Yaesu VX-7R - TECHNICAL Service Manual page 9

it switches Q1048 (KRC654U) to disable the receiver cir-
cuits. This causes the "red" mode of BUSY/TX lamp D3033
to light.
(2) Modulation
Voice signal input from either built-in microphone
MC3001 (EM-140) on the CNTL-UNIT or external jack
J2002 on the AF-UNIT is pre-emphasized by C3012 and
R3031, and processed by microphone amplifier Q3018
(NJM3403AV), IDC (instantaneous deviation control) cir-
cuit Q1014 to prevent overmodulation, and fed through
active low-pass filter Q1014.
During CTCSS operation, the voice signal is mixed with
the TONE ENC subaudible tone signal from pin 43 of
the CPU and delivered to the RF-UNIT through jacks
J3003 and J1008. During DTMF operation, the DTMF
tones from pin 44 of the CPU are fed to the IDC stage.
(3) 145-MHz-Band Transmission
Modulating audio from the CNTL-UNIT passes
through deviation setting D/A converter Q3012 to the
VHF modulator portion of the VCO-UNIT mounted on
the RF-UNIT. This signal is applied to varactor D4005
(HSC277) in the tank circuit of VHF VCO Q4004
(EC3H07B), which oscillates at the desired VHF trans-
mitting frequency. The modulated VCO signal is buff-
ered by amplifier Q4006 (EC3H07B) and Q1017 and de-
livered through VHF T/R diode switch D1041 to the RF-
UNIT. The modulated low-level VHF transmit signal
from the VCO is passed through diode switch D1043
(DAN222) to amplifier Q1014 (2SC5226-5). The modu-
lated VHF transmit signal from the VCO is amplified by
Q1023 (2SK3475) and RF power amplifier Q1027
(2SK3476) up to 0.05, 1.0, 2.5 or 5 Watts (depending on
the power source). The RF output passes through TX
diode switch D1053. RF output is passed by the T/R
switch and low-pass filter to suppress harmonics and
spurious products before output gets to the antenna at
the antenna terminal.
(4) 435-MHz-Band Transmission
Modulating audio from the CNTL-UNIT passes
through deviation setting D/A converter Q3012 to the
UHF modulator portion of the VCO-UNIT mounted on
the RF-UNIT. This signal is applied to varactor D4002
(HSC277) in the tank circuit of UHF VCO Q4002
(EC3H07B), which oscillates at the desired UHF trans-
mitting frequency. The modulated VCO signal is buff-
Circuit Description
ered by amplifier Q4006 and Q1016 and delivered
through UHF T/R diode switch D1045 to the RF-UNIT.
The modulated low-level UHF transmit signal from the
VCO is passed through diode switch D1045 (HN2D01FU)
to amplifier Q1014. The modulated UHF transmit signal
from the VCO is amplified by Q1023 and RF power am-
plifier Q1027 up to 0.05, 1.0, 2.5 or 5 Watts (depending
on the power source). The RF output passes through TX
diode switch D1048. RF output is passed through the T/
R switch and low-pass filter to suppress harmonics and
spurious products before output gets to the antenna at
the antenna terminal.
(5) 50-MHz-Band Transmission
Modulating audio from the CNTL-UNIT passes
through deviation setting D/A converter Q3012 to the 50
MHz modulator portion of the VCO-UNIT mounted on
the RF-UNIT. This signal is applied to varactor D4009
(HSC277) in the tank circuit of 50 MHz VCO Q4005
(EC3H07B), which oscillates at the desired 50 MHz trans-
mitting frequency. The modulated VCO signal is buff-
ered by amplifier Q4006 and Q1018 and delivered
through 50 MHz T/R diode switch D1046 to the RF-UNIT.
The modulated low-level 50 MHz transmit signal from
the VCO is passed through diode switch D1046
(HN2D01FU) to amplifier Q1014. The modulated 50 MHz
transmit signal from the VCO is amplified by Q1023 and
RF power amplifier Q1027 up to 0.05, 1.0, 2.5 or 5 Watts
(depending on the power source). The RF output passes
through TX diode switch D1058. RF output is passed
through the T/R switch and low-pass filter to suppress
harmonics and spurious products before output gets to
the antenna at the antenna terminal.
9