Kenwood TM-221A Service Manual page 2

CIRCUIT DESCRIPTION
TM-221A (45W)
K [ mi [m2
TM-221ES (45w)
11 | mz | lw
Final unit X45-1360-02
X45-1330-03 X45-1360-02
Control unit
X53-3040-1 1 [x53-3040-21 [ X53-3040-22 X53-3040-51
X53-3040-61 | X53-3040-51 | X53-3040-61
TX-RX unit X57-3060-11
X57-3060-51 X57-3060-52
Table 1 Comparison of TM-221A, TM-221E and TM-221ES
Frequeny configuration
The TM-221A/E/ES utilize a PLL synthesizer system
incorporating a digital VFO. (See Fig. 1.) The channel
step can be selected as 5, 10, 12.5 (T,W), 15, 20, or 25kHz.'
The receiver operates as a double conversion system. Re-
ceived signals are mixed with the first local oscillator
(133.305~137,300MHz (K,M), 133,300~135.295MHz
(T,W)) to produce the first intermediate frequency of
10,.695MHz (K,M), 10.7MHz (T,W). The first intermediate
frequency is mixed with the second local oscillator (10.24
MHz (K,M), 10.245MHz (T,W)) to produce the second
intermediate frequency of 455kHz.
The transmitter system consists of a PLL circuit in-
corporating a direct oscillator and direct divider. The
output is amplified by a linear amplifier prior to being
transmission.
144~148MHz (iM)
144~146MHz (T,W)
1st MIX
133.305~
Receiver system
@ General
Incoming signals from the antenna pass through a low-
pass filter in the Transmitter Final unit and a diode trans-
mit/receive switch, then enter the receiver front end.
After passing through two antenna coils the signals are
amplified by a GaAs (galium arsenide) FET (Q1
3SK184(S). Undesired signals are removed by 3 tuning
coils (L19~L21 : K,M) or a 3-pole helical resonator (L3 :
TW). The resulting signal is applied to the first mixer
Q2 : 3SK131(V12), which employs an N channel MOS FET
to obtain good 2-signal characteristics. In the first mixer
(Q2) the signal is mixed with the first local oscillator
from the PLL system to produce the first IF signal of
10.695MHz (K,M), 10.7MHz (T,W). Interfering Adjacent
channel interference is removed from the first IF signal
by a two-stage monolithic crystal filter (MCF) (L6).
455kHz
CFW455F
10.7MHz (TW) co 10.24MHz (KM)
137.300MHz {K,M)
133.300~
T
10.245MHz
(T,W)
135,.295MHz (T,W)
'Sams eae
TT 7
PLL |
SYSTEM |
L.
a _Jj
MIC
144,000~
147.995MHz (KM)
144.000~
145.S95MHz (T,W)
Fig. 1 Frequency configuration