Transceiver Donbass-1M. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Transceiver Donbass-1M. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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According to on-air estimates, tube transceivers continue to be popular with radio amateurs from the CIS. The proposed device was designed to operate on low-frequency bands (160 - 30 m). The option described below is for SSB and CW operation on the 160m band.

The transceiver is built according to the scheme with one frequency conversion (IF 500 - kHz). The sensitivity of the receiving path is not worse than 5 μV. The dynamic range for intermodulation of the third order is not less than 80 dB. Selectivity at a detuning of ± 10 kHz "80 dB. The output power of the transmitter with a load resistance of 75 Ohm -10 W (with an output stage supply voltage of 250 V).

The circuit diagram of the transceiver is shown on pic.1 и pic.2

In the receive mode, the signal from the antenna through the attenuator, made on the resistor R35, and the band-pass filter L9C34C35C36L10 is fed to the left lamp triode VL5 according to the scheme. From it, it is fed to a broadband ring diode mixer, assembled on transformers T2, T3 and diodes VD3 - VD6. The voltage from the smooth range generator also comes here.

The GPA is assembled on a VL6 lamp according to the inductive three-point scheme. With a variable capacitor C47, the transceiver is tuned in range. Resistor R45 can detun the receiver within +/-5 kHz relative to the transmit frequency. Trimmer resistor R46 sets zero detuning.

The converted signal is fed to the input of the first stage of the IF amplifier, assembled on the left according to the VL7 lamp triode circuit, connected according to the common grid circuit, and then through the electromechanical filter Z1 (in SSB mode) or Z2 (CW) - to the control grid of the VL3 pentode, on which the second cascade of the IF is performed. Its anode circuit includes the L6C21 circuit of a multiplier-type detector-modulator on a field-effect transistor VT1. The Z3 filter selects a low-frequency signal, which is amplified by a two-stage low-frequency amplifier assembled on a VL4 lamp. In the receiving path, the gain is controlled by the IF with a variable resistor R15.

When transmitting in SSB mode, the signal from the microphone is fed to the transmitter's low-frequency amplifier (on the VL9 lamp triode on the right according to the scheme), and then through the cathode follower on the VL9 right triode and the Z3 low-pass filter to the modulator detector (VT1, L6, L7). The DSB amplifier is made on the VL7 triode. The SSB signal from the output of the EMF Z1 through the cathode follower on the right triode VL5 comes to the broadband ring diode mixer (on the elements T1, T2, VD3 - VD6). From the mixer, the signal is fed to the input of the first transmitter amplifier (the right triode VL5), made according to the common grid scheme. The operating frequency signal allocated by the L11C42 circuit is first amplified by the pre-terminal stage (at the VL2 pentode), and then by the output stage (on the VL1 lamp), to which the C1C2L1C3C4C5 P-circuit is connected. Resistor R13 regulate the output power of the transmitter.

In CW mode, switch S1 removes the anode voltage from both halves of the lamp in the transmitter's low-frequency amplifier and feeds it to a CW-controlled amplifier with a common grid on the left VL8 triode. A voltage with a frequency of 500 kHz is supplied to its cathode circuit from a quartz local oscillator (assembled on the right VL8 triode). From the output of the controlled amplifier, the signal through the capacitor C68 and the contacts of the relay K2 is fed to the grid of the right triode VL7, which is connected according to the cathode follower circuit. The further passage of the CW signal coincides with the passage of the SSB signal.

To switch from reception to transmission, a voltage of -4 V is applied to the control grids of idle lamps through the contacts of relay K70 (-70 V RX in receive mode, -70 V TX in transmission mode).

The transceiver does not contain particularly scarce parts. The contour coils are made on frames with a diameter of 7,5 mm (from old TVs) and contain 32 turns of PEV-2 0,24 wire. Coil L8 has 4 turns. The coil in the GPA is wound on a textolite frame with a diameter of 20 mm (20 turns) with PEV-2 0,7 wire. The tap is made from the 5th turn, counting from the pin connected to the body. Coil L1 is made on a textolite frame with a diameter of 40 mm and contains 50 turns of PEV-2 1,0 wire. Choke L2 contains 10 turns of PEV-2 1,0 wire wound on resistor R13, L3, L4 - D-0,1.

