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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Radio Pilot. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio stations, transceivers Despite the relatively small dimensions and weight, this MW (27 MHz) FM radio station has a receiver sensitivity of 0,15 μV and a transmitter output power of 1 ... 1.5 W (with a 9 V supply). The most significant difference from most radio stations of a similar class is the continuously adjustable noise reduction system. "PILOT", of course, has its drawbacks. This is, first of all, the relatively low selectivity of the receiver in the adjacent (40 dB) and side (30 dB) channels, which is determined by the parameters of the intermediate frequency filter (465 kHz). The squelch control is also a sensitivity control. The level of noise heard in the loudspeaker decreases smoothly, which gives certain benefits: - provides the ability to use the volume control and noise suppressor to set the maximum sensitivity at an acceptable noise level;
The "PILOT" is powered by a voltage of 6,3 ... 12 V, consuming no more than 10 mA in the standby reception mode. When transmitting, the current consumption is about 300 mA (at a power of 1 W). The current consumption data is given at a nominal supply voltage of 9 V and with an antenna dummy.
The input signal (Fig. 1) from the antenna through the contacts of the switch SB1.2 (reception / transmission) is fed to the input of a radio frequency amplifier (URCh), made according to a cascode circuit on transistors VT1, VT2. From the URF output, the signal is fed to the mixer input (to the VT3 base). The emitter VT3 receives voltage from the coupling coil of the local oscillator circuit assembled on VT4. The operating point of the mixer transistor is determined by detecting the local oscillator voltage. From the output of the mixer, the intermediate frequency voltage (465 kHz) is fed through the piezo filter to the input of the DA1 microcircuit. In the microcircuit, the IF signal is amplified by a limiting amplifier (MA) and demodulated by a frequency detector (FR). The output voltage of the latter is supplied to the volume control RP1 and, in parallel, to the non-inverting input of the operational amplifier (op-amp) as part of DA1, which acts as an RF filter amplifier for the noise suppressor. From the volume control engine, the signal comes to an audio frequency amplifier (UZCH), made on an operational amplifier DA2 and transistors VT6, VT7 (output stage), the output of which is loaded on the B2 loudspeaker (50 ohms). If there is no signal at the receiver input, there is a maximum noise level at the BH output, which is amplified by the op amp and fed to the rectifier (VD2, VD3). The load of the rectifier is the RP2 noise reduction level regulator, from the engine of which a constant voltage is supplied to the base of the VT5 analog switch. An open transistor shunts the UZCH input through capacitor C28. When a signal appears at the receiver input, the noise level at the FH output decreases, respectively, the degree of shunting the UHF input by the VT5 transistor decreases, which shunts not only the UHF input, but also the FH output through R23. This leads to a decrease in the DC voltage opening VT5. Due to this feedback, smooth operation of the squelch is achieved. By the way, it is easy to turn the noise suppressor into a threshold one by replacing C28 with a 10 ... 100 kOhm resistor. The master oscillator (MG) of the transmitter is made on a VT8 transistor with frequency stabilization by a ZQ3 quartz resonator operating on the fundamental harmonic. This choice is determined by the need to obtain sufficient deviation (1,5...2 kHz). The ZG signal is amplified in power by two stages (VT9, VT10). These transistors operate in a key mode. The output voltage harmonics are filtered by a U-shaped filter (C50, 18, C53), which also matches the output impedance of the cascade on VT10 with the transmitter load (500m). The series resonant circuit (C52, L9) is used for better suppression of the 2nd harmonic. Operational amplifier DA3 is a microphone amplifier-modulator. Its output voltage is supplied to the VD8 varicap, included in the oscillatory circuit of the ZG. The DA3 power supply is stabilized to maintain a constant varicap bias voltage, which is exactly half the DA3 supply voltage. The trimmer resistor RP3 adjusts the gain of the modulator. The frequency response of the modulator is formed by two chains - C39, R36 and C42, RP3. To the inverting input of DA3 is connected the output of the tone-call signal generator, which is assembled on the DD1 chip. The signal consists of bursts with a frequency of about 2500 Hz, with a repetition rate of about 400 Hz. Such a signal is well understood even with a small signal-to-noise ratio. Power is supplied to the DD1 chip through the contacts of the SB2 button. The VD6 LED, which is structurally located under the power switch slider, is connected to the power supply of the transmitter through the VD5 zener diode and the R34 resistor. This indicator lights up in transmit mode until the battery voltage drops to approximately 6V.
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