HYT TC-268, Service Manual

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TC-268/368 Service Manual
9
Circuit Description
1. Frequency configuration
The receiver utilizes double conversion superheterodyne. The first IF is 38.85MHz and the second IF
is 450kHZ. The first local oscillator signal is supplied from the PLL circuit.
The PLL circuit in the transmitter generates the necessary frequencies. Fig.1 shows the frequencies.
TC-268 frequency range: TC-268(1): 136MHz
～
150MHz
TC-268(2): 150MHz
～
174MHz
TC-368 frequency range: TC-368(1): 400MHz
～
420MHz
TC-368(2): 450MHz
～
470MHz
B
C C
B
ANT
ANTSW
RF
MCF
38.85MHz
CF
450KHz
SYSTEM
AF
SP
X3
multiply
IF
TCXO 12.8MHz
MIC
AMP
MIC PLL
VCO
RX
TX
TX
AMP
PA
AMP
AMP AMP
Fig. 1. Frequency configuration
2. Receiver
The receiver employs double conversion superheterodyne.
1-a) Front-end RF amplifier (TC-268)
An input signal from the antenna is applied to an RF amplifier (Q203) after passing through a
transmit/receive switch circuit (D 102 and D103 are off) and a band pass filter (L208, L209 and L210).
After the signal is amplified (Q203), the signal is filtered through a band pass filter (L203 and L214) to
eliminate unwanted signals before it is passed to the first mixer. Band pass filters (L208, L209, L210,
L203 and L214) have varactor diodes (D203, D204, D206, D202 and D201). The voltage of varactor is
provided by the MPU (IC403) center frequency of the band pass filter. (See Fig. 2-a)
B
C C
B
ANT
D102
D103
BPF
Q203
RF AMP
L208-L210
BPF
L214L215
MCF
XF200
IF AMP
Q201
MIXER
Q202
CF200
IF.MIX
IC200
AF AMP
LPF.HPF
IC300
AF PA AMP
IC302
SP
WIDE/NARROW SW
Q303
X3
multiply
Q1
TCXO
1st Local OSC
(PLL)
TUNE
APC
IC403
MCU
Fig. 2-a.
Receiver configuration