Parts List

2-2 Transmitter Main Board Instruction Manual
2.1.2.2 PTT With Time-Out-Timer
Pins B10 and Z10 of the backplane connector are the PTT WTO input. When the PTT WTO
signal, which is normally high, falls below +2.0 Vdc, the transmitter is keyed. The transmitter is
disabled when the PTT WTO input rises above +2.3 Vdc or if the TOT's time-out period is
exceeded. If the time-out period is exceeded the PTT WTO input must go high (>+2.3 Vdc) and
then low again in order to rekey the transmitter.
The PTT WTO threshold of approximately +2 Vdc (0.3 Vdc hysteresis) is set by U1a, R1, R2, R3,
R4, R9, and R10 while diodes D1 and D2 provide overvoltage protection for U1a. The PTT WTO
signal output from U1a is 'AND'ed with the MIC PTT WTO by U2a. When either the PTT WTO
or the MIC PTT WTO is activated the output of U2a goes low which triggers the transmitter's TOT
located on the MT-3 Audio Processor. The TOT's output is 'AND'ed with the MIC PTT NTO
signal (U2c) and the PTT NTO signal (U2d). When any one of the preceding three signals (TOT's
output, MIC PTT NTO, PTT NTO) go low the transmitter is activated by transistors Q1 to Q7
which switch power to the various modules.
2.1.2.3 PTT No Tim e-Out-Timer
Pins B14 and Z14 of the backplane connector are the PTT NTO input. When the PTT NTO signal,
which is normally high, falls below +2.0 Vdc, the transmitter is keyed. As long as the PTT NTO
signal remains below +2.0 Vdc the transmitter will remain keyed. The transmitter is disabled when
the PTT NTO signal rises above +2.3 Vdc.
The PTT NTO threshold of approximately +2 Vdc (0.3 Vdc hysteresis) is set by U1b, R5, R6, R7,
R8, R9, and R10 while diodes D3 and D4 provide overvoltage protection for U1b. The PTT NTO
signal is 'AND'ed with the output of U2c (MIC PTT NTO signal 'AND'ed with the TOT output) by
U2d. When the output of U2d goes low the transmitter is activated by transistors Q1 to Q7 which
switch power to the various modules.
2.1.2.4 Op tional Relay
The transmitter's PTT circuitry can be completely isolated by installing RELAY1. Jumpers J1 to J5
configure the relay to provide an isolated PTT input for either the PTT WTO line or PTT NTO line.
The isolated PTT input is enabled by energiz ing the relay. The transmitter board will accept any of
the Aromat TF2E line relays. These relays are DPDT, single side stable, and have coil voltages
ranging from +3 Vdc to +48 Vdc. Only one set of relay contacts are used to activate the PTT
circuitry.
To configure the isolated input for PTT WTO operation jumpers J2, J3, and J4 must be in the 'y'
position. In this mode, pins B10 and Z10 no longer function as the PTT WTO input; however, pins
B14 and Z14 continue to function as the normal PTT NTO input.