chassis of the structure using textolite bushings and washers, and its grounding is carried out with a piece of wire with a diameter of 1...2, a length of 25...30 mm, brought out from the common grounding point of the generator parts through a hole in the screen. Setting up a thermostat comes down to setting the operating temperature by selecting resistor 2R2. The recommended temperature is 40° C. The thermostat warm-up time is less than 5 minutes, the accuracy of maintaining the temperature at the location where the temperature sensor is installed is no worse than ±0.1° C, which, when setting up the GG1D according to the previously described method, corresponds to a frequency shift from heating of no more than ± 5…7 Hz.
The density of the VFO tuning scale is symmetrical relative to the average frequency (the scale is stretched in the areas of 5.5...5.6 MHz and 5.9...6 MHz). When using a disk with a diameter of 150 mm for the scale, the scale calibration accuracy can reach 1 kHz. To use the described GPA in the UW3D1 transceiver (Yu. Kudryavtsev. Tube-semiconductor transceiver. - “Radio”, 1974, No. 4, p. 22), the 5C23 capacitor is eliminated, the right (according to the diagram) pin 5C24 is connected to the GPA output, and the detuning circuits - with output - 12…24 V GPA.
The thermostat is powered from windings III and IV of power transformer Tr1. Since in the stabilization mode the power consumed by the thermostat does not exceed 1..2 W, the transformer is not overloaded.
Smooth Range Generator
We have come to perhaps the most important stage in setting up the transceiver. This is tuning and setting the frequencies of a smooth range generator (VFO), assembled on an L3 lamp. The stability of the frequency of your radio station on the air almost entirely depends on the quality of operation of this cascade. If the station’s signal “floats” across the frequencies of the range as the case warms up and the transceiver is installed, the GPA is to blame; if on the air you are told that the frequency of the signal from your radio station is “squeezing” or “crying” - the reason is also almost always in the GPA. Therefore, this cascade needs to be given the closest attention. After checking the installation and operating mode of the L3 lamp, you should make sure that the GPA generates high-frequency oscillations. A GIR (heterodyne resonance indicator), a frequency meter or a receiver having a range of 4 - 7 MHz can be useful here. After making sure that the VFO is working (in the case of an auxiliary receiver, set its frequency to 4 MHz and rotate the transceiver’s KPI from minimum to maximum. If, in this case, the VFO signal does not “hung” in the auxiliary receiver set to telegraph mode), you should change the setting of this receiver to the receiving mode at a frequency of 4.5 MHz. Try to receive the VFO signal again. If the next failure occurs, tune the receiver another 0.5 MHz higher. And so on until the VFO signal is detected), determine within what limits it is tuned . Estimate how much these frequency tuning limits differ from the required ones, i.e. from 5.5 MHz to 6.0 MHz with a margin of 20 kHz at the edges. Next, with the GPA still operating at an arbitrary frequency, the current is measured through the Zener diode D1 (KS630A). It should be around 15 - 17 mA. Otherwise, wirewound resistor R45 is selected. Thus, having stabilized the voltage supplying the smooth range generator, we move on to setting it up. It should begin with an external inspection of the GPA, during which it is necessary to make sure that the capacitors C28 and C29, which make up the capacitive “three-point”, are of the SGM or KSO type of group “G”. This is very important, since their instability of capacitance or TKE will affect the overall frequency stability of the generator. The DR6 choke installed in the cathode of the GPA lamp must be of high quality. Its frame should be ceramic, the wire should be laid evenly, with tension, so that it does not have the opportunity to vibrate. This throttle is not impregnated with any glues or resins.