Circuit Description; Circuit Configuration By Frequency; Receiver System; Transmitter System - Vertex Standard VX-350 Series Service Manual

1. Circuit Configuration by Frequency

The receiver is a Double-conversion Super-heterodyne with a
first intermediate frequency (IF) of 50.85 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
50.85 MHz. This is then mixed with the 50.4 MHz second local
oscillator output to produce the 450 kHz second IF. This is de-
tected to give the demodulated signal. The transmit signal fre-
quency 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 D1003 (RLS135), high pass filter and removed undesired
frequencies by varactor diodes D1007 and 1009 (both 1SV331)
(tuned band-pass filer). The passed signal is amplified in Q1021
(MSG33001) and moreover cuts an image frequency with the
tuned band pass filter D1016 and 1018 (both 1SV331) and
comes into the 1st mixer.
2-2. First Mixer
The 1st mixer consists of the Q1036 (3SK293). Buffered out-
put from the VCO is amplified by Q1031 (2SC5005) to pro-
vide a pure first local signal between 399.15 and 461.15 MHz
for injection to the first mixer. The IF signal then passes through
monolithic crystal filters XF1001 (±5.5 kHz BW) to strip away
all but the desired signal.
2-3. IF Amplifier
The first IF signal is amplified by Q1048 (2SC5226). The am-
plified first IF signal is applied to FM IF subsystem IC Q1053
(NJM2591) which contains the second mixer, second local os-
cillator, limiter amplifier, noise amplifier, and S-meter amplifi-
er. The signal from reference oscillator X1002 becomes 3 times
of frequencies in Q1053, it is mixed with the IF signal and be-
comes 450 kHz. The second IF then passes through the ceramic
filter CF1001 (LTM450EW: wide channels), CF1002
(LTM450GW: narrow channels) to strip away unwanted mixer
products, and is applied to the limiter amplifier in Q1053, which
removes amplitude variations in the 450kHz IF, before detec-
tion of the speech by the ceramic discriminator CD1001
(ECDA450C24).
2-4. Audio amplifier
Detected signal from Q1053 is inputted to mute switch Q1001-
3 (SN74LV4066APWR) and option switch Q1001-2. The sig-
nal which appeared from Q1001-2 is in band pass filter Q1066
(NJM12902V). In the case an optional unit is installed, the
Q1001-2 is made "OFF" and the AF signal from Q1001-3 goes
the optional unit. In the case an optional unit is not installed,
Q1001-2 is made "ON" and the signal goes through Q1001-2.

Circuit Description

The signal which passed Q1066 goes to AF volume (VR1001).
And then the signal goes to audio amplifier Q1007
(NJM2070M). The output signal from Q1007 is in audio speak-
er.
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 thresh-
old setting 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
Q1053, noise amplifier Q1058 (2SC4617), and noise detector
D1042 and D1043 (both DA221). When a carrier isn't received,
the noise ingredient which goes out of the demodulator Q1053
is amplified in Q1058 through the band path filter Q1053, is
detected to DC voltage with D1042 and D1043 and is inputted
to 48 pin (the A/D port) of the Q1044 (CPU: LC87F5864B).
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 Q1001-1 "OFF"
by making the 39 pin (CPU) "L" level. When the detection volt-
age is low, the CPU makes Q1001-1 "ON" with making 39 pin
"H" and the AF signal is output.
2-5-2. Carrier Squelch
The CPU (47 pin: A/D port) detect RSSI voltage output from
Q1053 12 pin, and controls AF output. The RSSI output volt-
age changes according to the signal strength of carrier. The stron-
ger 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 3dB higher than squelch tight sensi-
tivity.

3. Transmitter System

3-1. Mic Amplifier
The AF signal from internal microphone MC1001 or external
microphone J1002 is amplified with microphone amplifier
Q1069-2 (NJM12904), after passes microphone gain volume
Q1017-CH1 (M62364FP). AF signal is passes a pre-empha-
sis circuit. Q1001-1 (SN74LV4066APW) becomes "OFF"
when an option unit is attached and the AF signal from Q1068
goes via the option unit. When an option unit isn't attached,
Q1001-1 becomes "ON", the signal passes Q1001-1 and is in-
put to the limiter amplifier Q1068-2 (BA2902). The signal
passed splatter filter of Q1068 and adder amplifier Q1065 is
adjusted by maximum deviation adjustment volume Q1017-
CH4 (M62364FP). The AF signal ingredient is amplified
Q1065 (BA2902). After that, it is made FM modulation to trans-
mit carrier by the modulator D1023 (HVC383) of VCO.
7