Vertex Standard VX-4200 Series Service Manual page 10

Circuit Description
the control from the CPU, it passes in the compandor circuit
inside of Q1021 (LA8630M) and it is output and it passes a
pre-emphasis circuit. Q1063 (BU4066BCFV) becomes "OFF"
when an option unit is attached and the AF signal from Q1037
(AK2345) goes via the option unit. When an option unit isn't
attached, Q1063 (BU4066BCFV) becomes "ON," the signal
passes Q1063 (BU4066BCFV) and is input to Q1037
(AK2345). The signal passed limiter and splatter filer of Q1037
(AK2345) is adjusted by maximum deviation adjustment vol-
ume Q1029 (M62364FP). The adjusted low frequency signal
ingredient is amplified by Q1074 (NJM12902V), added modu-
lation terminal of TCXO (X1003), the FM modulation is made
by reference oscillator. The high frequency signal ingredient is
amplified Q1074 (NJM12902V), and adjusted the level by
volume Q1029 (M62364FP) to make frequency balance be-
tween low frequency. After that, it is made FM modulation to
transmit carrier by the modulator D1030 (HVC383B) of VCO.
3-2. Drive and Final amplifier
The modulated signal from the VCO Q1054 (2SK508) is buff-
ered by Q1049 (2SC5226) and amplified by Q1038 and Q1002
(both 2SC5226). The low-level transmit signal is then applied
to the Power Module Q1028 (S-AV32) for final amplification
up to 50 watts output power. The transmit signal then passes
through the antenna switch D1006 (UM9957F) and is low-pass
filtered to suppress away harmonic spurious radiation before
delivery to the antenna.
3-3. Automatic Transmit Power Control
The output power of Power Module is detected by CM coupler,
it is detected by D1013 and D1014 (both HSM88AS) and is
input to comparator Q1090 (NJM12902V). The comparetor
compares two different voltages and makes output power stable
by controlling the bias voltage of Power Module. There are 3
levels of output power (Hi, Mid and Lo), it is switched by the
voltage of Q1029-1 (M62364FP).
3-4. PLL Frequency Synthesizer
The frequency synthesizer consists of PLL IC Q1085
(SK7025DK), Q1045 (DTC114TE), VCO, TCXO (X1003)
and buffer amplifier. The output frequency from TCXO is 16.8
MHz and the tolerance is ±2.5 ppm (in the temperature range -
30 to +60 degrees).
E-2
3-4-1. VCO
While the radio is receiving, the RX oscillator Q1054 (2SK508)
in VCO generates a programmed frequency between 184.85
and 224.85 MHz as 1st local signal. While the radio is transmit-
ting, the TX oscillator Q1058 (2SC3356) in VCO generates a
frequency between 134 and 174 MHz. The output from oscilla-
tor is amplified by buffer amplifier Q1049 (2SC5226) and be-
comes output of VCO. The output from VCO is divided, one is
amplified by Q1057 (2SC5226) and feed back to pin 5 of the
PLL IC Q1085 (SK7025DK). The other is amplified in Q1038
(2SC5226) and in case of the reception, it is put into the mixer
as the 1st local signal through D1022 (DA221), in transmis-
sion, it is amplified in Q1038 (2SC5226), and more amplified
in Q1002 (2SC5226) through D1022 (DA221) and it is put
the input terminal of the Power Module Q1028 (S-AV32).
3-4-2. VCV CNTL
Tuning voltage (VCV) of VCO is expanding the lock range of
VCO by controlling the anode of varactor diode at the negative
voltage and the control voltage from PLL IC Q1085
(SK7025DK). The negative voltage is added to the varactor
diode after converted to negative by Q1035 (SPM5001), which
is output voltage of D/A converter Q1029 (M62364FP).
3-4-3. PLL
The PLL IC Q1085 (SK7025DK) consists of reference divider,
main divider, phase detector, charge pumps and fractional ac-
cumulator. The reference frequency from TCXO is inputted to
pin 8 of PLL IC Q1085 (SK7025DK) and is divided by refer-
ence divider. This IC is decimal point dividing PLL IC Q1085
(SK7025DK) and the dividing ratio becomes 1/8 of usual PLL
frequency step. Therefore, the output of reference divider is 8
times of frequencies of the channel step. For example, when
the channel stepping is 5 kHz, the output of reference divider
becomes 40 kHz. The other hand, inputted feed back signal to
pin 5 of PLL IC Q1085 (SK7025DK) from VCO is divided
with the dividing ratio which becomes same frequency as the
output of reference divider. These two signals are compared by
phase detector, the phase difference pulse is generated. The phase
difference pulse and the pulse from fractional accumulator pass
through the charge pumps and LPF. It becomes the DC voltage
(VCV) to control the VCO. The oscillation frequency of VCO
is locked by the control of this DC voltage. The PLL serial data
from CPU Q1083 (LC87F74C8A) is sent with three lines of
SDO (pin 2), SCK (pin 1) and PSTB (pin 3). The lock condi-
tion of PLL is output from the UL (pin 18) terminal and UL
becomes "H" at the time of the lock condition and becomes "L"
at the time of the unlocked condition. The CPU Q1083
(LC87F74C8A) always watches over the UL condition, and
when it becomes "L" unlocked condition, the CPU Q1083
(LC87F74C8A) prohibits transmitting and receiving.