Table of Contents
Advertisement
1. Receive Signal Path
Incoming RF from the antenna jack is delivered to the
Main Unit and passes through a low-pass filter consist-
ing of coils L1001, L1002, & L1003 and capacitors C1001,
C1004, C1011, C1013, & C1018 to the antenna switch-
ing diodes D1004 & D1005 (both RLS135), and enter a
high-pass filter consisting of coils L1011 & L1013 and
capacitors C1056, C1059, C1062, C1067, & C1074.
Signals within the frequency range of the transceiver are
amplified by Q1018 (3SK294) and enter a band-pass fil-
ter consisting of coils L1019, L1020, & L1021 and capac-
itors C1110, C1114, C1290, C1116, C1117, C1291, C1119,
C1120, & C1122 to remove unwanted signals, before first
mixing by Q1025 (3SK318).
Buffered output from the VCO is amplified by Q1008
(2SC5008) to provide a pure first local signal between
203.300 and 210.525 MHz for injection to the first mixer
Q1025 (3SK318).
The 47.25 MHz first mixer product then passes through
monolithic crystal filter XF1001 (7050M 47.25S13A) to
strip away all but the desired signal, which is then am-
plified by Q1028 (2SC4915). The amplified first IF sig-
nal is applied to FM IF subsystem IC Q1031 (NJM2591V),
which contains the second mixer, second local oscilla-
tor, limited amplifier, noise amplifier, and RSSI amplifi-
er.
A second local signal is produced from the PLL refer-
ence/second local oscillator of X1001 (11.7 MHz). The
11.7 MHz reference signal is quadrupled by Q1029
(2SC4915), then delivered to mixer section of Q1031
(NJM2591V) which produce the 450 kHz second IF mixed
with the first IF signal.
The second IF then passes through the ceramic filter
CF1001 (LTWC450F) to strip away unwanted mixer
products, and is then applied to the limited amplifier in
Q1031 (NJM2591V), which removes amplitude varia-
tions in the 450 kHz IF, before detection of the speech by
the ceramic discriminator CD1001 (JTM450CX24).
2. Audio Amplifier
The demodulated audio signal from the Q1031
(NJM2591V) passes through a de-emphasis network, a
high-pass filter Q1046 (2SC4617-R), and a low-pass fil-
ter Q1041 (2SC4617-R). Then passes through the audio
volume control section of the D/A IC Q1030 (BU2502FS)
and audio mute switch Q1034 (CD4066BPW) to the au-
dio power amplifier Q1047 (TDA2822L), providing up to
700 mW of audio power to the 16-ohm loudspeaker.
Circuit Description
3. Squelch Control
When no carrier received, noise at the output of the de-
tector stage in Q1031 (NJM2591V) passes through a
band-pass filter consisting of resistors R1160 & R1165
and capacitors C1208 & C1211 to the buffer amplifier
Q1033 (2SC4617-R), then rectified by D1026 and D1027
(both DA221).
The resulting DC squelch control voltage is passed to pin
78 of the microprocessor Q1032 (µPD78F1167GC). If no
carrier is received, this signal causes pin 99 of Q1032
(µPD78F1167GC) to go "low" and activates the audio mute
switch Q1034 (CD4066BPW). Thus, the microprocessor
blocks output from the audio amplifier, and silences the
receiver, while no signal is being received (and during
transmission, as well).
When a carrier appears at the discriminator, noise is re-
moved from the output, causing pin 78 of the micropro-
cessor Q1032 (µPD78F1167GC) to go "low", this signal
causes pin 99 of Q1032 (µPD78F1167GC) to go "high"
and diables the audio mute switch Q1034 (CD4066BPW),
thus allowing audio to pass through the audio amplifier
Q1047 (TDA2822L) to the loudspeaker.
4. Transmit Signal Path
The speech input from the microphone MC1001 passes
t h r o u g h t h e m i c r o p h o n e s e l e c t s w i t c h Q1034
(CD4066BPW) to the audio amplifier section of Q1003
(LM2902PW) which adjusts the microphone gain. The
speech signal passes through the IDC section and low-
pass filter of Q1003 (LM2902PW).
The filtered audio signal is applied to Q1030 (BU2502FS)
which adjusts the modulation to the optimum level, then
is applied to varactor diode D1011 (HVC306B) which fre-
quency modulates the VCO Q1010 (2SC5231).
The modulated signal from the VCO Q1010 (2SC5231)
is buffered by Q1008 (2SC5006). The low-level transmit
signal is then passes through the TX switching diode
D1023 (DAN235E) to the driver amplifier Q1020
(2SC5226), exciter amplifier Q1015 (RD01MUS1), then
amplified transmit signal is applied to the final amplifi-
er Q1009 (RD09MUS2) up to 6.0 watts output power.
The transmit signal passes through the antenna switch
D1004 (RLS135) and is low-pass filtered to suppress har-
monic spurious radiation before delivery to the anten-
na.
7
Advertisement
Table of Contents
