Circuit Description - Kenwood TH-22A Service Manual

TH-22A/AT/E
CIRCUIT DESCRIPTION
FREQUENCY CONFIGURATION
The frequency configuration is shown in Figure 1 and Tabie 1.
(1) 144.000 to 147.995 MHz (K, P, M1-4, X)
144,000 to 145.995 MHz (T, E, M5)
oe (2) 189.05 to 193.045 MHz (K, P, M1-4, X)
ANT 189.05 to 191.045 MHz (T, E, Md)
Y 45.05MHz
(1) tstMIX MCF SP
ANT'SW ; Double superheterodyne
{ b—
RF AMP MIX, IF,DET F->] AF AMP Receiving system
a system First JF 45.05 MHz
So 44.595MHz Second IF | 455 kHz
Transmitting { Direct conversion oscillating
system amplification systern
(2) Mic Modulation Variable reactance phase
PA AMP
TX AMP
I pLLVco
be MIC —(]
system
modulation
1 2 2 — Table 1 Basic configuration
(J 12.8MHz
Fig. 1 Frequency configuration
RECEIVER SYSTEM
ANT
BP F MCF IF AMP AF AMP
tit R oo Li2Lt3 ey R XFA att Ic4 1C208 SP
upr fefantswEe/ | [\ [\ IF AMP,DET paid
i 3R i T 3R 2nd Local OSC
: 1st Local OSC
cv
(PLL)
PLL Nore)
Q5
TUNING VOLTAGE
Fig. 2 Receiver section configuration
« RF amplifier
The signal from the antenna is passed through a low-pass
filter and the transmission/reception selector circuit, and in-
put to the RF amplifier. The input signal is amplified by Q9.
The unwanted frequency band of the signal is then elimi-
nated by a band-pass filter.
This band-pass filter is a variable filter using a varicap,
and operates so that it tunes to the receive frequency with
the tuning voltage that is in proportion to the PLL lock volt-
age.
e First-stage mixer
The input signal is mixed with the first local oscillator
signal from the PLL circuit by the first-stage mixer Q8, pro-
ducing a first IF signal. The unwanted frequency band of the
first IF signal is eliminated by a two-stage monolithic crystal
filters (MCF).
Item Rating
Nominal center fre- 45.05 MHz
quency (fo)
Passband width +7.5 kHz or more at 3 dB
Attenuation band width |_ +22 kHz or less at 25 dB
Guaranteed attenuation | 80 dB or more at £910 kHz
Spurious: 40 dB or more within +1 MHz!
Ripple 1dB or iess
insertion loss 4 dB or less
Terminating impedance | 800 0/2 PF
Table 2 MCF (L71-0409-05) characteristics (TX-RX unit XF1)
5