Vertex Standard VX-131 Service Manual page 11

Fm business two-way radio, vhf model

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Circuit Description

Receive and transmit buses select which VCO is made

active by Q1002 and Q1004 (both RT1N441U). TCXO unit

X1001 yields frequency stability of ±2.5 ppm @ –30 °C to

+60 °C.

Push-To-Talk Transmit Activation

The PTT switch S1002 is connected to pin 48 of micropro-

cessor Q1013 (M37516F8HP), so that when the PTT switch

is closed, pin 23 of Q1013 (M37516F8HP) goes low. This

signal disables the receiver by disabling the 5 V supply

bus at Q1025 (DTB123EK) to the front-end, FM IF sub-

system IC Q1040 (TA31136FN), and receiver VCO circuit-

ry.

At the same time, pin 22 of Q1013 (M37516F8HP) goes

high to activates the transmit 5V supply line at Q1021

(FMW1) and Q1020 (CPH6102) to enable the transmitter.

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Vx-132