Parts List

Transmitter Main Board Instruction Manual 2-1
2 THEORY OF OPERATION
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2.1 Transmitter Main Board
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2.1.1 General
Switch SW1 on the Front Panel Board is a DPDT switch which controls the operation of the
transmitter (refer to the operations section of the Transmitter Manual). When SW1 is in the 'OFF'
position the transmitter is turned off; however, +13.8 Vdc is still present on the Transmitter Main
Board as the +13.8 Vdc supply is not switched. When SW1 is in the 'KEYED' position, +9.5 Vdc
is supplied to the transmitter circuitry and the transmitter is continuously keyed on. When SW1 is
in the 'NORM' position, +9.5 Vdc is supplied to the transmitter circuitry and the transmitter can be
keyed from any of the several Push-To-Talk inputs.
Refer to section 5.2.3 Transmitter Main Board Schematic Diagram.
2.1.2 Transmitter Push-To-Talk
All three of the Push-To-Talk (PTT) inputs that key the transmitter are active low (< +2 Vdc). One
PTT input is on the front panel microphone connector. The other two PTT inputs: PTT WTO
(PTT With Time-Out-Timer) and PTT NTO (PTT No Time-Out-Timer), are on the backplane
connector of the transmitter board. If required, the microphone's PTT input can be configured to
activate the transmitter's Time-Out-Timer (TOT). An isolated PTT input can be made available by
installing an optional relay (RELAY1) and configuring jumpers J1 to J4 so that the relay controls
the PTT circuitry.
2.1.2.1 Microphone PTT
Jumper J1 on the MT-3 Front Panel Board configures the microphone's PTT input (MIC PTT) to
either bypass or activate the transmitter's TOT. Installing surface mount jumper J1 in the 'x'
position (default) selects the MIC PTT NTO line which bypasses the TOT. Installing surface
mount jumper J1 to the 'y' position selects the MIC PTT WTO line which activates the transmitter's
TOT. When SW1 is in the 'KEYED' position the MIC PTT NTO line is a utomatically grounded.
Refer to Section 5.3.1, "MT-3 Front Panel Board Component Layout" for the location of jumper
J1.