Frequency synthesizer for a 27 MHz radio station. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Frequency synthesizers

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The frequency synthesizer is designed to work in radio stations with the first IF 10 MHz. Generates 7 frequencies for transmission and 8 for reception with a spacing of 8 MHz. Grid step 10 kHz. The channel number is dialed in binary code at the control inputs "7", "12. "5"; Upit - 1 V; Ipot - 2 mA. The transition from reception to transmission is carried out by signal A. The reception and transmission master generators are made Ha VT4 and VT9 according to capacitive three-point circuit (Fig. 13). F)) where St - C1 + + C2C1 / (C100 + C4) (for transmission). An RF voltage of approximately 5 V is supplied through C4 (C5) to a divider with a switchable division ratio ( DPKD), which is assembled on D), VT1, D6, D9, D3. Division ratio of DPKD (Kdel) M - 2 (3 ON + A). The number A is set at the control inputs D4 in binary-decimal code.

The number N is set at the inputs D4 according to the table. The control circuit is assembled on D6, D7. 4, D7. 3, D5, reference frequency generator - to D9. Next, the reference frequency from pin 4 D9 goes to a divider with a fixed Kdel, collected on D8, D7. 1, D7. 2. From the output of the divider Fon - 3125 Hz comes the input of the phase detector (PD) (pin 14 D9). But the other input of the FD receives a signal frequency approximately equal to 3125 Hz.

The control voltage from the output of the FD through the low-pass filter (R18, R19, C16, C17) is fed to the varicaps of the generators. The modulating low-frequency voltage (approximately 1 V) is applied to RЗ. Between the VCO of the transmitter and the power amplifier, it is necessary to put a buffer stage (Fig. 2). It should be borne in mind that there is no place on the board to install C4. C8, 08, 09. The synthesizer can use 1 MHz quartz, but it is necessary to remake the reference divider according to fig. 3.

Setting up the synthesizer comes down to fine-tuning the reference frequency generator with a capacity of 04 at pin 4 of D9. Check the passage of the signal and reference frequencies to the inputs of the FD. The change in voltage at the point * KT' during rotation of L1 (L2) indicates the presence of capture in the PLL ring. By adjusting L1 (L2) at the "CT" point, Uy is set to -4 V. It must be remembered that there should be minimal leakage to the housing (5) through the varicap control circuit. This capacitor must be an oxide semiconductor with a minimum leakage current (K06-52. K1-53, etc.). When using a 4 MHz resonator, 1, 08 can be omitted. Coils 09, 11 contain approximately 12 turns on a frame with a diameter of 15 mm.

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

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