Circuit Description - Vertex Standard VXR-9000 Service Manual

R S P
ECEIVE IGNAL ATH
Incoming RF from the RX antenna jack is delivered to the
MAIN Unit and passes through the protection diode
D1001 (1SS302) and a varactor-tuned band pass filter con-
sisting of coils L1003 and L1004, capacitors C1015, C1018,
C1021, C1032, and C1044, and diodes D1003 and D1004
(both HVU350). Signals are then applied to the RF ampli-
fier, Q1009 (2SC3357). The amplified RF signal is applied
through a varactor-tuned band pass filter consisting of
coils L1010 and L1011, capacitors C1079, C1092, C1082,
C1095 and C1075, and diodes D1007 and D1005 (both
HVU350) to the first mixer Q1018 (SPM5001) along with
the first local signal from the PLL circuit.
The first local signal is generated between 376.65 MHz
and 416.65 MHz by the RX VCO, which consists of FET
Q1048 (2SK508) and varactor diodes D1018 and D1019
(both 1SV282) or FET Q1049 (2SK508) and varactor di-
odes D1020 and D1021 (both 1SV282), according to the
programmed receiving frequency; the local signal then
passes through buffer amplifier Q1059 (2SC5226) and first
local amplifier Q1019 (2SC3357) to the first mixer Q1018
(SPM5001).
The 73.35 MHz first IF signal is applied to monolithic crys-
tal filters XF1001 and XF1002 which strip away unwant-
ed mixer products, and the IF signal is applied to the first
IF amplifiers Q1022 (2SC5226). The amplified first IF sig-
nal is then delivered to the FM IF subsystem IC Q1028
(TA31136FN), which contains the second mixer, second
local oscillator, limiter amplifier, noise amplifier, and FM
detector.
The second local oscillator signal, generated by the 72.895
MHz crystal X1002, produces the 455 kHz second IF sig-
nal when mixed with the first IF signal within Q1028
(TA31136FN). The second IF signal passes through ce-
ramic filter CF1001 or CF1002 which strips away all but
the desired signal, and then passes through the limiter
amplifier within Q1028 (TA31136FN) to ceramic discrim-
inator CD1001, which removes any amplitude variations
in the 455 kHz IF signal before detection of speech. The
detected audio passes through the low pass filter, con-
sisting of R1199 and C1244, which rejects the 455 kHz IF
component.
The audio signal from the MAIN Unit is delivered to the
CNTL Unit and passes through the audio amplifier Q1020
(NJM2904V) to the active high pass filter section of Q3020
(FX805LG), which rejects the sub-audible frequency com-
ponent. The filtered audio signal is delivered to electron-
ic volume Q1056, which adjusts the audio sensitivity to
compensate for audio level variations, then passes through
audio amplifier Q1020 (NJM2904V), audio switch Q1040
(BU4066BCFV), attenuator consisting of R1233, and lim-
iter amplifier Q1050 (NJM2904V), to the electronic vol-
VXR-9000 UHF Service Manual

Circuit Description

ume control Q1056 (M51132FP), where the maximum de-
viation is set. The audio signal subsequently passes
through the 3-section active low pass filter consisting of
Q1017-1/-2/-3 (NJM2902V) and audio amplifier Q1001
(NJM2902V) to providing the repeater transmit audio.
A portion of the audio signal from the active high pass
filter section of Q4024 (NJM2902V) is de-emphasized con-
sisting of Q3036 (TA75S01F), R3198, and C3144, provid-
ing a flat audio response. The filtered audio then passes
through the active band pass filter Q3021 (NJM2902V)
and audio mute gate Q3015 (DTC323TK) to audio power
amplifier Q1057 (TDA2003), providing up to 2 Watts of
audio power to the 8 Ohm loudspeaker.
S -A S
UB UDIBLE IGNALING
A portion of the audio signal from the audio amplifier
Q1020 (NJM2904V) passes through the 3-section active
low pass filter Q1025 (NJM2902V) and the low pass fil-
tering section of Q3020 (FX805LG) to separate the CTC-
SS tones from the received audio signal. The CTCSS tones
are sent to the CTCSS decoder section of Q3020
(FX805LG). When a CTCSS tone is received, the CTCSS
information is delivered to pin 77 of the Main CPU Q3014
(HD64F2238) from pin 4 and 8 of Q3020 (FX805LG) which
compares the CTCSS tone with the programmed tone.
Another portion of the audio signal passes through the 3-
section active low pass filter Q3044 (NJM2902V) to sepa-
rate the DCS codes from the received audio signal. The
low pass filtered signal passes through the phase detec-
tor Q3044 (NJM2902V) to pin 39 of the Main CPU Q3014
(HD64F2238). When a DCS code is received, the Main
CPU Q3014 (HD64F2238) compares the DCS code with
the programmed code.
If the received CTCSS tone or DCS code matches the pro-
grammed tone or code, pin 4 of the Main CPU Q3014
(HD64F2238) goes low, turning off the squelch switch
Q3015 (DTC323TK) and passing the received audio sig-
nal to the audio power amplifier Q1057 (TDA2003V).
S C
QUELCH ONTROL
The squelch circuit consists of noise amplifier Q1033
(2SC4116GR) and noise detector D1015 (MA143) on the
MAIN Unit, and control circuitry within Main CPU Q3014
(HD64F2238) on the CNTL Unit.
When no carrier is received, noise at the output of the au-
dio detector stage of Q1028 (TA31136FN) is amplified by
Q1033 (2SC4116GR), and then rectified by D1015 (MA143)
to provide a DC control voltage for the squelch switch.
The resulting DC voltage is delivered to pin 23 of J1005.
The DC voltage from the MAIN Unit is delivered to the
A-D analog input port (pin 51) of the Main CPU Q3014
(HD64F2238) on the CNTL Unit, which compares the
( D )
ECODER
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