Tait T850 II Series, Service Manual

Page: 167 / 370

M850-00
T856/857 Initial Tuning & Adjustment C3.13
Copyright TEL 31/09/98
Check that ±3kHz deviation (±2.4kHz) [±1.5kHz] is still available.
Slowly increase the audio input level until the demodulated waveform shows sig-
nificant signs of clipping (approximately ±4.5kHz (±3.6kHz) [±2.3kHz] deviation).
Adjust RV220 anticlockwise until the demodulated waveform is just clipping
(approximately ±4kHz (±3.2kHz) [±2kHz] deviation).
Increase the input level to -10dBm and check that the test tone is still held just into
clipping. The input line level should be typically -10 to -20dBm.
3.9.5.2 Compressor On Microphone Input Only
Key the transmitter by earthing the Tx-Key line and plug a microphone jack into
the front panel socket.
Adjust RV220 (compression level) fully clockwise.
Acoustically couple the microphone to a tone box (1kHz) and close the PTT
switch.
Increase the audio level until the demodulated waveform shows significant signs
of clipping (approximately ±4.5kHz (±3.6kHz) [±2.3kHz] deviation).
Adjust RV220 anticlockwise until the demodulated waveform is just clipping
(approximately ±4kHz (±3.2khz) [±2kHz] deviation).
Increase the audio level by 10dB and verify that the test tone is held just into clip-
ping.
Whistle steadily into the microphone, checking that approximately ±4kHz
(±3.2khz) [±2kHz] deviation is produced. The modulated waveform should be
basically sinusoidal.
Speak into the microphone, checking that the modulation peaks reach about
±5kHz (±4kHz) [±2.5kHz] deviation.
As the line is to be used without compression, set RV210 (line sensitivity) as
described in Section 3.9.4.
3.9.5.3 Compressor On Both Line & Microphone Inputs
Set up as described in Section 3.9.5.1.