Kenwood TM-631A Service Manual page 8

TM-631A
CIRCUIT DESCRIPTION
Transmitter Circuits
¢
General
Except
for the microphone amplifier and
APC (Automatic
Power
Control) circuits, the transmitting circuits
are
independent.
MIC
AMP
(X59-3610- 00)
_
_
*
Modulation Circuit
The audio signal
from the microphone
is
fed to three opera-
tional amplifiers
which
perform
preemphasis, amplification, and
limiting, and form
a
splatter filter that removes unwanted high-
frequency components.
The modulation circuit directly modulates
the
VCO (Voltage
control oscillator) for the
144 MHz
and
220
MHz bands
by
us-
ing
a
varicap.
(See Fig. 9.)
RI6
0
W
C4.
27P
x
R7
390K
0033
4
C3
R6
(272)
033
33K .033 82K 82K 82K
a
+
|
x
>
x
+
;
°
|
o
e
To
Qi:
28c4ii6(y)
ICl
NuM45saM
144PLL
1
R5
ICs
2)
IN NC
8c
R85
MIC
ClI7
220MD1 144 MHz
TX-RX
unit
Fig.
9 Modulation
Circuit
©
Preamplifier
Stage
Circuit
A three-stage
linear amplifier
is
used
in
both the 144 MHz and
220
MHz bands. Due to its
wideband design, this
linear
am-
plifier
provides stable drive output without adjustment.
¢
Power Amplifier Circuit
The drive signal
is
fed to the power modules and amplified
to
the required levels.
It
then passes through the
TX/RX
switching
diode and
a
filter and
is
transmitted via the antenna.
Rating
Item
Symbol
Tc (°C)
Unit Conditions
S-AV17 M57774
Operating voltage
Vec 25 16 17
Current consumption lec
25 14 14
Input
power
Pin
25
Zo=ZL=500
0.6 0.6 (Vcci213.8
V)
Output power
Po
25
Zo
=ZL=500
65
55
Operating
case
tem-
Tc
(op)
°c
-30~+110 -30~+110
perature
°c
-40~+110
-40~+110
Storage temperature Tstg
Table 5 Maximum Ratings of Power Modules
¢
APC
and
SWR
(Standing Wave Retio) Protection Circuits
The
APC (automatic
transmit output control) circuit and pro-
tection circuit have independent detectors
in
both
bands. The
control circuit
is
a
common
hybrid IC.
The APC detects
the output from the power module and
feeds
the result to the hybrid
IC.
The
SWR
protection circuit extracts
a
portion of the reflected
wave generated
by antenna mismat-
ching at the CM (Capacitance Matching) coupler, detects
it,
and
feeds
the result to the hybrid IC.
The
hybrid
IC
controls the power transistor
05
:
2SD1406 (Y)
in
the drive stage, controls the drive transistor and the second
pin of
the power module, and thus varies the transmitter output.
7
TM-631A
CIRCUIT DESCRIPTION
Transmitter Circuits
¢
General
Except
for the microphone amplifier and
APC (Automatic
Power
Control) circuits, the transmitting circuits
are
independent.
MIC
AMP
(X59-3610- 00)
_
_
*
Modulation Circuit
The audio signal
from the microphone
is
fed to three opera-
tional amplifiers
which
perform
preemphasis, amplification, and
limiting, and form
a
splatter filter that removes unwanted high-
frequency components.
The modulation circuit directly modulates
the
VCO (Voltage
control oscillator) for the
144 MHz
and
220
MHz bands
by
us-
ing
a
varicap.
(See Fig. 9.)
RI6
0
W
C4.
27P
x
R7
390K
0033
4
C3
R6
(272)
033
33K .033 82K 82K 82K
a
+
|
x
>
x
+
;
°
|
o
e
To
Qi:
28c4ii6(y)
ICl
NuM45saM
144PLL
1
R5
ICs
2)
IN NC
8c
R85
MIC
ClI7
220MD1 144 MHz
TX-RX
unit
Fig.
9 Modulation
Circuit
©
Preamplifier
Stage
Circuit
A three-stage
linear amplifier
is
used
in
both the 144 MHz and
220
MHz bands. Due to its
wideband design, this
linear
am-
plifier
provides stable drive output without adjustment.
¢
Power Amplifier Circuit
The drive signal
is
fed to the power modules and amplified
to
the required levels.
It
then passes through the
TX/RX
switching
diode and
a
filter and
is
transmitted via the antenna.
Rating
Item
Symbol
Tc (°C)
Unit Conditions
S-AV17 M57774
Operating voltage
Vec 25 16 17
Current consumption lec
25 14 14
Input
power
Pin
25
Zo=ZL=500
0.6 0.6 (Vcci213.8
V)
Output power
Po
25
Zo
=ZL=500
65
55
Operating
case
tem-
Tc
(op)
°c
-30~+110 -30~+110
perature
°c
-40~+110
-40~+110
Storage temperature Tstg
Table 5 Maximum Ratings of Power Modules
¢
APC
and
SWR
(Standing Wave Retio) Protection Circuits
The
APC (automatic
transmit output control) circuit and pro-
tection circuit have independent detectors
in
both
bands. The
control circuit
is
a
common
hybrid IC.
The APC detects
the output from the power module and
feeds
the result to the hybrid
IC.
The
SWR
protection circuit extracts
a
portion of the reflected
wave generated
by antenna mismat-
ching at the CM (Capacitance Matching) coupler, detects
it,
and
feeds
the result to the hybrid IC.
The
hybrid
IC
controls the power transistor
05
:
2SD1406 (Y)
in
the drive stage, controls the drive transistor and the second
pin of
the power module, and thus varies the transmitter output.
7