Standard Horizon HX851, Руководство по обслуживанию

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7
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.
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 Q 1 0 3 4
( 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.
Circuit Description