Parts List

Transmitter Main Board Instruction Manual 2-5
Z18 by a transformer (T1). Two audio outputs from the MT-3 Audio Processor are routed to the
synthesizer or crystal control oscillator modules.
2.1.3.1 Microphone Audio
Normally the audio from a transmitt er's microphone is transmitted by that transmitter; however, the
Transmitter Main Board can be configured by the MIC IN and MIC OUT lines so that the audio
from an external microphone modulates transmitter. The configuration of the MIC IN (pin Z4) and
MIC OUT (pin B4) lines on the MT-3 Transmitter Board are controlled by jumpers J16 and J17
respectively. Jumper J16 selects the audio source for the MT-3 Audio Processor's microphone
input. Jumper J17 is used to enable or disable the MIC OUT line. Normally the transmitter's
microphone is selected (J16 in the 'x' position) and the MIC OUT line is enabled (J17 is installed).
2.1.3.2 Received Audio
Pin B20 is the audio input from the transmitter's corresponding receiver. The default setting for
this line is to have it AC coupled (Jumper J9 is out) and directly connected to the front panel board
RX AUDIO line (jumpers J10 and J11 in the 'x' position). Audio amplifier U5 can be enabled by
installing jumper J8 which connects power to U5 (continuously in the 'x' position, PTT switched in
the 'y' position). Setting jumper J10 in the 'y' position and jumper J11 in the 'z' position enables the
audio path through the amplifier. Level control for the squelched, de-emphasized audio input line is
provided by R27. Audio amplifier U5 draws approximately 5 mA so it is not normally enabled.
2.1.4 Channel Selection
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2.1.4.1 Synthesized Transmitter
Seven backplane connections are used to communicate with the synthesizer unit. Pins D28, D30,
and D32 are used (in house) to program the synthesizer. Channel select lines CSEL 0 (least
significant bit) through CSEL 3 (most significant bit), which are available at pins D20, D22, D24,
and D26, are used once the synthesizer is programmed to select one of 16 channels. If the channel
select lines are all low (channel 0) the channel for the synthesizer is read from switches FSW1
(most significant), FSW2, FSW3, and FSW4 (least significant); otherwise one of 15 pre-
programmed frequencies is selected. Since the resulting frequency is dependent on the transmitter
model, refer to the section on frequency selection in the Transmitter Manual or to the channel
designation tables for that particular transmitter.