Circuit Description - Vertex Standard VXR-9000EV Service Manual

Receive Signal Path
Incoming RF from the RX antenna jack is delivered to the
MAIN Unit and passes through the protection diode
D1001 (1SS302) and D1002 (RN739F) and a varactor-
tuned band pass filter consisting of coils L1044 and L1048,
capacitors C1400, C1402, C1403, C1407, C1408, C1409 and
C1410, and varactor diodes D1033 and D1034 (both
HVU306).
Signals are then applied to the RF amplifier Q1063
(2SC3356). The amplified RF signal is applied through a
varactor-tuned band pass filter consisting of coils L1050
and L1051, capacitors C1427, C1429, C1430, C1431, C1433,
C1434, C1435 and C1436, and varactor diode D1035 and
D1036 (both HVU306) to the 1st mixer Q1018 (SPM5001)
along with the first local signal from the PLL circuit.
The first local signal is generated between 221.35 and
247.35 MHz by the Dual RX VCO, which consists of FET
Q1048 (Low Band; 2SK520) and Q1053 (High Band;
2SK520) and varactor diodes D1018, D1019, D1020, and
D1021 (Low Band; all 1SV229) and D1027, D1028, D1029,
and D1030 (High Band; all 1SV229), according to the pro-
grammed receiving frequency; the local signal then pass-
es 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/XF1002 (Wide; TM7050A MF73P) or
XF1501/XF1502 (Narrow; TM7050A MF73P) which strip
away unwanted mixer products, and the IF signal is ap-
plied to the first IF amplifiers Q1022 (Wide; 2SC5226) or
Q1502 (Narrow; 2SC5226). The amplified first IF signal
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.
A 2nd local oscillator signal, generated by the 72.895 MHz
crystal X1002, produces the 455 kHz second IF signal when
mixed with the first IF signal within Q1028 (TA31136FN).
The second IF signal passes through ceramic filter CF1001
(CFWM455G) or CF1002 (CFWM455F) which strips away
all but the desired signal, and then passes through the lim-
iter amplifier within Q1028 (TA31136FN) to ceramic dis-
criminator CD1001 (CDB455C7), which removes any am-
plitude variations in the 455 kHz IF signal before detec-
tion of speech. The detected audio passes through the low
pass filter, consisting of R1199 and C1244, which rejects
the 455 kHz IF component.

Circuit Description

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 (M51132FP), which adjusts the audio
sensitivity to compensate for audio level variations, then
passes through audio amplifier Q1020 (NJM2904V), au-
dio switch Q1040 (BU4066BCFV), attenuator consisting
of R1233, and limiter amplifier Q1050 (NJM2904V), to the
electronic volume control Q1056 (M51132FP), where the
maximum deviation is set. The audio signal subsequently
passes through the 3-section active low pass filter consist-
ing 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 Q3020 (FX805LG) is de-emphasized by
R3095 and C3080, providing 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 loud-
speaker.
Sub-Audible Signaling (DECODER)
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 Main CPU Q3014
(HD64F2238BFA13) from pin 4 and 8 of Q3020
(FX805LG) which compares the CTCSS tone with the pro-
grammed tone.
Another portion of the audio signal amplified by Q1020
(NJM2904V) passes through the 3-section active low pass
filter Q3044 (NJM2902V) to separate the DCS codes from
the received audio signal. The low pass filtered signal
passes through the phase detector Q3044 (NJM2902V) to
pin 39 of Main CPU Q3014 (HD64F2238BFA13). When a
D C S c o d e i s r e c e i v e d , t h e M a i n C P U Q 3 0 1 4
(HD64F2238BFA13) 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
(HD64F2238BFA13) goes low, turning off the squelch
switch Q3015 (DTC323TK) and passing the received au-
dio signal to the audio power amplifier Q1057 (TDA2003).
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