DE
DANIELS
ELECTRONICS
2-2
MT-3 AM 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 approxi2 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 Time-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 approxi2 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
Optional Relay
The transmitter's PTT circuitry can be completely isolated by installing RELAY1. Jumpers J2 to
J4 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 energizing 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, the other set of contacts are brought out to the backplane connector.
To configure the isolated input for PTT WTO operation jumpers J2, J4 must be in the 'y'position,
J3 must be in the 'x' 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.