- temperature stability will deteriorate, which will inevitably lead to jumps in the GPA frequency. The quality requirements for the VPA contour coil (L19) are well known. This is one of the most important parts of the device. No reels of dubious quality should be used here! You should take the selection of capacitors C27 (120 pF) and C26 (20 pF) very responsibly. As a rule, C27 consists of two capacitors connected in parallel. These are CT type capacitors, one is red or blue and the other is blue. The ratio of their capacitances, giving a total capacitance of 120 pF, is selected using the method of heating the mounting and chassis, which will be discussed below. They begin to lay the boundaries of the frequencies generated by the smooth range generator. As part of this work, it is achieved that with the variable capacitor plates fully inserted, the GPA generates a frequency of approximately 5.480 MHz. If it turns out to be lower, the capacitance of the capacitors that make up C27 must be slightly reduced, if higher, the capacitance must be increased. Initially, when selecting this capacitance, relative attention is paid to the color relationship of its constituent capacitors. With the KPI plates fully removed (minimum capacity), the GPA should generate a frequency close to 6.020 MHz. It is adjusted with a tuning capacitance, structurally installed in the KPI block (it is not shown on the transceiver diagram). After this, the lower limit of the GPA frequency is checked again and adjusted by selecting capacitance C27. And they do this until the GPA begins to operate in the required frequency range, i.e. 5.480 - 6.020 MHz. The VFO frequency is controlled by an auxiliary receiver (excellent if it is a receiver of the R-250 type or similar, with a quartz calibrator and the ability to read the frequency with an accuracy of 1 kHz), or by a frequency meter connected to the L17 coil. However, in the case of using a frequency meter, it is necessary to first adjust the circuit in the anode of the GPA lamp to approximately 5.75 MHz and shunt it with a resistor R14 - 1.2 kOhm. After setting the VFO frequencies, this circuit should be unshunted again and adjusted more precisely to a frequency of 5.75 MHz, and then shunted again. This shunting with a resistor is necessary so that the frequencies from 5.5 to 6 MHz generated by the VFO are supplied to the transceiver mixer with approximately the same amplitude over the entire range, without restructuring the anode circuit. Very often, if not always, a radio amateur has a problem that the VFO covers a frequency range that is larger than required, or, conversely, does not cover the required section. This depends on the ratio of the maximum capacity of the KPI to its minimum capacity, as well as on the value of inductance L19 and capacitance C27. Moreover, if the transceiver uses the KPI required by the author, then insufficient overlap (at imaginable values of C27) indicates an excess inductance of the L19 coil, and vice versa. The required value of inductance L19 should be clarified by selecting the top tap according to the tap diagram, and not only the turn, but even part of the turn plays a role. However, under no circumstances should a regulating core be used to increase the inductance in this coil - the frequency stability will sharply deteriorate. However, this is a problem for those who try to adapt an inductance other than that recommended by the author to the L19 coil. Having completed the installation of the frequency range of the GPA, we begin thermal compensation of this generator, which consists in selecting the ratio of the capacitances of the red and blue colors that make up capacitance C27. This work is carried out using the previously mentioned HF receiver, or using a frequency meter with a frequency measurement accuracy of no worse than 10 Hz. Before working with a receiver or frequency meter, they must be well (2-3 hours) warmed up. The transceiver turns on and warms up for 10 - 15 minutes. If the adjustment is made via the receiver, they find the GPA signal over the air, set in the region of 5.75 MHz. As before, the receiver is in telegraph mode. When working with a frequency meter, it is, as before, connected to coil L17. Then, using a table lamp or a medical reflector, slowly heat up the chassis and parts of the GPA. Moreover, it is better to heat them not directly, but in an area somewhat remote from the GPA, located approximately between the GPA and the output generator tube. When the temperature in the GPA area reaches 50 - 60 degrees, note in which direction the GPA frequency has gone. If it has increased, the temperature coefficient of the capacitors of the C27 components is negative and significant in absolute value. If it has decreased, the coefficient is either positive or negative, but small in absolute value. As already noted, KT type capacitors with different dependencies of the