SECTION 3 CIRCUIT DESCRIPTION
3-1
RECEIVER CIRCUITS
3·1·1 HF/50 MHz
RF
CIRCUIT (FILTER AND
MAIN UNITS, HPF BOARD)
HF/50
MHz
RF
filters pass only the desired band signals
and
suppress any undesired
band
signals. The HF/50
MHz
RF
circuit has 7 low-pass filters and 6 high-pass filters for
specified
band
use.
HF/50
MHz
RF
signals from the [ANT1] connector, pass
through one of 7 low-pass filters
as
below, the transmit!
receive switching relay (RL1)
and
low-pass filter (L
1,
L2,
C1-C5),
and
are then applied to the
MAIN
unit via
P1
(MAIN
unit J1).
Used RF low-pass
filter
(FILTER unit)
Band
Control Input
Band
Control Input
signal relay signal relay
0.03-2
MHz
L1
RL15
15-22
MHz
L5
RL11
2-4
MHz
L2
RL13
22-30
MHz
L6
RL7
4-8
MHz
L3
RL5
30-60 MHz
L7
AL3
8-15 MHz
L4
RL9
The signals from the FILTER unit are applied
to
or bypass
the 20
dB
attenuator
(A3,
R4,
01,
01). The signals pass
through the high-pass filter (L3-L7, C3-C7, R5-R7) to
suppress strong signals below 1.6
MHz
and
are then
applied to the HPF board via the
"TOAT" terminal.
(1) 0.03-2
MHz
and 30-40
MHz
The signals pass through a low-pass filter (L23,
L24,
C38-
C42), bypass the high-pass filters via
05
and
are then
applied to the preamplifier circuit.
(2)
2-30
MHz
The signals pass through the low-pass filter
(L23,
L24,
C38-C42). The filtered signals are applied to one of 5
high-pass filters
as
at right above
and
are then applied to
the preamplifier circuit.
• RECEIVER CONSTRUCTION
(3)
40-60 MHz
The signals pass through the high-pass filter (L29-L31,
C47-G51) via 012
and
are then applied to the preamplifier
circuit.
Used RF high-pass filter (HPF board)
Band
Control Input
Band
Control Input
signal diode signal diode
0.03-2
MHz
TH
05
15-22
MHz
H5
021
2-4
MHz
H2
016
22-30 MHz
H6
07
4-8
MHz
H3
020
30-40 MHz
TH
05
8-15
MHz H4 017
40-60
MHz
BV,
T8
012
3·1·2 VHF
RF
CIRCUIT (PA UNIT)
VHF AF bandpass filters pass only the desired band signals
and suppress any undesired band signals. The VHF AF
circuit has 2 bandpass filters.
VHF AF signals from the [ANT2] connector, pass through a
low-pass filter, antenna switching circuit (04, 014, 015) and
one of 2 bandpass filters. The signals within 144-148
MHz
pass through one bandpass filter (L29,
L30,
C45-C49)
and
the signals within 60-144
MHz
or 148-200
MHz
pass
through another bandpass filter (L25,
L26,
L40, L49,
C52-
C57, C151-C154).
The filtered signals pass through the AF attenuator (A27,
024), are amplified at the
AF
amplifier (IC1), applied to the
MAIN
unit via
P2
(MAIN
unit J3)
and
are then applied
to
the
preamplifier circuit
in
the
HPF
board.
3·1·3 PREAMPLIFIER CIRCUIT (HPF BOARD)
The preamplifier circuit
in
the IC-70a has approx. 15
dB
gain
over a wideband frequency range.
_
.......••
------~
..
_.
__
._--~_
..----_..-
_-
I
IANT2
J
PA
unit
60-200
MHz
a----
AMP>-----...J
FILTER
unit
:
MAIN
unit
2nd LO;
aO.OMHz
ToWFM
detector (IC9)
BFO;
9.0115 MHz
~
TOAF
selector
switch
Product (IC1S)
detector
lela
To FM detector
(IC1S)
To AM detector
(044)
3
-1
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