Yaesu VX-7R, Service Manual

9

Circuit Description

(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 modu-
lator 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 oscil-

lates at the desired VHF transmitting frequency. The
modulated VCO signal is buffered by amplifier Q4006
(

EC3H07B

) and Q1017 and delivered 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 modulated 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 mod-
ulator 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 transmitting frequency. The
modulated VCO signal is buffered 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 mod-

ulated UHF 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 D1048. RF out-
put is passed through the T/R switch and low-pass filter
to suppress harmonics and spurious products before out-
put 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 transmitting fre-
quency. The modulated VCO signal is buffered by ampli-
fier 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 prod-
ucts before output gets to the antenna at the antenna ter-

minal.