Specifications

adjusted (amplified) by IC416-B. The amplitude-adjusted signal goes to pin 2 of the DB-15

connector (CON401).

Audio signals are inputted to the 300Hz High pass filter (IC408) to eliminate sub-audible voice

products through IC409. The output of the HPF is switched by IC406-A and de-emphasized by

resister R471 and C452. After that, its level is adjusted by RV401 and then that is amplified by

IC412 (LM386 : Audio amplifier). The amplified signal goes to pin 9 of CON401 (DB-15).

ANALOG SWITCH

IC409 (MC14053B) is a digitally controlled analog switch which internally consists of three

single pole, double throw switches. By placing a high (5V) or low (0V) on the control lines which

consists of A, B and C. A controls the X ports, B controls the Y ports and C controls the Z ports.

Example: A high on control A would connect X to X1. A low on control A would connect X to X0.

HIGH PASS FILTER

The 300Hz high pass filter is an 8-pole 1dB Chebeyshev active filter that comprises of IC410

and associated components. Received audio is passed to IC408 from Pin 4 of IC409 where

sub-audible tones below 300Hz are removed. Tx (Mic) audio is also fed into IC408 via IC 409

(Pin 4) where sub-audible voice products below 300Hz are also removed.

CTCSS/DCS DECODE CIRCUITS

Discriminated audio from Pin 9 of IC6 is fed into IC411-B and associated parts which are the

first 2 poles are part of a 6th order 250 Hz Chebeyshev low pass filter. The output from pin 1

(IC411-B) is fed into IC409 (Pin 2) and outputs to pin 15 (IC409). The signal is then fed to Pin 8

(IC410) which is a 6th order low pass Butterworth switched capacitor filter. The output from the

Butterworth filter (Pin 3 of IC410) is then fed to the remaining second 4 poles part of the 6th

order Chebeyshev filter, which consist of IC411-D and one of the two internal operational

amplifiers of IC410 (MSNBLPS) along with associated components. Both the Chebeyshev and

the Butterworth combines for a 4dB ripple low pass filter when programmed for 250 Hz. The

output of IC411-D (Pin 14) is fed into the remaining internal operational amplifier of IC410

(MSNBLPS) which forms the squaring circuit for the signal decode. The signal is out from Pin 2

of IC411 (MSNBLPS) and fed into IC401 (MCU) where it is compared whether that is matched

with preprogrammed data or not. If matched, valid data is decoded, shown by a green L.E.D.

on the top panel of the radio, and audio is released through pin 9 of DB-15 Connector. If