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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Pocket SV-radio station. 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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The radio station operates at a fixed frequency of one of the channels in the 27 MHz range with amplitude modulation, has quartz frequency stabilization. Provides a communication range with the same type of radio station up to 2 km in open areas and up to 500 m in the city.

The circuit diagram is shown in the figure. The receiving path is made on two microcircuits A1 (K174PS1) and A2 (K157XA2) according to the scheme with a minimum number of circuits. Switch S1 is shown in the "receive" position. The input signal from the antenna through the switch section S1.1 is fed to the input circuit L1C1 tuned to the frequency of the received channel. The communication coil L2 serves to match the high-resistance unbalanced output of this circuit with the symmetrical low-resistance input of the frequency converter of the A1 microcircuit. The local oscillator is also part of this microcircuit, and it allows using only a quartz resonator as a frequency-setting element without any additional heterodyne coils.

Pocket CB radio
(click to enlarge)

The intermediate frequency is allocated to the mixer load - resistor R1. The role of the selective element is entirely entrusted to the Q2 piezoceramic filter. As a result, the entire receiving path contains only one input circuit. This is very important for a small-sized radio station, since the most labor-intensive and overall element is an inductor with a tuning core. In addition, it is extremely easy to set up.

The IF amplifier, detector and AGC system are made on the A2 - K157XA2 microcircuit, included according to the standard scheme.

From the output of the receiving path, the low-frequency signal through the volume control R7 and the dividing circuit R9C14 enters the input of the ultrasonic frequency converter, made on the K174XA10 chip.

The UZCH input does not switch; when receiving, it receives a signal through R9, and when transmitting through R11 from an electret microphone, which does not receive power when received. And during transmission, power is not supplied to the receiving path (switch section S1.3).

When received from the UHF output, the signal through S1.2 is fed to the dynamic head B1.

During transmission, switch S1 is in the opposite position shown in the diagram. Section S1.3 disconnects power from the receiving path and supplies it to the transmitting path. The transmitter master oscillator is made on the transistor VT1. The oscillation frequency is stabilized by the resonator Q3. In the collector circuit of the transistor, the L3C22 circuit is tuned to the frequency of the resonator. Then, through the coupling coil L4, the RF voltage is supplied to the power amplifier on the transistor VT2. Amplitude modulation is carried out in the emitter circuit of this transistor using a low-frequency transformer T1, which, during transmission, receives a low-frequency signal from the output of the ultrasonic frequency converter on the A2 microcircuit. At the output of the transmitter, a U-shaped circuit C24L5C25 is turned on, followed by an extension coil L6 and an antenna W1.

For winding coils, plastic frames with a diameter of 5 mm are used with carbonyl iron trimmers from armored cores SB-12A. Coil L1 contains 10 watts, L2 is wound on L1, it contains 3 turns. Coil L3 contains 9 turns, and L4 is wound on top of it, it contains 5 turns. These coils are wound with PEV-0,31 wire. The L5 coil contains 5 turns of PEV-0,43 wire, the L6 coil contains 15 turns of PEV-0,31. Choke DL1 - ready, DPM 0,1 at 120 μH.

Quartz resonator Q1 at 27,12 MHz, 02 at 26,655 MHz. Piezoceramic filter at 465 kHz. Transformer T1 is an output transformer from the old Selga-405 receiver, it has a small-sized W-shaped core. Its winding 1 contains 300-500 turns of PEV 0,1, winding 2 - 50-100 turns of PEV0.2.

Antenna - telescopic from a radio receiver with a VHF band.

Electret microphone MKE-3. Switch S1 - P2K without fixation. Dynamic head 0.2GD-1, or another small-sized coil with a resistance of 6-10 ohms.

The power of the radio station is 0,25 W., the sensitivity of the receiver is 5 μV / m, the current consumption during transmission is not more than 120 mA, while receiving is not more than 18 mA. Other parameters were not measured.

Literature

  1. Radio station "Chizhik-SV-AM", Radiokostruktor 12-99, pp. 6-7.
  2. Receiving paths of amateur AM MW radio stations, Radioconstructor No. 06 1999, pp. 25-32.

Author: Timoshenko P.V.; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Civil radio communications.

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