RCA BR200D-U1 Service Manual page 23

BR200D-U1/BR300D-U1 Service Manual
C255 C260 L211 L209 L208 D201 D202 and D204 via RX/TX switch (D101 D102 and D103). After
being filtered out the useless out-of-band signals, the signals are amplified by LNA consisting of Q203
and external components.
Signals from LNA are filtered again by BPF which consists of C228 C226 C238 C229 C227 C239 C947
C259 C948 L214 L204 L203 D905 D203 and D206 before entering the 1st mixer (Q202).
The PWM wave is output by MCU composed of 58 foot and then commutated to adjustable voltage after
filtering to change the capacity of varactor diode D905 D203 D206 D201 D202 and D204 to control the
center frequency of BPF.
st
1 mixer
st
The first IF (49.95MHz) signal is produced after mixing of the receiving signal from LNA and the 1 local
oscillation signal from frequency synthesizer. The first IF signal is filtered out adjacent channel and other
useless signals by crystal filter (XF201).
IF Circuit
st
The 1 IF signal from crystal filter is amplified by the first IF amplifier (Q201) before processing of IC in
IF( IC200，NJM2591V or TA31136FN).
nd nd
IF IC consists of the 2 mixer, 2 local oscillation, IF amplifier, limiter, frequency discriminator and noise
amplifier.
rd
Frequency (16.8MHz) produced by TCXO(X1) is amplified and then selects 3 harmonics (51.4MHZ) as
the second local oscillator signal source. The second IF signals (450kHz) are generated after signals
mixing of the second local oscillation (51.4MHz) and the first IF (49.95MHz) in IC200. Audio signals are
demodulated and outputted by IC200 after the second IF signals are amplified and limited in IC200 and
then filtered by ceramic filter(450kHz).
23