Vertex Standard VXA-150, Service Manual

Page: 13 / 32

13
Circuit Description
Push-To-Talk Transmit Activation
The PTT switch on the microphone is fed through the
PTT controller, Q1002 (
UMZ2N
), to pin 41 of micropro-
cessor Q1014 , so that when the PTT switch is closed, pin
18 of Q1014 goes high. This signals the microprocessor to
activate the TX/RX controller Q1017 (
UMG2N
), which cut
off the receiver by disabling the 5 V supply bus at Q1020
(
DTA143EU
) which feeds the front-end, FM IF subsystem
IC Q1049 , and receiver VCO circuitry. At the same time,
Q1037 (
UMW1
) and Q1041 (
DTA143EU
) activates the
transmit 5 V supply line to enable the transmitter.