RCA BR200DV, Service Manual

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BR200DV/BR300DV
Service Manual
26
distortion in case of oversized MIC signal.
Q601, the power switch of voice processing circuit, controlled by MCU, will give power supply to IC601
only during transmission.
J501 is the socket for external MIC, and the internal MIC will disconnect automatically when using
external MIC, but the internal PTT is still effective.
5.4 PLL Frequency Synthesizer
Figure 7 Schematic Diagram for Frequency Synthesizer
The DR6000-1 adopts PLL frequency synthesizer.
Frequency synthesizer consists of reference oscillator, voltage controlled oscillator (VCO),
programmable frequency divider (PFD), phase comparator and low pass filter (LPF).
RX VCO Unit consists of Q3 D1 D3 L13 C34 C38 C39 and C42.
TX VCO Unit consists of Q4 D2 D4 L14 C35 C41 C44 and C45,D5 is the modulation circuit of VCO.
IC607 (SKY72310) is PLL integrated circuit and contains programmable parametric frequency divider
(PPFD), programmable frequency divider (PFD), phase comparator and charge pump, etc.
Low pass filter consists of R5 R7 R9 R10 C12 C15 and C18.
Reference frequency is provided by X1 (TCXO, 16.8MHz).
Reference frequency of TCXO (Temperature-controlled Crystal Oscillator) is divided by PPFD in IC607
to produce reference frequency of 5kHz or 6.25kHz (controlled by MCU based on the set channel
frequency).
The oscillation frequency of VCO is compared with reference frequency to produce error signal after
divided by PFD in IC607. The error signal is filtered by low pass filter before changing the VCO
frequency to the set value in VCO (it is locking).
N=F
VCO
/F
R
N ： Division Frequency
F
VCO
：
VCO Oscillation Frequency
F
R
： Reference Frequency