Yaesu FT-7100M, Technical Supplement

Page: 8 / 68

8
UHF 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, pin81 of Q1075 goes “high” to controls
local switch D1050 , filter switch D1051 , D1052 , TX switch
D1062 and APC switch Q1114 / Q1115 , which activates the
UHF Tx circuit. Meanwhile, pin 82 of Q1075 goes “low,”
which disables the UHF Rx circuit.
VHF PLL
A portion of the output from the VHF VCO Q1025
( 2SC5006 ) passes through buffer amplifiers Q1021
( 2SC5374 ) and Q1040 ( 2SC3120 ) to the programmable
divider section of the PLL IC Q1055 ( M64076AGP ), which
divides the frequency according to the frequency divid-
ing data from the main CPU,
Q1075 . It is then sent to the
phase comparator.
The 21.25 MHz frequency of the reference oscillator
circuit, made up of X1002 and Q1060 ( 2SC5374 ), is di-
vided by the reference frequency divider section of Q1055
into 4250 or 3400 parts to become 5 kHz or 6.25 kHz com-
parative reference frequencies, which are utilized by the
phase comparator.
The phase comparator section of Q1055 compares the
phase between the frequency-divided oscillation frequen-
cy of the VCO circuit and comparative frequency, and its
output is a pulse corresponding to the phase difference.
This pulse is integrated by the charge pump and loop fil-
ter of
Q1055 into a control voltage (VCV) to control the
oscillation frequency of the VHF VCO Q1025 .
Circuit Description
UHF PLL
A portion of the output from the UHF VCO Q1024
( 2SC5006 ) passes through buffer amplifier Q1020
( 2SC5374 ) and Q1038 ( 2SC3120 ) to the programmable
divider section of the PLL IC Q1055 ( M64076AGP ), which
divides the frequency according to the frequency divid-
ing data from the main CPU
Q1075 . It is then sent to the
phase comparator.
The 21.25 MHz frequency of the reference oscillator
circuit, made up of X1002 and Q1060 ( 2SC5374 ), is di-
vided by the reference frequency divider section of Q1055
into 4250 or 3400 parts to become 5 kHz or 6.25 kHz com-
parative reference frequencies, which are utilized by the
phase comparator.
The phase comparator section of Q1055 compares the
phase between the frequency-divided oscillation frequen-
cy of the VCO circuit and comparative frequency, and its
output is a pulse corresponding to the phase difference.
This pulse is integrated by the charge pump and loop fil-
ter of
Q1055 into a control voltage (VCV) to control the
oscillation frequency of the UHF VCO Q1024 .
V/V, U/U Local Oscillator
When the V/V or U/U feature is activated, a portion of
the 21.25 MHz reference is amplified and multiplied by
twelve by
Q1026 ( 2SC3120 ), then passes through band-
pass filter network to buffer amplifier Q1031 ( 2SC3120 ),
which provides the first local signal for V/V or U/U oper-
ation.
Power-on Circuit
When the POWER switch is turned on, pin 16 of main
CPU Q1075 goes “low.” When pin 16 of Q1075 goes
“low,” pin 61 of Q1075 goes “high” to activate the power
switches Q1001 ( 2SA1301 ) and Q1002 ( RT1N241M ),
which supply the DC power to the radio.