RELM RPU416, Руководство пользователя, Страница: 7 / 39

RPV516/RPU416 Circuit Description
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5) Squelch
Part of the AF signal from IC200 re-enters IC200, and the noise component is amplified and rectified
by a filter and an amplifier to produce a DC voltage corresponding to the noise level.
The DC signal is injected to the analog port of the microprocessor (IC403). IC403 compares the
voltage with the preset value and determines whether to output sounds from the speaker. IC403
sends a high level signal to the MUTE and AFCO lines and turns IC302 on through Q302, Q304,
Q305, Q306 and Q307. (See Fig.3)
FM IF IC200
IF AMP DET
DET HPF
AMP
IC 300
AF AMP LPF HPF
Q302
SW
IC302
AF/PF AMP
Q307
SW
SP
Q304.Q305.Q306
SW
Q15
W/N SW
IC301
LPF
5 62 67 6
BUSY MUTE AFCO TI
IC403
MPU
Fig. 3. AF amplifier and squelch
6) Receiving signaling
CTCSS/CDCSS
IC200 output signal is filtered by 300Hz low-pass filter (IC301) and the filtered signal is input to the
microprocessor (IC403). IC403 determines whether the CTCSS or CDCSS matches the preset value,
and controls the MUTE and AFCO and the speaker sounds output according to the squelch results.
TTS
IC200 output signal is filtered by IC8 and then applied to the microprocessor (IC403). IC403 compares
TTS with the preset value and controls MUTE and AFCO and speaker output according to squelch
results.
3. PLL frequency synthesizer
PLL circuit generates the first local oscillator signal for reception and the RF signal for transmission.
1) PLL
The frequency step of the PLL circuit is 2.5 or 6.25KHz. A 12.8MHz reference oscillator signal is
divided at IC1 by a mixed counter to produce 2.5 or 6.25KHz reference frequency. The voltage
controlled oscillator (VCO) output signal is buffer amplified by Q6, and then divided in IC1 by a
dual-module programmable counter. The divided signal is compared in phase with the 2.5 or 6.25KHz
reference signal in the phase comparator in IC1. The output signal from the phase comparator is
filtered through a low-pass filter and passed to the VCO to control the oscillator frequency. (See Fig. 4
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