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1. Receive Signal Path
Incoming RF from the antenna jack is delivered to the RF
Unit and passes through a low-pass filter consisting of
coils L1025, L1026, and L1027, capacitors C1229, C1235,
C1237, C1241, C1243, C1245 and C1246, and antenna
switching diode D1033 (RLS135).
Signals within the frequency range of the transceiver en-
ter a Varactor-tuned band-pass filter consisting of coils
L1019 and L1022, capacitors C1217, C1218 and C1250, and
varactor diode D1030 (1SV323), then amplified by Q1044
(2SC5006) and enter a Varactor-tuned band-pass filter
consisting of coils L1016, L1017 and L1018, capacitors
C1182, C1184, C1185, C1186, C1187, C1188, C1191, C1192,
C1195, C1197, and C1199, and varactor diodes D1026,
D1027, and D1028 (all HVC350B), before first mixing by
Q1041 (3SK320).
Buffered output from the VCO is amplified by Q1023
(2SC5374) to provide a pure first local signal between
134.35 and 141.575 MHz for injection to the first mixer
Q1041 (3SK320).
The 21.7 MHz first mixer product then passes through
monolithic crystal filter XF1001/XF1002 to strip away all
but the desired signal, which is then amplified by Q1037
(2SC4400). The amplified first IF signal is applied to FM
IF subsystem IC Q1033 (NJM2591V), which contains the
second mixer, second local oscillator, limited amplifier,
noise amplifier, and RSSI amplifier.
A second local signal is produced from the PLL reference/
second local oscillator of X1001 (21.25 MHz). The 21.25
MHz reference signal is delivered to mixer section of
Q1033 (NJM2591V) which produce the 450 kHz second
IF mixed with the first IF signal.
The second IF then passes through the ceramic filter
CF1001 to strip away unwanted mixer products, and is
then applied to the limited amplifier in Q1033
(NJM2591V), which removes amplitude variations in the
450kHz IF, before detection of the speech by the ceramic
discriminator CD1001.
2. Audio Amplifier
The demodulated audio signal from the Q1033
(NJM2591V) passes through a band-pass filter and high-
pass filter, then applied to the de-emphasis. Then passes
through the audio volume and the audio power amplifier
Q1009 (TDA2822D), providing up to 600 mW of audio
power to the 4 ohm loudspeaker.
Circuit Description
3. Squelch Control
The squelch circuitry consists of a noise amplifier and
band-pass filter and noise detector within Q1033
(NJM2591V).
When no carrier received, noise at the output of the de-
tector stage in Q1033 (NJM2591V) is amplified and band-
pass filtered by the noise amplifier section of Q1033
(NJM2591V) and the network between pins 7 and 8, and
then rectified by detection circuit in Q1033 (NJM2591V).
The resulting DC squelch control voltage is passed to pin
73 of the microprocessor Q1043 (HD64F38024W). If no
carrier is received, this signal causes pin 67 of Q1043
(HD64F38024W) to go low and pin 66 to go high. Pin 66
signals of Q1043 (HD64F38024W) to disable the supply
voltage to the audio amplifier Q1009 (TDA2822D), mean-
while pin 18 hold the green (Busy) half of the LED D1020
(CL-165HR/YG-D) off.
Thus, the microprocessor blocks output from the audio
amplifier, and silences the receiver, while no signal is be-
ing received (and during transmission, as well).
When a carrier appears at the discriminator, noise is re-
moved from the output, causing pin 73 of Q1043
(HD64F38024W) to go low and pin 18 to go high. Pin 66
signals of Q1043 (HD64F38024W) to activate the green
(Busy) half of the LED D1020 (CL-165HR/YG-D) via Q1029
(2SC4617).
The microprocessor Q1043 (HD64F38024W) then checks
for CTCSS or CDCSS code squelch information, if enabled.
If not transmitting and CTCSS or CDCSS is not activated,
or if the received tone or code matches that programmed,
allows audio to pass through the audio amplifier Q1009
(TDA2822D) to the loudspeaker by enabling the supply
voltage to it via Q1014 (FMTL718TA).
4. Transmit Signal Path
The speech input from the microphone MC1001 passes
through the audio amplifier Q1051 (LM2902PW), which
is adjusted the microphone gain. The speech signal pass-
es through pre-emphasis circuit to Q1051 (LM2902PW),
which contains the IDC, and low-pass filter.
The filtered audio signal is applied to Q1030 (M62364FP)
which is adjusted the audio level, then is applied to var-
actor diode D1007 (HVC350B), which frequency modu-
lates the VCO Q1012 (2SC5231). A portion of the audio
signal from Q1030 (M62364FP) is applied to X1001 (21.25
MHz).
The processed audio may then be mixed with a CTCSS
tone generated by microprocessor Q1043 (HD64F38024W)
for frequency modulation of the PLL carrier (up to ±5 kHz
from the unmodulated carrier) at the transmitting frequen-
cy.
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