Kenwood TM-321A Service Manual page 4

TM-321A TM-321A
CIRCUIT DESCRIPTION
CIRCUIT DESCRIPTION
a
The first IF
signal
is
amplified by Q3
:
2SC2714(Y)
ey
6
and fed to
a
special
narrow-FM
IC
(TA7761F).
Here the
7
<
signal
is
mixed with
the
30.370MHz
frequency from the
4°
second local oscillator to produce the 455kHz
second
IF
3
2
3
3
signal.
This
signal
is sharpened by passing it through a six- S
8
element ceramic filter (CFW455F). The
signal
is then
5
&685
amplified by a five-stage jimiting amplifier contained in
2
IC1. This
is
followed by quadrature detection which
is
B588
also performed
by IC1. Undesirable high-frequency com-
or
-114
u
24 2
ponents
are removed from the detected
signal
by an
active
Table
1
MCF (L71-0270-05)
characteristics
42
2
SREES
3
low-pass
filter. The signal then
passes
through the audio
(TX-RX
unit L6)
ae
oN0
volume
control,
then
is
amplified by the audio power amp-
aon
WA
Se
lifier (IC4), and apptied to the
speaker.
The circuit con-
3
EP)
SS,
+
Terars
figuration from detection onward is shown in Fig. 2.
9
» ae
ww
®
Squelch circuit
55
o
2 0 *
£
SOs
The
noise component extracted from the detector out-
2 39
9
put is
filtered to
remove the second intermediate fre-
Bs NO 2
z
&=
quency component
(455kHz), amplified twice, and
is
then
ue
me"
fed to the rectifier.
After rectification,
the signal
passes <6
88
»
wD
through the squelch control to the audio limiter circuit,
€
g
22
5
aq
© S-meter circuit
ZEN
2
*
a
The S-meter output voltage of the special narrow-FM
N
5
&
iC (TA7761F)
is amplified by an inverting amplifier,
s
"
3 8
fed
to the Control unit The mieroprocessor converts
Table
2 Ceramic fitter CFW455F (L72-0315-05)
©
ae
a
the analog voltage to
a
digital
signal
that
is
useddto
contro
characteristics
(TX-RX
unit L10)
6
the LCD
bar meter.
3
083
>
2
0
orée
+
ue
5
g
3
0
a
>
E
by
SY
3
Bs
0
=
3
a
a
oo
Item
Rating
Nominal center frequency
(fo)
30.825MHz
Pass
bandwidth £7.5kHz or more at 3dB
Attenuation bandwidth *28kHz
or
ess
at 40dB
60dB or more within +1MHz
Guaranteed attenuation
40dB or more squrious
Ripple 1.50B or ess
insertion
loss
3dB or less
Terminating impedance
1.4k2/1PF
03
oN
oso
3
Fig. 2 Circuits from detector output onward
Item
Rating
Nominal center frequency 455kHz+1kHz
6dB bandwidth +6kHz
or more (from 455kHz)
50dB bandwidth +12,5kHz or
less (from
455k Hz}
Ripple
(within
455+4kHz)
3dB or less
Insertion loss 6dB or ess
Guaranteed attenuation
35dB
or less
(within 4554100kHz)
1/0 impedance
2.0k2
sa
then
ay
b
oro
an
seu
ao
eo
eu
oz
TM-321A TM-321A
CIRCUIT DESCRIPTION
CIRCUIT DESCRIPTION
a
The first IF
signal
is
amplified by Q3
:
2SC2714(Y)
ey
6
and fed to
a
special
narrow-FM
IC
(TA7761F).
Here the
7
<
signal
is
mixed with
the
30.370MHz
frequency from the
4°
second local oscillator to produce the 455kHz
second
IF
3
2
3
3
signal.
This
signal
is sharpened by passing it through a six- S
8
element ceramic filter (CFW455F). The
signal
is then
5
&685
amplified by a five-stage jimiting amplifier contained in
2
IC1. This
is
followed by quadrature detection which
is
B588
also performed
by IC1. Undesirable high-frequency com-
or
-114
u
24 2
ponents
are removed from the detected
signal
by an
active
Table
1
MCF (L71-0270-05)
characteristics
42
2
SREES
3
low-pass
filter. The signal then
passes
through the audio
(TX-RX
unit L6)
ae
oN0
volume
control,
then
is
amplified by the audio power amp-
aon
WA
Se
lifier (IC4), and apptied to the
speaker.
The circuit con-
3
EP)
SS,
+
Terars
figuration from detection onward is shown in Fig. 2.
9
» ae
ww
®
Squelch circuit
55
o
2 0 *
£
SOs
The
noise component extracted from the detector out-
2 39
9
put is
filtered to
remove the second intermediate fre-
Bs NO 2
z
&=
quency component
(455kHz), amplified twice, and
is
then
ue
me"
fed to the rectifier.
After rectification,
the signal
passes <6
88
»
wD
through the squelch control to the audio limiter circuit,
€
g
22
5
aq
© S-meter circuit
ZEN
2
*
a
The S-meter output voltage of the special narrow-FM
N
5
&
iC (TA7761F)
is amplified by an inverting amplifier,
s
"
3 8
fed
to the Control unit The mieroprocessor converts
Table
2 Ceramic fitter CFW455F (L72-0315-05)
©
ae
a
the analog voltage to
a
digital
signal
that
is
useddto
contro
characteristics
(TX-RX
unit L10)
6
the LCD
bar meter.
3
083
>
2
0
orée
+
ue
5
g
3
0
a
>
E
by
SY
3
Bs
0
=
3
a
a
oo
Item
Rating
Nominal center frequency
(fo)
30.825MHz
Pass
bandwidth £7.5kHz or more at 3dB
Attenuation bandwidth *28kHz
or
ess
at 40dB
60dB or more within +1MHz
Guaranteed attenuation
40dB or more squrious
Ripple 1.50B or ess
insertion
loss
3dB or less
Terminating impedance
1.4k2/1PF
03
oN
oso
3
Fig. 2 Circuits from detector output onward
Item
Rating
Nominal center frequency 455kHz+1kHz
6dB bandwidth +6kHz
or more (from 455kHz)
50dB bandwidth +12,5kHz or
less (from
455k Hz}
Ripple
(within
455+4kHz)
3dB or less
Insertion loss 6dB or ess
Guaranteed attenuation
35dB
or less
(within 4554100kHz)
1/0 impedance
2.0k2
sa
then
ay
b
oro
an
seu
ao
eo
eu
oz