Broadband transformers T2, T3 are made on ring (with an outer diameter of 12 mm) ferrite magnetic cores with an initial magnetic permeability of 1000 ... 2000. Winding is carried out with three weakly twisted wires PELSHO 0,33. The number of turns is 12.

Low-pass filter Z3 - D-3,4. It can be replaced with any other (including home-made) low-pass filter with a cutoff frequency of about 3 kHz. In extreme cases, it (as well as resistor R27 and capacitor C27) can be excluded.

If necessary, the detector-modulator on a field-effect transistor VT1, which provides carrier suppression by 30 ... 40 dB, can be replaced with a "classic" ring balanced diode modulator-detector.

Relay K1, K4 - RES-9 (passport RS4.524.200), K2, K3, K5 - K8 - RES-10 (RS4.524.302). The output stage uses KPIs from old tube receivers. Capacitor C3 is isolated from the chassis. In the GPA, one section of the KPI from the VEF radio receiver is used.

The transceiver power supply must provide +300 V (300 mA), +100 V (stabilized, 50 mA), -70 V (50 mA), +24 V (500 mA), AC 6,3 V (3 A) and 12,6 V (1 A).

Chassis and front panel sketches are shown on pic.3 и fig.4.

The transceiver begins to tune with the GPA by "laying" the frequency within 2330 ... 2430 kHz, selecting capacitors C48, C52. The overlap frequency is controlled by a frequency meter. To do this, open the circuit between the resistor R52 and the capacitor C56 and connect the frequency meter probe to the latter. The frequency of the GPA can also be controlled by a receiver with an appropriate range. The effective value of the RF voltage across the capacitor C56 must be at least 1,5 ... 2,5 V. Then the operation of the quartz local oscillator is checked. The RF voltage across capacitor C77 must be within 1...2:V.

Convinced by traditional methods of the performance of the AF amplifier, they proceed to the establishment of an intermediate frequency amplifier. Capacitor C59 is disconnected from transformer T3 and through it to the cathode of the VL7 lamp with

the standard signal generator is supplied with a voltage of 500 kHz. Trimmer coil L6 and the selection of capacitors C66, C70 and C67, C71 achieve maximum volume. Then the connection of the capacitor C59 with the transformer T3 is restored and the final adjustment of the receiving path is started. Capacitor C47 sets the GPA frequency corresponding to the middle of the operating range, a signal from the GSS is fed to the antenna input of the transceiver and the coils L9, L10 of the bandpass filter are adjusted to the maximum volume.

Setting up the transmitter begins with checking the operation of its bass amplifier. To do this, a capacitor with a capacity of about 3 microfarads is temporarily soldered between the contacts of the K0,1 relay, a microphone is connected and the signal quality is assessed by ear. Then, having loaded the transceiver on the equivalent of the antenna, the S3 toggle switch puts the Transceiver into transmission mode and the resistor R5 sets the quiescent current of the VL1 lamp to 30 mA. After that, the capacitor C45 is disconnected from the transformer T2 and oscillations with an amplitude of about 0,2 V and a frequency corresponding to the middle of the range are applied to it. By adjusting the coils L11 and L5, they achieve the maximum current ("buildup") of the output stage (about 120 mA). In the case of self-excitation of the cascade, parallel to the coils L11 and L5, resistors with a resistance of 1 ... 10 kOhm should be connected (selected experimentally). Having restored the open circuit, in SSB mode, saying a loud "ah-ah" in front of the microphone, they check the level of "buildup" of the output stage.

Then the transceiver is switched to CW mode and the toggle switch S2 is closed. By selecting capacitor C68, they achieve the same “buildup” of the output stage as in SSB mode. The P-circuit is tuned in the usual way (either using a reflectometer, or by decreasing the current of the output stage lamp (by about 20% at the time of resonance).

Author: Vladimir Gordienko (UT1IA ex RB5IM), Donetsk, Ukraine; Publication: N. Bolshakov, rf.atnn.ru

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