Kenwood TM-631A Service Manual page 4

TM-631A
CIRCUIT DESCRIPTION
Receiver Circuits
¢ General
This set uses seperate receiver circuits
for the
144 MHz
and
220 MHz bands. These circuits extend from the antenna in-
put
section
to the
IF
detector.
©
144 MHz
The incoming two meter band signal passes thru the trans-
mit/receive switching diode
in
the final unit. And then through
the antenna matching coil
in
the front unit.
It
is then amplified
by
a
GaAs FET radio-frequency
amplifier, Filtered by
a
three-
stage bandpass
filter that
uses varicap tuning
to
reject unwant-
ed
signal components, and is fed to the first mixer. There
it
is
mixed with the first local oscillator signal from the
PLL
to
generate the first
IF
signal
(16.9
MHz). Spurious adjacent-
channel signals are removed
in a
two-stage MCF (Monolithic
Crystal Filter).
The first
IF
signal
is
amplified and fed to the FM
IF
IC:MC3361D.
This
IF
signal
is
mixed with the second ocal oscillator frequency
of
17.355 MHz which
results
in
a
second
IF signal of
455
kHz.
Spurious adjacent-channel signals
are removed from the se-
cond
IF
signal by ceramic filter. Then the signal
is
amplified
and
detected
to
generate the audio signal.
Q!
RA2
16
02
G2
08
6
PLL
OUT
Fig.
2
144 MHz
Front End
(Varicap Tuning)
¢
220
MHz
band
The incoming
220
MHz signal passes
thru
the transmit/receive
antenna switching diodes
in
the final unit and then passes
through the antenna matching coil.
It
is
then amplified by
a
GaAs FET
radio-frequency amplifier.
Filtered by
a
three stage
bandpass
filter that uses
varicap tuning
to reject unwanted
sig-
nal components,
and enters the first mixer,
where
it
is
mixed
with the first local oscillator signal from the
PLL
to generate
the first
IF
signal
(30.825
MHz). Spurious adjacent-channel sig-
nals are removed by
a
two-stage MCF.
The
first
IF
signal
is
amplified and fed to the FM
IF IC
(MC3361D). This
IF
signal
is
mixed with
a
second ocal oscil-
lator
frequency
of
30.37 MHz which converts
it
to
a
second
IF
signal of
455
kHz.
Spurious adjacent-channel signals
are
removed from the se-
cond
IF
signal by an ceramic filter. The signal
is
then amplified
and detected
to
generate the audio signal.
Item
Specification
Nominal center frequency
30.825
MHz
Pass bandwidth
Max. + 7.5 kHz at
3
dB
Attenuation
band
width Max.
+28
kHz at 40
dB
Ripple
Max. 1.5
dB
Insertion loss Max. 3 dB
Guaranteed attenuation
60
dB or
greater at +
1
MHz;
40
dB or greater for spurious signal
Terminating impedance
1.4
kQ/1
pF
Table 2
MCF (L71-0270-05) Characteristics
(220 MHz
TX-RX
Unit
XF1)
Item Specification
Nominal
center frequency
455 kHz+
1
kHz
6
dB
bandwidth Min.
+6
kHz (above
455
kHz)
50 dB bandwidth
Min.
+ 12.5
kHz (above 455
kHz)
Ripple
(455
+4
kHz)
Max. 3 dB
Insertion loss Max. 6 dB
Guaranteed attenuation
Max. 35 dB
(455
+100
kHz)
Input-output matching
2.0
kQ
impedance
02
Table
3
Ceramic Filter
CFW455F (L72-0315-05)
Characteristics (220 MHz
TX-RX
Unit CF1,
144MHz
TX-RX
Unit
CF1)
Item
Rating
Nominal
center frequen-
16.900 kHz
cy (fo)
3 dB bandwidth
+ 7.5
kHz
or more
Attenuation bandwidth
+25
kHz
or
less at
40
dB
+45
kHz or less at
60
dB
Guaranteed attenuation 70
dB or more
within +
1
MHz
(Sprious response
40
dB or more)
80
dB
or more
within fo
-
(900~ 920
kHz)
Ripple
1.0
dB or less
Loss 1.5
dB or
less
Input and output im-
1.8
kQ/O pF
pedance
Table
4 MCF (L71-0279-05)
Characteristics
(14
MHz
TX-RX
Unit XF1)
3
TM-631A
CIRCUIT DESCRIPTION
Receiver Circuits
¢ General
This set uses seperate receiver circuits
for the
144 MHz
and
220 MHz bands. These circuits extend from the antenna in-
put
section
to the
IF
detector.
