8
Circuit Description
passed through a band-pass filter to first mixer Q1013
(
2SC4915-0
). Meanwhile, HF output from the VCO-UNIT
is amplified by Q1018 and applied through diode T/R
switch D1046 to mixer Q1013 as the first local signal.
The 47.25-MHz intermediate frequency product of the
mixer is delivered to the AF-UNIT.
The TUNE voltage from the CPU on the CNTL-UNIT is
amplified by DC amplifier Q3017 and applied to varac-
tors D1013 (
HVR100
) in the variable frequency band-pass
filters. By changing the electrostatic capacitance of the
varactors, optimum filter characteristics are provided for
each specific operating frequency.
(6) 540 - 999 MHz Reception
Received signals between 540 and 999 MHz pass
through the high-pass filter circuit, T/R switch D1004
(
1SV271
) prior to application to RF amplifier Q1002
(
2SC5277
). The amplified RF signal is passed through a
band-pass filter to first mixer Q1010 (
2SC5277
). Mean-
while, UHF output from the VCO-UNIT is amplified by
Q1016 and applied through diode T/R switch D1045 to
mixer Q1010 as the first local signal.
The 47.25-MHz intermediate frequency product of the
mixer is delivered to the AF-UNIT.
The TUNE voltage from the CPU on the CNTL-UNIT is
amplified by DC amplifier Q3017 and applied to varac-
tors D1015 and D1017 (
HVC355B
) in the variable frequen-
cy band-pass filters. By changing the electrostatic capaci-
tance of the varactors, optimum filter characteristics are
provided for each specific operating frequency.
(7) 47.25-MHz First Intermediate Frequency
The 47.25-MHz first intermediate frequency from the
first mixers is delivered from the RF-UNIT to the AF-UNIT
through jacks J1008 and J2001. On the AF-UNIT, the IF
for AM and FM-narrow signals is passed through NAR/
WIDE switch D2001 (
DAP222
) and the 47.25-MHz mono-
lithic crystal filter (MCF) XF2001 to narrow IF amplifier
Q2002 (
2SC4915-0
) for input to pin 16 of the Narrow IF
IC Q2016 (
TA31136FN
), after amplitude limiting by D2003
(
DA221
).
Meanwhile, a portion of the output of 11.7-MHz crystal
X1001 on the RF-UNIT is multiplied fourfold by Q2004
(
2SC4915-0
) and Q2012 (
2SC4154E
) to provide the 46.8-
MHz second local signal, applied to the Narrow IF IC.
Within the IC, this signal is mixed with the 47.25-MHz
first intermediate frequency signal to produce the 450 kHz
second intermediate frequency.
This second IF is filtered by ceramic filter CF2002
(
ALFYM450F=k
) and amplified by the limiting amplifier
within the Narrow IF IC before quadrature detection by
ceramic discriminator CD2001 (
CDBM450C7
).
Demodulated audio is passed from pin 9 of the Narrow
IF IC through the "Mute" analog switch Q2029 (
2SJ364
)
and squelch gate Q2036 (
2SJ364
) before de-emphasis at
Q2028 (
DTC144EE
).
The resulting audio is amplified by AF amplifier Q2040
(
TDA7233D
) and fed through the MIC/EAR jack J2002 to
internal speaker SP1001 or an external earphone.
(8) Squelch Control
Signal components in the neighborhood of 15 kHz con-
tained in the discriminator output pass through an active
band-pass filter composed of R2059, R2060, R2062, C2076,
C2078 and the operational amplifier between pins 7 and
8 within Narrow IF IC Q2016. They are then rectified by
D2012 and D2013 (
MC2850
) to obtain a DC voltage cor-
responding to the level of noise. This voltage is fed to pin
49 of CPU Q3035 (
HD6472237TF10
), which compares the
input voltage with a previously set threshold. When the
input voltage drops below the threshold, normally due to
the presence of a carrier, the CPU turns on squelch gate
Q2036 and allows any demodulated audio to pass. At the
same time, Q3001 and/or Q3003 and/or Q3004 goes on,
causing the BUSY/TX lamp D3033 (
FRGB1312CE-10-TF
)
to light.
Transmitter Signal Flow
(1) 145-MHz-Band Transmit/Receive Switching
Closing PTT switch S2002 on the AF-UNIT pulls the base
of Q3008 (
DTA144EE
) low, causing the collector to go
high. This signal is fed to pin 33 (PTT) of CPU Q3035,
allowing the CPU to recognize that the PTT switch has
been pushed. When the CPU detects closure of the PTT
switch, pin 10 (TX) goes high. This control signal is deliv-
ered to the RF-UNIT, where it switches Q1044 (
UMW1
)
and Q1043 (
CPH6102
) to produce the TX control signal
that activates Q1046 (
2SA1774
). At the same time, PLL
division data is fed to PLL IC Q1019 (
MB15A01PFV1
)
from the CPU, to disable the receiver power saver. Also,
it switches Q1048 (
KRC654U
) to disable the receiver cir-
cuits. This causes the "red" mode of BUSY/TX lamp D3033
to light.
Summary of Contents for VX-7R
Page 5: ...5 Block Diagram ...
Page 6: ...6 Interconnection Diagram ...
Page 21: ...21 RF Unit Lot 4 Circuit Diagram ...
Page 35: ...35 AF Unit Lot 3 Circuit Diagram ...
Page 37: ...37 AF Unit Lot 4 Circuit Diagram ...
Page 47: ...47 CNTL Unit Lot 3 Circuit Diagram ...
Page 49: ...49 CNTL Unit Lot 4 Circuit Diagram ...
Page 58: ...58 CNTL Unit Note ...
Page 63: ...63 Note ...
