Dsc Encoder/ Decoder; 1050 Hz Weather Alert Decoder - Standard Horizon Quest GX1255S Service Manual

Circuit Description
lers Q1004 (2SA1602A), Q1008 (2SC4154E) and Q1012
(2SA1602A) to transmitter RF power amplifier Q1001,
thus providing positive control of the power output.
Generation of spurious products by the transmitter is min-
imized by the fundamental carrier frequency being equal
to the final transmitting frequency, modulated directly in
the transmit VCO. Additional harmonic suppression is
provided by a low-pass filter consisting of coils and ca-
pacitors, resulting in more than 70 dB of harmonic sup-
pression prior to delivery of the RF energy to the antenna.

DSC Encoder/ Decoder

Encoder
The DCS (Digital Selective Calling) encode signal which
D/A converted in the 8-bit MPU IC Q2003 is fed through
the low-pass filter Q1028 on the RF Unit to the VCO.
Decoder
The receiving DCS code is demodulated by the FM IC
Q1024, then fed through the low-pass filter Q1026
(2SC4154E) to the DCS Decoder IC Q1032 (NJM2211M)
which the receiving DCS code is decoded. The decoded
DCS signal delivered to the 8-bit MPU IC Q2003
8

1050 Hz Weather Alert Decoder

1050Hz Weather Alert signals are demodulated on the
CNTL Unit, and are applied to low-pass filter Q1026
(2SC4154E), and pass thorugh the limiter comparator
Q1028 (NJM2902M).
MPU
Operation is controlled by 8-bit MPU IC Q2003
(M37560M). The system clock uses a 9.8304 MHz crystal
for a time base. IC Q2004 (PST597CN) resets the MPU
when the power is on, and monitors the voltage of the
regulated 5V power supply line.
EEPROM
The EE-PROM retains TX and RX data for all memory
channels , prescaler dividing, IF frequency, local oscilla-
tor injection side, and reference oscillator data.