Circuit Description - Vertex Standard VX-230 Series Service Manual

Circuit Description

1. Circuit Configuration by Frequency
The receiver is a Double-conversion Super-heterodyne with a
first intermediate frequency (IF) of 67.65 MHz and a second IF
of 450 kHz. Incoming signal from the antenna is mixed with
the local signal from the VCO/PLL to produce the first IF of
67.65 MHz. This is then mixed with the 67.2 MHz second local
oscillator output to produce the 450 kHz second IF. This is de-
tected to give the demodulated signal.
The transmit signal frequency is generated by the PLL VCO,
and modulated by the signal from the microphone. It is then
amplified and sent to the antenna
2. Receiver System
2-1. Front-end RF amplifier
Incoming RF signal from the antenna is delivered to the RF
Unit and passes through Low-pass filer, antenna switching di-
ode, high pass filter and removed undesired frequencies by var-
actor diode (tuned band-pass filer).
The passed signal is amplified in Q1013 (MSG33001) and
moreover cuts an image frequency with the tuned band pass
filter and comes into the 1st mixer.
2-2. First Mixer
The 1st mixer consists of the Q1024 (3SK293). Buffered out-
put from the VCO is amplified by Q1027 (2SC5005) to pro-
vide a pure first local signal between 382.35 and 444.35 MHz
(Type "D", VTX), 382.35 and 452.35 MHz (Type "D", EXP),
or 332.35 and 402.35 MHz (Type "A") for injection to the first
mixer.
The IF signal then passes through monolithic crystal filters
XF1001 (±7.5 kHz BW) to strip away all but the desired signal.
2-3. IF Amplifier
The first IF signal is amplified by Q1033 (2SC5226).
The amplified first IF signal is applied to FM IF subsystem IC
Q1038 (NJM2591V) which contains the second mixer, sec-
ond local oscillator, limiter amplifier, noise amplifier, and RSSI
amplifier.
The signal from reference oscillator X1002 becomes 4 times of
frequencies in Q1038, it is mixed with the IF signal and be-
comes 450 kHz.
The second IF then passes through the ceramic filter CF1001
(LTM450FW) to strip away unwanted mixer products, and is
applied to the limiter amplifier in Q1038, which removes ampli-
tude variations in the 450 kHz IF, before detection of the speech
by the ceramic discriminator CD1001 (JTBM450CX24).
2-4. Audio amplifier
Detected signal from Q1038 is inputted to TX/RX switch
Q1001-4 (TC74VHC4066AFT).
The signal which appeared from Q1001 is in high pass filter
Q1050 (NJM12902V).
The signal which passed Q1050 goes to AF volume (VR1001).
And then the signal goes to audio amplifier Q1005
(NJM2070M).
The output signal from Q1005 is in audio speaker.
VX-230 Series UHF FM Transceiver Service Manual
2-5. Squelch Circuit
There are 16 levels of squelch setting from 0 to 15. The level 0
means open the squelch. The level 1 means the threshold set-
ting level and level 14 means tight squelch. From 2 to 13 is
established in the middle of threshold and tight.
The bigger figure is nearer the tight setting. The level 15 be-
comes setting of carrier squelch.
2-5-1. Noise Squelch
Noise squelch circuit is composed of the band path filter of
Q1038, and noise detector D1029 (1SS400G).
When a carrier isn't received, the noise ingredient which goes
out of the demodulator Q1038 is amplified in Q1038 through
the band path filter Q1038, is detected to DC voltage with D1029
and is inputted to 52pin (the A/D port) of the Q1026 (CPU).
When a carrier is received, the DC voltage becomes low be-
cause the noise is compressed.
When the detected voltage to CPU is high, the CPU stops AF
output with Q1001-3 "OFF" by making the 41pin (CPU) "L"
level.
When the detection voltage is low, the CPU makes Q1001 ON
with making 41pin "H" and the AF signal is output.
2-5-2. Carrier Squelch
The CPU (53pin: A/D port) detect RSSI voltage output from
Q1038 12 pin, and controls AF output.
The RSSI output voltage changes according to the signal strength
of carrier. The stronger signal makes the RSSI voltage to be
higher voltage.
The process of the AF signal control is same as Noise Squelch
The shipping data is adjusted –1dBμ (EMF) higher than squelch
tight sensitivity.
3. Transmitter System
3-1. Mic Amplifier
The AF signal from internal microphone MC1001 or external
microphone J1002 is amplified with microphone amplifier
Q1049-3 (NJM12902V).
This signal enters high pass filter Q1050 via the mute switch
Q1001-1 (TC74VHC4066AFT).
Afterwards, the switch circuit is controlled in the gain by way
of microphone gain volume Q1012 (M62364FP-CH1).
AF signal is passes a pre-emphasis circuit and is input to the
limiter amplifier Q1049-2 (NJM12902V).
The signal passed splatter filter of Q1049 and adder amplifier
Q1046 is adjusted by maximum deviation adjustment volume
Q1012 (M62364FP-CH4).
The AF signal ingredient is amplified Q1046 (NJM12902V).
After that, it is made FM modulation to transmit carrier by the
modulator D1014 (HVC383B) of VCO.
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