Yaesu FT-7100M, Technical Supplement

Page: 7 / 68

7
Circuit Description
While no carrier is received, pin 75 of Q1075 remains
"high," turning on the squelch switch Q1079 ( RT1N241M )
to disable audio output from the speaker.
Transmit Signal Path
The speech signal from the microphone passes through
the MIC jack J2002 to AF amplifier Q2011 ( M5223AGP )
on the PANEL UNT. The amplified speech signal is sub-
jected to amplitude limiting by
Q2011 ( M5223AGP ), then
passes through the panel interface jacks J2001 and J1002
to MAIN Unit. On the MAIN UNIT, the speech signal
passes through buffer amplifier
Q1045 ( NJM2902V-1/-2 )
and a low-pass filter network at Q1045 ( NJM2902V-3 ) to
deviation control VR1001 (for UHF Tx audio) or VR1002
(for VHF Tx audio).
VHF Transmit Signal Path
The adjusted speech signal from VR1002 is delivered
to VHF VCO Q1025 , which frequency modulates the
transmitting VCO D1025 ( HVC200A ).
The modulated transmit signal passes through buffer
amplifier Q1021 ( 2SC5374 ), a low-pass filter network, and
another buffer amplifier Q1110 ( 2SC5374 ) to another low-
pass filter network.
The filtered transmit signal is applied to the Pre-Drive
amplifier Q1111 ( 2SK3074 ) and Drive amplifier Q1112
( 2SK2975 ), then finally is amplified by Power amplifier
Q1113 ( 2SK3478 ) up to 50 Watts. This three stage power
amplifier’s gain is controlled by the APC circuit.
The 50-Watt RF signal passes through a low-pass filter
network, antenna switch D1060 ( UM9957F ), and another
low-pass filter network, and then is delivered to the ANT
jack.
UHF Transmit Signal Path
The adjusted speech signal from VR1001 is delivered
to UHF VCO Q1024 which frequency modulates the trans-
mitting VCO D1022 ( HVC200A ).
The modulated transmit signal passes through buffer
amplifiers Q1020 and Q1110 (both 2SC5374 ) to a high-
pass filter network.
The filtered transmit signal is applied to the Pre-Drive
amplifier Q1111 ( 2SK3074 ) and Drive amplifier Q1112
( 2SK2975 ), then finally is amplified by Power amplifier
Q1113 ( 2SK3478 ) up to 35 Watts. This three stage power
amplifier’s gain is controlled by the APC circuit.
The 35-Watt RF signal passes through a high-pass fil-
ter network, antenna switch D1053 and D1054
( UM9957F ), low-pass filter and high-pass filter networks,
and then is delivered to the ANT jack.
VHF Tx APC Circuit
A portion of the power amplifier output is rectified by
D 1 0 6 3 ( 1 S S 3 2 1 ), D 1 0 6 5 ( 1 S S 3 1 9 ) and Q 1 1 1 6
( 2SC4154E ), then delivered to APC Q1045 ( NJM2902V )
as a DC voltage which is proportional to the output level
of the power amplifier.
The APC Q1045 compares the rectified DC voltage
from the power amplifier and the reference voltage from
the main CPU
Q1075 , producing a control voltage for the
Automatic Power Controller Q1114 ( RT1P441U ) and
Q1115 ( RT1N241M ) which regulates supply voltage to
the Pre-Drive amplifier Q1111 , Drive amplifier Q1112 ,
and Power amplifier Q1113 , so as to maintain stable out-
put power under varying antenna loading conditions.
UHF Tx APC Circuit
A portion of the power amplifier output is rectified by
D 1 0 6 4 ( 1 S S 3 1 9 ), D 1 0 6 5 ( 1 S S 3 1 9 ) and Q 1 1 1 6
( 2SC4154E ), then delivered to APC Q1045 ( NJM2902V )
as a DC voltage which is proportional to the output level
of the power amplifier.
The APC Q1045 compares the rectified DC voltage
from the power amplifier and the reference voltage from
the main CPU
Q1075 , producing a control voltage for the
Automatic Power Controller Q1114 ( RT1P441U ) and
Q1115 ( RT1N241M ) which regulates supply voltage to
the Pre-Drive amplifier Q1111 , Drive amplifier Q1112 ,
and Power amplifier Q1113 , so as to maintain stable out-
put power under varying antenna loading conditions.
VHF PTT Circuit
When the PTT switch is pressed, pin 46 of sub CPU
Q2007 ( M38039FFFP ) goes “1V,” which sends the “PTT”
command to the main CPU, Q1075 . When it receives the
“PTT” command, pin85 of Q1075 goes “high” to control
local switch D1050 ( DAN235E ), filter switch D1051 ,
D1052 , TX switch D1062 ( MC2848 ), and APC switch
Q1114 / Q1115 , which activates the VHF Tx circuit. Mean-
while, pin 86 of Q1075 goes “low,” which disables the
VHF Rx circuit.