Circuit Description - Kenwood TH-28A Service Manual
144mhz fm transceiver
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Also See for TH-28A:
- Service manual (78 pages) ,
- Instruction manual (65 pages) ,
- Manual (60 pages)
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TH-28A/E
CIRCUIT DESCRIPTION
Frequency Configuration
The frequency configuration is shown in Figure 14
and Table 1.
455kH2
(1) 144.000~147.995MHz
{K, P, M, x)
CF
144,000~145.995MHz_
(T, &)
ANT
/
ma
45.05MHz
(2) 144,000~147.995MHz_
{K, P, M, X)
tstMIX
MCE
SP
444,000~145.995MHz
(T, &)
ANTSW
RE AMP
py MIX. IF.DET [mj AF AMP
(3) 189.050~193.045MHz _ {K, P, M. X)
—_
189.050~191.045MHz
(T, E)
C3 45.505MHz
ist MIX
"T
438.000~
Left RE AMP
449.995MHz
392.95 ~
MIC
404.945MHz
MIG
PA AMP
TX AMP
.
PLLVCO
ey
ANP
(|
(2)
a
= 12.6MHz
Fig. 1 Frequency configuration
Receiver
System
Receiving
Double superheterodyne system
- RE amplifier
system
1st IF frequency
45.05MHz
ee
.
2nd
IF f
ne
455kHz
The signal from the antenna is passed through a
=
.
reqveny
1
—-
-
.
Transmitting|—-——-Direct-osceillating—————-—--|---
low-pass filter and transmission/reception. selector cir-
system
amplification system
cuit, and input to the RF amplifier.
"odulation
Variable reactance
The input signal is amplified by Q213 and sent-to the
.
;
system
phase modulation
bandpass filter to eliminate the unwanted frequency
=
-
_
band.
Table 1 Basic configuration
For sub-UHF reception, the signal from the antenna
passes through the high-pass filter, and is amplified by
RF amplifier Q216.
;
Ss
7
ee
pet
HPF re)
o f assem ma nee
OL ay OG
Cement
s r ] seusemsminionsseniectenne
saints
penngeeg = gyn
bee] LPF be] ANT
[ \
DH>-
IF AMP,DET 41
&
—L
S
CI
|
=
2nd Local OSC
BSW) on
BSW) (sug
OS
Fig.2
Receiver section configuration
° First-stage mixer
.
item
Rating
The input signal is mixed with the first local oscilla-
Nominal center frequency (fo) | 45.05MHz
tor signal from the PLL circuit by first-stage mixer
Pass bandwidth
+7 5kHz2 of more at 3dB
0214 (Q217 for sub-UHF) and so is converted into the
Attenuation bandwidth
¥29kHz or less at 2508
first IF singal. The unwanted frequency
band
of the
Guaranteed attenuation
80dB or more at —910kHz
first IF signal is eliminated by a two-stage monolithic
Spurious
: 40¢B or more wthin +1MHz
crystal filter (MCF).
Ripple
| 1.0dB or less
Insertion loss
4.0dB or less
Terminal impedance
8000/2pF
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