reversible change in capacitance with temperature changes are used as C27. Capacitors with positive TKE (temperature coefficient of capacitance) have a blue or gray body color. Neutral TKE for blue capacitors with a black mark. Blue capacitors with a brown or red mark have a moderate negative TKE, and finally, a red capacitor body indicates a significant negative TKE. After allowing the assembly to cool completely, replace the capacitors components of C27, changing their temperature coefficient in the desired direction, but maintaining the total capacity. In this case, you should check the safety of the previously made frequency arrangement. These operations should be repeated until it is achieved that an increase in the GPA temperature by 35 - 40 degrees will cause a shift in the GPA frequency by no more than 1 kHz. This means that the frequency of the transceiver, when it warms up during normal operation, will not drop by more than 100 Hz in 10 - 15 minutes. It is useful to remember the sign of the end of this arduous work: any smooth impact on the generator (such as smooth heating and cooling, smooth approach of a hand or other object to the installation) should cause a response from the generator in the form of the same smooth change in frequency. After the impact ceases, the generator frequency should smoothly return to its original value. No frequency jumps are allowed! A difficult test awaits a radio amateur who has a poor-quality capacitor in his GPA circuit. This is evidenced by sudden frequency jumps during its operation. In this case, you need to be patient and change all the capacitors in the GPA stage one by one, without paying attention to the previously made frequency arrangement. Unfortunately, not all designers are conscientious about performing the work outlined above. The desire to go on air as soon as possible is understandable. However, you need to find the strength within yourself and, even before the first broadcast, prevent as much as possible all possible flaws in the quality of the signal of your future radio station. It’s rare for anyone to disagree with the opinion that listening to compliments addressed to oneself is much more pleasant than countless comments. After completing the work on setting up the GPA, check the effect of the detuning and set its “zero” position. It should be approximately at the middle position of the rotor of capacitor C25. By disconnecting the detuning capacitor, you can roughly calibrate the transceiver scale, which will help with its further tuning. Initial calibration is performed every 50 kHz. It should be possible to take readings both from the beginning of the scale and from its end, since on the 80 and 40-meter ranges the frequency reading starts from one end of the scale, and on the other ranges - from the other.
Crystal oscillator
The next stage in setting up the transceiver is setting up the crystal oscillator (CH). After checking the installation and operating mode of lamp L2, temporarily remove all quartz from the holders and instead install capacitors with a capacity of 100 pF on the ranges of 28 and 21 MHz, and 300 pF on the rest. The transceiver range switch, which we had not yet used by this time, is set to the 21 MHz range. By changing the tuning frequency of circuit L15 with the core, the generator is tuned to a frequency of 15 MHz. It is controlled by a receiver over the air, or a frequency meter connected to coil L16. Next, changing the position of the transceiver range switch, set the CG frequencies: at 3.5 MHz - 10 MHz, at 7 MHz - 13.5 MHz, at 14 MHz - 8 MHz, at 28 MHz - 22 MHz, at 22.5 MHz - 22.5 MHz. After this, the quartz is installed in its place and once again, within small limits, the anode circuits of the CG lamp are adjusted on each of the ranges to achieve the maximum amplitude of the generated frequency. The voltage is measured with a high-resistance voltmeter (or RF probe) at the cathodes of the mixer lamps. It should be within 1 - 2 Volts. However, you should not despair if at 28 or 28.5 MHz (according to the position of the range switch) the voltage is less than 1 Volt. It depends on the activity of the quartz. But insufficient amplitude of the signal from this generator on any of the bands will subsequently lead to insufficient power of the transceiver, which, of course, is highly undesirable. Having made sure that the CG operates stably on all ranges, it is necessary to once again measure the current through the zener diode KS630A (D1) and, if necessary, adjust it, now to a value of 20 - 24 mA, after which we consider the issue of stabilizing the voltage supplying the transceiver generators resolved . It is very important! It should not be forgotten that interference in cascades powered by a voltage stabilized using zener diode D1 can disrupt stabilization, since this zener diode (like any other) provides stabilization only with certain currents flowing through it. However, it happens when amateurs “attach” additional cascades to this zener diode, for example, modernization, as a result of which at certain moments (when operating in transmission) the current through D1 stops and there is no stabilization. Correspondents report "crying" of the signal. Some people in this case further increase the initial current through the zener diode, reducing R45. But then the interval of mains voltage drops, at which stable operation of the generators is ensured, is reduced. By the way, we have come across cases of connecting UW3DI to the network through a television ferroresonant stabilizer. :-)
Focused selection filter
The next stage is setting up and pairing the contours of the concentrated selection filter. There is no need to stop at setting up the mixer on the 6N23P lamp, because with error-free installation and the presence of anode voltage, it works normally. The essence of tuning a concentrated selection filter (FSS) is that all three circuits that make up the filter coincide in frequency tuning with each other at any position of the variable capacitors located on the common axis of the block of variable capacitors (CCU). This is achieved by installing the same capacitances of each section of the capacitor block at the highest frequency of the range and the same inductances of the coils L29, L30, L31 at the lowest frequency of the range. The first is carried out by selecting the values of tuning capacitors in each section of the KPI (combined structurally in the KPI housing), and the second by selecting the positions of the coil cores. Inductors L29, L30, L31 are made on the basis of SB1A cores. The cores must be new (grayish in color), and the coils must have maximum quality factor. There is experience in using SB2 cores instead of SB1A, but this does not provide a noticeable advantage, such as, for example, the use of inductors based on ring HF ferrites. It is a pity that their inductance cannot be changed smoothly, i.e. It is impossible to achieve high-quality pairing, or rather it is possible, but very difficult. At the same time, you should beware of the mistake that is sometimes made by inexperienced radio amateurs who believe in the “miraculous power” of ferrite cores. Yes, by using ferrites they achieve an increase in the level of the IF signal for transmission, which leads to a slight increase in the power of the transceiver. However, not being able to achieve a clear pairing of inductances (there is no possibility of adjusting them), they, using the original placement of the coils, involuntarily increase the coupling between the FSS links, worsening the most important characteristics of the transceiver when operating in receive mode.
Microphone amplifier
The operation of the microphone amplifier is checked. The easiest way to do this is by disconnecting the lower end of capacitor C103 from the switch according to the diagram and connecting it to headphones, which have their second contact on ground. After speaking a few words into the microphone, make sure that they are reproduced loudly and clearly enough on the phones.
Do not forget that the microphone in tube amplifiers is used with a higher output impedance (at the end of its marking there is the letter “A”, for example, MD201A). If it turns out that the microphone amplifier does not work, you should check its installation and lamp mode. The experience gained from setting up previous cascades will tell you how to proceed. During this work, the voice control system on the L14 lamp is temporarily turned off.
To work with low-impedance microphones, you need to add a cascade on transistor VT1 (Fig. 4). VOX, AntiVOX systems and VL14 lamp are excluded. The right-hand terminal of capacitor C 105, which is freed in the diagram, is connected to the common wire, as shown in Fig. 4. The right terminal of resistor R87 in the diagram is connected to a bus that connects the cathodes of lamps used only in transmission mode. Variable resistor R5 regulates the level of the output signal of the microphone amplifier.
