Tait T830 Series, Руководство по обслуживанию

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31/01/96 Copyright TEL
3.8 Audio Processor
3.8.1 Two Point Modulation
The T836 and T837 utilise two point modulation to obtain a wide audio bandwidth
independent of the synthesiser loop filter response. This is achieved by simultaneously
frequency modulating the VCO and phase modulating the synthesiser reference fre-
quency. The relative signal levels fed to the two modulators are quite critical and cause
interaction when setting up.
Both modulating signals require readjustment when the exciter is shifted in frequency
greater than the switching range (i.e.
∆
F>±4MHz).
Note: In this and following sections deviation settings are given first for wide
band sets, followed by settings in brackets for narrow band sets [ ].
3.8.2 Modulator Adjustment
1. Inject an audio signal of 600Hz 1.5V rms (+5dBm) into the CTCSS input (D-range
pin 8).
Earth the key line.
2. Adjust the output from the audio generator to obtain ±3kHz [±1.5kHz] deviation
at 600Hz.
3. Change the input frequency to 120Hz and adjust RV105 (ref. mod.) to obtain
±3kHz [±1.5kHz] deviation.
4. Change the input frequency back to 600Hz.
Repeat steps 2 and 3 above until the deviations achieved at the two input frequen-
cies are within 0.2dB of each other. This will need to be done at least four times.
5. Sweep the audio between 50 and 300Hz for peaks.
Note: A peak between 50 and 300Hz will indicate a fault condition, i.e:
- incorrectly set-up
or - modulation circuitry fault.
The specification window is ±1dB relative to 150Hz from 65 to 260Hz.
3.8.3 Limiter Adjustment
Set the audio processor links as appropriate for the required audio configuration
(refer to Section 3.3).
Inject 1kHz at -10dBm into the line input (D-range pins 1 & 4; pins 2 & 3 shorted
and 6 & 7 shorted; refer to Section 1.2 of Part F).