Transceiver prefix to the radio receiver Katran (R-399). Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Transceiver prefix to the radio receiver Katran (R-399). 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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Many radio amateurs would like to use "Katran" in transceiver mode. In the proposed design, the goal was to create a prefix with minimal alterations in the receiver itself. Schematic diagram of the attachment is shown in Fig.1-3.

Fig.1 (click to enlarge)

For the operation of the set-top box, only the signals of the receiver's local oscillators and a signal to control the "half-duplex" mode (locking the receiver's IF path when switching to transmission) are needed. The signal from a microphone amplifier assembled on a 122UN1A chip is fed to the input of a balanced modulator. A signal with a frequency of 213,5 kHz or 216,85 kHz (depending on the selected sideband) from the receiver also comes there. The generated DSB signal is fed to a DSB amplifier assembled on a KP350B field-effect transistor.

The load of the amplifier is an electromechanical filter with a bandwidth of 3 kHz. The SSB signal is amplified by a two-stage amplifier and fed to a double balanced mixer assembled on low-noise KT368A bipolar transistors. The signal of the second local oscillator of the receiver, additionally amplified and filtered, also comes here. The difference frequency signal is separated by a four-loop bandpass filter and fed to a passive double balanced mixer. The frequency synthesizer signal is also pre-amplified. The LPF filters out components above 67 MHz. A push-pull emitter follower is used to match the low input impedance of the diode mixer and the low-pass filter. The radio signal from the mixer output goes to the block of bandpass filters (Fig. 2), which provide the necessary signal filtering.

Transceiver prefix to the radio receiver Katran (R-399)
Ris.2

Then the signal is amplified to a level of 15-20 V by a transistor circuit (Fig. 3) and fed to the final stage assembled on a GU-19 lamp.

Fig.3 (click to enlarge)

Range switching is performed by pressing the buttons of the quasi-sensor range selector (Fig. 4).

Fig.4 (click to enlarge)

In the low-signal part, the RES-49 relay is used, and in the P-circuit - RES-47. When working with the set-top box, the "Half duplex" switch on the front panel of the receiver should be switched to the on state. This provides "locking" the IF path during transmission. Setting up the set-top box will not cause difficulties, since many nodes have been repeatedly used in radio transmitting technology and methods for their adjustment have been given.

I would like to draw attention to the setting of the amplifier of the second local oscillator 35 MHz and the frequency synthesizer amplifier. Adjustment is best done using a frequency response meter. Setting up a 35 MHz local oscillator amplifier comes down to setting up a low-pass filter, the data of which is taken from the Katran product description. Setting up the synthesizer amplifier comes down to setting the low-pass filter and ensuring the uniformity of the frequency response of the amplifier in the range of 36-67 MHz. The output voltage of the synthesizer amplifier is Uout = 3 V. The power supply has no special features, therefore it is not shown in this diagram. Tp1-Tr3 are wound on rings 1600 mm K 7x4x2 in three wires of 8 turns, Tr5-Tr6 - on the same rings, but 10 turns each, Tr4 - 50VCh K 7x4x2 in two wires of 7 turns.

It should be noted that the 35 MHz band-pass filter suppresses the first conversion image channel separated by 40 fIF = 2 kHz by at least 430 dB. Otherwise, your TX will not meet the requirements of the GIE. Coils and filter capacitors must have a maximum quality factor. In case of difficulties with the required suppression of the image channel, it is recommended to add another 1-2 circuits, compensating for the losses with an additional amplifier, similar to the buffer frequency amplifier of the first local oscillator.

Literature

1. Golovin O.V. Professional decameter radio receivers. - M.: Radio and communication, 1985.
2. Lapovok Ya.S. I am building a KB radio station. - M.: DOSAAF, 1983.
3. Red E.T. Circuitry of radio receivers. Per. with him. - M.: Mir, 1989.
4. Red E.T. Reference manual for high-frequency circuitry. Per. with him. - M.: Mir, 1990.

Author: A. Samoylenko (UW0LFY), Arseniev, Primorsky Krai; Publication: N. Bolshakov, rf.atnn.ru

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