DSB driver
Having configured the microphone amplifier, connect the capacitor C103 in place, turn off the microphone and temporarily “ground” the microphone input. Check the installation and operating mode of the L12 lamp. A high-resistance voltmeter (HF probe) is connected to the anode of the L12 lamp. Having turned on the “Transfer” mode, select the position of the potentiometer R83, achieving minimum voltmeter readings. Having achieved this, they try to change the capacitance of capacitor C88 in both directions from its nominal value. If a change in this capacitance causes a further decrease in the voltage at anode L12, a new capacitance is left, achieving an even greater reduction in voltage by positioning the potentiometer R83. In this way, the smallest remaining HF voltage is achieved at the anode of the L12 lamp. Balancing can be considered complete if the value of the unbalanced carrier residue at the anode does not exceed 0.2 - 0.3 Volts. You may have to select diodes D3 - D6. This can be done using the device described in the chapter "Simple devices for tuning the transceiver". By “ungrounding” the microphone input and connecting the microphone, you should make sure that talking into the microphone causes the voltmeter readings on the L12 anode to increase to 20 - 30 Volts. This indicates proper operation of the balanced modulator and a well-formed two-way signal with a suppressed carrier. This signal will turn into a single-sideband signal after passing through an electromechanical filter (EMF). The input and output windings of the EMF, together with capacitors C89 and C98, should resonate at a frequency close to 501 kHz. This is achieved by selecting the specified capacitors (tuning ones are often installed instead) for the maximum amplitude of a single-sideband signal. This maximum is not very pronounced. The voltage is measured with an RF voltmeter on the anode of the right half of the 6N23P lamp in the “SSB Transmission” transceiver mode when a signal with a frequency of 1 kHz and a level of up to 100 millivolts is applied to the microphone input. The voltmeter is then transferred to the hot end of coil L34. At this point, the level of the generated signal should be about 1 Volt at any position of the main control unit of the transceiver. If you have something, you can try to listen over the air to a single-sideband signal formed and sent to a frequency of 6 - 6.5 MHz, which, by mixing with the frequencies of a quartz oscillator, remains to be brought to the frequency of one or another amateur band, amplified and sent on the air.
Output stage
The output stage of the transceiver is without any special features. Sometimes one encounters complaints about the lack of smooth adjustment of the communication capacitance with the antenna. But shortwave antennas are used, as a rule, constant, with a known input impedance (usually 50 or 75 Ohms). It is better to select constant capacitors C53 - C57 by loading the transceiver onto a non-inductive resistance of the appropriate rating. You can use a 127V 100W electric lamp. As a last resort, selection is made directly to the antenna. When selecting capacitances C53 - C57, it is necessary to keep in mind that the maximum level of radiation into the air occurs, as already noted, at this position C58, which ensures a “failure” of the anode current of the output stage. At the same time, this “dip” should be no deeper than 15 - 20% of the maximum deviation of the meter needle observed in this range at an arbitrary position of the C58 rotor. Therefore, if a deeper “dip” is observed in resonance, it is necessary to more carefully select the appropriate constant capacitance from the number C53 - C57. By doing this on the antenna with which the transceiver will be operated in the future, you get rid of the need to smoothly adjust the communication capacity with the antenna. What seemed like a disadvantage turned into an advantage - one less tuning knob! When carrying out these works, special attention is paid, because The output lamp, when high-frequency voltage is applied to its control grid and the anode circuit is not tuned, can quickly fail. It is necessary to constantly monitor the color of its anodes, preventing them from reddening! In some cases, it is useful to use the power control knob included in the UW3DI.Advice from UX0KX: In the power supply circuit of the control grid GU-29, instead of the ceramic capacitor C62, it is necessary to install an electrolytic capacitor of 200 microfarads at 100 volts. With the lamp open, in transmission mode without a carrier, use an oscilloscope to look at the voltage waveform on the GU29 control grid without and with a 200 uF electrolyte. The difference will be big. Without an electrolytic capacitor, the voltage waveform on the GU29 control grid will have the shape of a “saw”, this has a very bad effect on the signal quality, submodulation occurs at a frequency of 50 hertz. With a 200 uF capacitor, the carrier signal at the output of the GU29 is clean and transparent. The difference can be heard very clearly on the control receiver.
Comprehensive transceiver setup
The VFO frequencies by range at an IF of 8865 KHz are listed in Table 1. This table shows the frequencies for one of the options that I used in my transceiver. In this version, the 80M band is combined with the 15M band. Because of this, both ranges are expanded.
You can refuse this compromise and perform the six-band option. Then each range will cover the required frequency band. You can choose a seven-band option, but with the 10M band divided into two sub-bands.
