Modern car-stationary radio station. Scheme, description

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Modern car-stationary 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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Schematic diagram of the 27 MHz radio station is shown in Figures 1 and 2.

Circuit diagram (1)
Circuit diagram (2)

Technical specifications

Pout 15...17 W
Supply voltage 12...13,5 V
Number of channels (European and
Russian mesh)90+90
Type of radiationF3E (FM)
Frequency range 26965...27855 kHz
Sensitivity at S/N ratio 12dB 0,3 µV
Selectivity for all side effects
channels, not less than 60 dB
Selectivity for neighboring
channels, not less than 80 dB
Frequency tuning time, no more than 100 ms

In receive mode, the station operates as follows. The signal received by the antenna passes through the current transformer Tr1 and low-pass filter, consisting of elements C19, L8, C18, L7 and part of the capacitance C24, then passes through a band-pass filter, consisting of two coupled circuits formed by elements C24, C25, L9, L10, C26, C27, C28. Diodes VD13, VD14 perform a dual role. Firstly, they protect the input of the receiver in transmit mode, and secondly, they connect the C25 to the case.

Thus, in the capacitance transfer mode, C24, C25 can be considered connected in parallel. Next, the signal goes to the URF, included in the scheme with ABOUT, which has a greater linearity. The URC load is circuit C31. C32, L14. Diodes VD15, VD16 protect the mixer in transmission mode. The mixer is assembled on a field-effect transistor VT10.

The local oscillator voltage is removed from part of the L13 coil and fed through the elements R37, C33, R38 to the source VT10. The mixer load is an oscillatory circuit tuned to a frequency of 10695 kHz. The first local oscillator is assembled on VT14 according to the OK scheme. The control voltage is supplied to the VD 17 varicap. From the voltage divider R61, R62, the high-frequency voltage is supplied to the input of the DPKD (pin 41) of the DD2 microcircuit. The signal of the first IF is then fed to the input of the buffer amplifier assembled on VT11. This amplifier decouples the mixer and the ZQ1 crystal filter. The ZQ1 filter is a 4th order monolithic crystal filter with a bandwidth of about 8 kHz. Resistor R44 partially serves as a load for filter ZQ1.

Then the signal goes to the second mixer, located in DA1. In this design, the MC3362 is used as a receiver with a single frequency conversion. The use of the MC3362 (as well as other single-chip narrow-band receivers with two frequency conversions) with a quartz filter in double frequency conversion circuits is impractical, because crystal filters are quite large, and the input and output pins of the MC3362 for connecting the filter are located nearby. Therefore, a sufficiently strong electrical coupling occurs, and the characteristics of the crystal filter cannot be fully realized. On the other hand, the linearity of single-chip receivers leaves much to be desired.

All further processing and signal detection is carried out in DA1. R45 is a squelch (Squelch) level control. Signal detection is carried out using a ZQ3 phase-shifting ceramic resonator at a frequency of 455 kHz. If the SHB is closed, in this mode it is possible to scan through the channels until the carrier is detected. At the moment the carrier is detected, the voltage at point 9 drops to zero, and the scanning stops. - to the volume control R13.

The transmitter signal exciter (VCO) is assembled on a transistor VT1 according to the circuit with OK. The modulating low-frequency voltage is supplied to the anode VD1. The exciter is turned on by the VT2 key. The elements VD1, C2, C3, L1, C5, C6 are frequency-setting. From the output of the exciter, the signal is fed to the buffer amplifier VT3. Elements R12, R13, R14, VD2, VD3 form a switch that provides reliable isolation of the exciter from the transmitter power amplifier. The switch passes the signal to the PA only when the transient ends in the PLL loop.

The first stage of the FM is assembled on VT4 according to the OE scheme and operates in mode A. The elements L2, C 10 form a resistance transformer between the output resistance VT4 and the input VT5. Between the cascades VT5, VT6 there is a resistance transformer, consisting of cascaded circuits 1-3, C12 and C13, L4 L5 and part of the capacitance C24 transform the output resistance VT6 into a resistance of 50 ohms.

(click to enlarge)

A small part of the transmitted power is rectified by the diodes VD4, VD5 and fed to the VD12 LED, which serves as an indicator of the transmitter's operation.

Further, the signal passes the low-pass filter and the current transformer Tr1.

On the elements R23, C21 C20, Tr1, VD7, VD8, C22, R25, a mismatch control circuit in the antenna is assembled.

The greater the level of mismatch in the antenna, the higher the level of DC voltage at point 4. Thus, by controlling the voltage at point 4, you can adjust the antenna of the radio station. If the mismatch is large (for example, an antenna break), VT7 opens. The trigger assembled on the elements DD1 3, DD1 4 is transferred, VT8 closes, the VD12 LED lights up. The exciter signal no longer arrives at the input of the power amplifier. If such a situation occurs, you must immediately turn off the station. Elements C23, R27 are used to set the trigger to its original state.

In transmission mode, the dynamic head B1 is connected to point B, transistors VT13 VT15, VT16 are closed, and VT12, VT17 are opened.

In the TX mode, the control buttons S1 S6 are blocked.

The amplifier-limiter and low-pass filter of the microphone signal are assembled on DA3.

Synthesis of frequencies and control of all modes of the station is carried out using the LSI DD2. The reference oscillator 10240 kHz (ZQ4) is simultaneously the second local oscillator of the receiver. A detailed description of the operation of DD2 can be found in [2]. Button S1 - turn on scanning (only possible in the closed NR mode), S2 - switch to the range indication and back, button S3 - move down the channels (ranges), S4 - move up the channels (ranges), S5 - switch to channel N9 , S6 - grid change "0/5".

The lower decimal point of the H1 indicator is the PLL ring lock indicator. With the correct operation of the ring, it is extinguished.

The station is powered by a stabilized source with an output current of at least 3 A.

Literature

1 Radio amateur, 1996, N10
2 Radio amateur, 1998, N2
3 Radio amateur, 1998, N9
4 Radio amateur, 2000, N2
5 Manasevich V. Frequency synthesizers - M Communication, 1979

Author: V. Vasiliev, Orenburg; Publication: N. Bolshakov, rf.atnn.ru

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