Codan Radio Communications VT-3-150-SN User Manual
Transmitter Main Board Instruction Manual
3-7
4
Turn the transmitter on.
5
Adjust the balance compression level (R38) for compression at ±60% maximum
deviation.
deviation.
6
Set the audio frequency to 2.4 kHz, then adjust the deviation control (R29) for
maximum deviation.
maximum deviation.
7
Reset the modulating frequency to 1 kHz and re-adjust R38 for ±60% maximum
deviation.
deviation.
8
Repeat steps 6 and 7 until both conditions are met.
9
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 is
symmetrical. The variation between ± deviation levels should not exceed 300 Hz over
the 1 kHz to 3 kHz range.
then the negative deviation. Adjust the symmetry control (R14) until the ± deviation is
symmetrical. The variation between ± deviation levels should not exceed 300 Hz over
the 1 kHz to 3 kHz range.
10
Repeat steps 6 and 7 and re-adjust if necessary.
11
Adjust the balanced input level control (R31) until the deviation produced by a 1 kHz
tone at -8 dBm falls below ±60% maximum deviation, then adjust R31 so that the
deviation increases until compression is observed. The deviation should be ±1.5 kHz
or ±3 kHz for narrowband and wideband channels respectively.
tone at -8 dBm falls below ±60% maximum deviation, then adjust R31 so that the
deviation increases until compression is observed. The deviation should be ±1.5 kHz
or ±3 kHz for narrowband and wideband channels respectively.
12
A 1 kHz tone at -8 dBm input level should produce ±60% maximum deviation. If not,
go back to step 4 and make sure the pot is set for maximum gain and repeat the
procedure. If so, increasing the input level by +20 dBm should not increase the
deviation. This confirms that the AGC action of preamplifier U2 is working.
go back to step 4 and make sure the pot is set for maximum gain and repeat the
procedure. If so, increasing the input level by +20 dBm should not increase the
deviation. This confirms that the AGC action of preamplifier U2 is working.
13
A 2.4 kHz tone at the desired audio input level should produce the maximum
deviation. Increasing the input level by +20 dBm should not increase the deviation.
This confirms that the limiting action of U4a and U5a is working.
deviation. Increasing the input level by +20 dBm should not increase the deviation.
This confirms that the limiting action of U4a and U5a is working.
14
Set the audio frequency back to 1 kHz at -8 dBm output. Confirm and record audio
distortion with the appropriate filter on the communications test set.
distortion with the appropriate filter on the communications test set.
15
Confirm the audio frequency response by referencing all output deviation
measurements to a 1 kHz input tone at ±20% maximum deviation (±500 Hz for
narrowband or ±1 kHz for wideband).
measurements to a 1 kHz input tone at ±20% maximum deviation (±500 Hz for
narrowband or ±1 kHz for wideband).
16
Remove the signal to the balanced input (pins B18, Z18).