©
144 MHz
The incoming two meter band signal passes thru the trans-
mit/receive switching diode
in
the final unit. And then through
the antenna matching coil
in
the front unit.
It
is then amplified
by
a
GaAs FET radio-frequency
amplifier, Filtered by
a
three-
stage bandpass
filter that
uses varicap tuning
to
reject unwant-
ed
signal components, and is fed to the first mixer. There
it
is
mixed with the first local oscillator signal from the
PLL
to
generate the first
IF
signal
(16.9
MHz). Spurious adjacent-
channel signals are removed
in a
two-stage MCF (Monolithic
Crystal Filter).
The first
IF
signal
is
amplified and fed to the FM
IF
IC:MC3361D.
This
IF
signal
is
mixed with the second ocal oscillator frequency
of
17.355 MHz which
results
in
a
second
IF signal of
455
kHz.
Spurious adjacent-channel signals
are removed from the se-
cond
IF
signal by ceramic filter. Then the signal
is
amplified
and
detected
to
generate the audio signal.
Q!
RA2
16
02
G2
08
6
PLL
OUT
Fig.
2
144 MHz
Front End
(Varicap Tuning)
¢
220
MHz
band
The incoming
220
MHz signal passes
thru
the transmit/receive
antenna switching diodes
in
the final unit and then passes
through the antenna matching coil.
It
is
then amplified by
a
GaAs FET
radio-frequency amplifier.
Filtered by
a
three stage
bandpass
filter that uses
varicap tuning
to reject unwanted
sig-
nal components,
and enters the first mixer,
where
it
is
mixed
with the first local oscillator signal from the
PLL
to generate
the first
IF
signal
(30.825
MHz). Spurious adjacent-channel sig-
nals are removed by
a
two-stage MCF.
The
first
IF
signal
is
amplified and fed to the FM
IF IC
(MC3361D). This
IF
signal
is
mixed with
a
second ocal oscil-
lator
frequency
of
30.37 MHz which converts
it
to
a
second
IF
signal of
455
kHz.
Spurious adjacent-channel signals
are
removed from the se-
cond
IF
signal by an ceramic filter. The signal
is
then amplified
and detected
to
generate the audio signal.
Item
Specification
Nominal center frequency
30.825
MHz
Pass bandwidth
Max. + 7.5 kHz at
3
dB
Attenuation
band
width Max.
+28
kHz at 40
dB
Ripple
Max. 1.5
dB
Insertion loss Max. 3 dB
Guaranteed attenuation
60
dB or
greater at +
1
MHz;
40
dB or greater for spurious signal
Terminating impedance
1.4
kQ/1
pF
Table 2
MCF (L71-0270-05) Characteristics
(220 MHz
TX-RX
Unit
XF1)
Item Specification
Nominal
center frequency
455 kHz+
1
kHz
6
dB
bandwidth Min.
+6
kHz (above
455
kHz)
50 dB bandwidth
Min.
+ 12.5
kHz (above 455
kHz)
Ripple
(455
+4
kHz)
Max. 3 dB
Insertion loss Max. 6 dB
Guaranteed attenuation
Max. 35 dB
(455
+100
kHz)
Input-output matching
2.0
kQ
impedance
02
Table
3
Ceramic Filter
CFW455F (L72-0315-05)
Characteristics (220 MHz
TX-RX
Unit CF1,
144MHz
TX-RX
Unit
CF1)
Item
Rating
Nominal
center frequen-
16.900 kHz
cy (fo)
3 dB bandwidth
+ 7.5
kHz
or more
Attenuation bandwidth
+25
kHz
or
less at
40
dB
+45
kHz or less at
60
dB
Guaranteed attenuation 70
dB or more
within +
1
MHz
(Sprious response
40
dB or more)
80
dB
or more
within fo
-
(900~ 920
kHz)
Ripple
1.0
dB or less
Loss 1.5
dB or
less
Input and output im-
1.8
kQ/O pF
pedance
Table
4 MCF (L71-0279-05)
Characteristics
(14
MHz
TX-RX
Unit XF1)
3