Setting up the GPA does not create any particular difficulties, but it will require some amateur radio skills and appropriate measuring instruments. The generator is excited well. The signal level can be adjusted by selecting the tap of the coil L and capacitance C9. This makes it possible to set the same levels across ranges. At the same time, it is necessary to achieve minimum levels at which generation will still remain. In the AFC circuit, C2 must be selected for each range, according to what is described in the attached instructions for the Makeevskaya TsSh. In the C3 detuning circuit, we select it in the same way according to the desired detuning width of the receiver on each band separately. The coils of the GPA circuits are wound on bakelite frames with a diameter of 9 mm with tuning ferrite cores. The parameters of some main elements of the GPA are shown in Table 2.
| Range (M) | L (mKH) | C5 (Pf) | S11 (Pf) |
|---|---|---|---|
| 160 | 1,5 | 140 | 118 |
| 80 - 15 | 1,4 | 91 | 430 | 40 | 1,3 | 51 | 51 | 30 | 0,87 | 70 | 10 | 20 | 11,5 | 30 | 750 | 10 | 1,2 | 26 | 680 |
To decouple the GPA, unlike the Ural-84, I used one common buffer cascade, made separately in a closed shielded box made of galvanized iron 0.5 mm.
The buffer stage consists of three emitter followers connected in series, with a separate output for the central control. Due to the low level at the GPA output, the cascade was supplemented with a wideband amplifier, which, with selected elements, linearly amplifies in the range of 1.5 - 30 MHz. The amplifier output is loaded with a 470-ohm potentiometer, with which you can adjust the optimal RF signal level for the balanced mixer to 1.5-2V rms. The circuit does not require any special explanation and is shown in Fig. 3.
The receiver detuning unit is built according to a familiar scheme from the Desna transceiver. During operation, the scheme has proven itself well.
The scheme works as follows:
When detuning is disabled, contacts S1 are open. Bases of transistors VT2 and VT3 through R1; VD2; R5; and R6 receive + voltage. VT2 and VT3 are open VT1 is closed. At point 3. voltage is released from the divider of resistors R2 and R3.
When detuning is enabled, contacts S1 are closed. + voltage through R1 is shorted to ground. Bases of transistors VT2 and VT3 via R5; R6 and VD2 are connected to _ voltage. VT2; and VT3 are closed, VT1 will open from + voltage through R8. now at point 3. voltage will be released from divider R2; R4 and potentiometer R7, with which you can smoothly regulate the voltage at point 3. When switching to gear, +13.5 V is supplied to point 4 through VD1; R5 and R6 opens VT2; VT3. VT1 closes. Point 3 is again connected to the divider R2 and R3 and the detuning is disabled.
The only identified drawback of the circuit is the mismatch between the reception and transmission frequencies when the proofing is turned off. I managed to get rid of this by introducing resistor R9
The fact is that when receiving VT2 and VT3 it opens at a voltage of +8V. When transmitting at point 4, a voltage of +13.5V is applied and this causes the transistors to open to a greater extent and the voltage drop across VT3 will be less. Although the difference in voltage at point 3. is insignificant, only about 0.03 V, this is enough to change the frequency in some ranges up to 100 Hz. Resistance R9 must be selected so that at point 4 the voltage is the same during reception and transmission.
The circuit diagram of the detuning unit and the +8V voltage stabilizer is shown in Fig. 4
The +8V voltage stabilizer receives power from a stable +13.5V power source. Thus, double stabilization of the GPA supply voltage is ensured. Resistor R13 sets the current limiting threshold. At the value indicated in the diagram (4.7 ohms), the limiting current is 200mA. The stabilizer parts are placed on the same board with the detuning unit.
The switching unit can be viewed in Fig. 1. It includes a transistor VT1, diodes VD1 - VD5 and resistors R1, R2. It automatically supplies voltage when the band select switch is switched to the corresponding GPA generator and automatically switches the central frequency switch to the + IF position or – IF depending on the range.
The +5V voltage stabilizer is made according to a simple circuit on a microcircuit stabilizer type KR1157EN501A and is placed on the same board with the switching unit. The diagram is shown in Fig. 5.
