Raytheon SNV-12, Installation And Operation Manual

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SNV-12 Operations Manual
3-43
3.12.2.6 CIM Audio Level Adjustment
As shipped from the factory, the input and output levels of each Console Interface Module
(CIM) module are set to -10 dBm. If level requirements differ, the Console TX Audio Input
level may be adjusted via potentiometer R50, (available through an access hole in the front
panel on the CIM-2, and on the CIM-1 near the top center of the board). Similarly, the Voted
Audio Output can be adjusted using the Voted Output potentiometer (R67) located on the front
panel (CIM-2) and internally near the top center of the board (CIM-1).
Console TX Audio input is conditioned by the DSP circuitry on the CIM module before being
placed on a TX audio bus to be picked off by any site or sites chosen to transmit this audio.
DSP functions include detection of EIA keying tones, addition of EIA tones, and digital audio
delay. This input is set at the factory for -10 dBm average voice audio input. When Repeat
Mode is enabled, the retransmitted voted audio does not pass through the CIM‟s DSP, but the
DSP may be set to add keying tones to the voted audio as it is placed on the TX audio bus. To
keep the Console TX audio and the retransmitted voted audio (repeat audio) signals at the same
relative level, and to ensure that the DSP has sufficient headroom, it‟s important that the
Console TX Audio input be correctly set.
When the voter is set to detect EIA keying tones in the console transmit audio, the tones should
follow the EIA specification. The CIM detection algorithm is fairly forgiving, but if problems
with detection occur, first check the input level adjustment as described below and then work
with the console to bring the input key tones into alignment with the specification:
The High Guard (Alert) Tone should be 125 millisecond long at 2175 Hz, 10 dB above
average voice audio.
The Function Tone should be 40 msec long at the average voice level.
The Low Guard (Hold) Tone should be at 2175 Hz, 20 dB below the voice level.
Either of the two following methods may be used to set the input level in the CIM. Method 1 is
the preferred approach, but method two will give satisfactory results in most installations:
Method 1:
Using a tone box, generate a 1kHz tone into the console‟s microphone, at a level that
will produce 100% modulation. (Some consoles produce a test tone that can be used
during alignment.) The 1kHz test tone is used to simulate average voice.
With the test tone still generated, set the console‟s output to the appropriate system
level (normally -10dBm) for the connection medium that links it to the voter.
Continue to generate the test tone and adjust the Console Input pot (R50) on the CIM so
that the Norm LED just lights. Verify this adjustment by connecting a transmission test
set to test point 3 (TP3) and ground. Verify a level of approximately 0dBM for the CIM.
Method 2:
The CIM front panel PEAK and NORM LEDs may be used to easily set the Console TX Audio
input level without the need for any external equipment. When the Console TX Audio input
control is adjusted properly, the NORM LED on the module will be lit during typical speech,
and the PEAK LED will flash occasionally on peaks in speech input. If the NORM LED never
lights, or if the PEAK LED lights frequently, then the RX audio level into the CIM is not
correctly adjusted. Note that these LEDs assume a typical speaking voice at typical volume
levels. There is room for variation if some console operators speak more loudly than others.