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Table Of Contents

3-10

Transmitter Main Board Instruction Manual

3.10

MT-3 Audio Processor Alignment (Version 1.8)

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text

3.10.1

General

Verify

the standard factory

settin

gs for the MT-3 Audio Processor as

given

in section 3.9.1 before

beginning the standard

deviation

adjustment

procedure. If the

transmitter's

channel

frequency

changes,

the audio processor should be

realigned

optimize

the

transmitter's

performance.

The

schematic

diagram

for the audio processor is shown in section 5.5.2 and the

component

layout is

shown in section 5.5.1.

3.10.2

MT-3 Audio Processor Standard Deviation Adjustment

Note:

clockwise

rotation

of controls increases signal

levels.

1 Connect the

transmitter

to the radio

communications

test set and

monitor

deviation,

distortion,

and audio frequency. Before

adjusting

the audio

deviation,

confirm that the

transmitter

RF output frequency is

correct.

2 Connect the 600 ohm input to the

incomin

g audio (pins

B18,

Z18). Set the audio

frequency to 1 kHz at the desired

level

of -8 dBm.

3 Increase the

balance

level

control (R31) so that the

deviation

increases

until

compression is

observed.

Adjust

the compression control pot (R38) for compression at

±60%

maximum

deviation.

5 Set the audio frequency to 2.4 kHz, then adjust the

deviation

control (R29) for

maximum

deviation.

6 Reset the

modulating

frequency to 1 kHz and re-adjust R38 for

±60%

maximum

deviation.

Repeat

steps 4 and 6

until

both conditions are met.

8 Vary the audio signal from 1 kHz to 3 kHz and measure the

positive

deviation

and

then the

negative

deviation.

Adjust

the symmetry control (R14)

until

the

deviation

symmetrical.

The

variation

between

deviation

levels

should not

exceed

300 Hz

over

the 1 kHz to 3 kHz range.

Repeat

steps 4 and 6 and re-adjust if necessary.