RELM RPU416, Руководство пользователя, Страница: 6 / 39

RPV516/RPU416 Circuit Description
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1-b) Front end RF amplifier (RPU416)
The input signal of antenna is applied to an RF amplifier (Q203) after passing through a
transmit/receive switch circuit and a 3-grade low pass filter. The amplified signal is filtered through a
band pass filter (a 3-grade LC filter) to eliminate unwanted signal before it is applied to the first mixer.
The voltage of varactor is provided by MPU (IC403). (See Fig. 2-b)
B
C C
B
ANT
D102
D103 Q203
RF AMP BPF
L208-L211
MCF
XF201
IF AMP
Q201
MIXER
Q202
CF200
IF.MIX
IC200
AF AMP
LPF.HPF
IC300
AF PA AMP
IC302
SP
WIDE/NARROW SW
Q303 multiply TCXO
1st Local OSC
(PLL)
BPF
L214-L215
MCU
X3
Q1
IC403
APC
TUNE
Fig. 2-b. Receiver section configuration
2) First mixer
The signal from the RF amplifier is heterodyned with the first local oscillator signal from the PLL
frequency synthesizer circuit at the first mixer (Q202) to create a 38.85 MHz first IF (intermediate
frequency) signal. The first IF signal is then applied to two monolithic crystal filters (MCFS: XF200) to
further remove spurious signal.
3) IF amplifier
The first IF signal is amplified by Q201, and then enters IC200 (IF processing IC). The signal is
heterodyned again with a second local oscillator signal within IC200 to create a 450KHz second IF
signal. The second IF signal is then fed through a 450KHz ceramic filter (CF200) to further eliminate
unwanted signals before it is amplified and FM detected in IC200.
4) AF amplifier
The recovered AF signal obtained from IC200 is amplified by IC300 (1/4), filtered by the IC300
low-pass filter (2/4) and IC300 high-pass filter (4/4), and de-emphasized by R303 and C306. The
processed AF signal is then passed to a WIDE/NARROW switch (Q303) and its output is applied to
an AF volume control and is amplified to a sufficient level to drive a loud speaker by an AF power
amplifier (IC302).