41
12.4. W/K Receiving Circuit (T-1112)
RX method is a Double Super-heterodyne receiver
as such MF/HF receiving method and
1'st intermediate frequency is 49.455MHz and
2'nd is 455 KHz.
14MHz standard frequency supplied from MAIN (T-
1110) is supplied to MIXER making each
SYNTHESIZER frequency into a PCB board.
(1) Receiving signal in ANTENNA terminal pass
through input over-voltage protecting circuit and
BAND-PASS FILTER per frequency (2.187, 5 /
4.207,5 / 6.312 / 8.414,5 / 12.577 / 16.804, 5MHz)
and is closing in DSC distress safety frequency.
FILTER is response in receiving CHANNEL.
(2) Receiving signal to pass filter is amplified by
high-frequency amplifier of width band and is
supplied to 1'st MIXER (MX2) through 20MHz LOW
PASS FILTER.
The signal is mixed with 1'st local frequency (W/K
1'st LO) supplied from inner SYNTHESIZER and
converted to 1'st intermediate frequency (1'st IF)
49.455MHz and it goes through X-tal filter, IF
amplifier, then is supplied to 2'nd MIXER and in
2'nd MIXER, is mixed with 2'nd local frequency
(W/K 2'nd LO) 49MHz and converted to 2'nd
intermediate frequency (2'nd IF) 455KHz.
(3) It consists of AGC circuit controlling amplify of
IF AMP by 2'nd IF and the intermediate frequency
supplied to 3'rd MIXER is mixed with BFO signal
and demodulated to baseband signal and the
output-digitalized signal through MODEM is input to
CPU.
12.5. Power Amplifier Circuit (T-1113)
The PCB circuit consists of PA+24V Switching
circuit effected by TX+KEY signal, 2 pieces of
Drive's part, Power Amp part and after the TX
signal input from a main board (T-1110) is
sufficient amplified, sent to the TX Filter board of
MF/HF (T-1101).
12.6. Front Panel (T-1114)
The PCB circuit consists of LCD, LED, a kind of
tap-switch with a power switch, variable resistance
controlling brightness, gain receiving, volume,
channel dial and it is put into a front panel along
with the connector for inter speaker, hand Mic (SM-
1150).
