Raytheon SNV-12, Инструкция по установке и эксплуатации

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SNV-12 Operations Manual
3-73
3.12.6.5 SVM-2 Switch SW5 Settings
Note: There is no SW5 on the SVM-1 module. It was added when the
SVM-2 Module was designed. Some of the SW5 features are available on
the SVM-1 by shorting rear panel terminals to ground. This is explained
in the following sections.
NOTE- Factory settings are marked *.
SW5-1 Pilot Tone Regulated AGC
Each SVM can be set to run a DSP AGC algorithm to automatically adjust the levels of RX
audio receptions. This AGC is intended to compensate for level changes in the link between
each remote receiver site and the SNV-12. It is not intended to compensate the different
volume levels of different system users. The AGC tracks the level of the pilot tone input; if it
changes, the SVM‟s internal DSP gain is changed to compensate. This feature uses changes in
the incoming pilot tone level as an indication of changes in the overall incoming RX signal
level, which may result, for example, from gain changes in a microwave link. The AGC gain
setting varies only when pilot tone is present and "freezes" when the pilot tone disappears.
Thus, the gain applied to each individual transmission from a system user depends on the level
of the pilot tone that preceded it at the SVM‟s RX audio input.
Table 3-66 Pilot Tone AGC
SW5-1 AGC Feature
OFF Disabled *
ON Enabled
In order for the AGC system to produce the correct receiver audio level in the SVM, the pilot
tone must arrive at the SVM input in a known relationship to the receiver audio level (per the
set-up procedure that follows), and this relationship must remain constant over time. For
example, the AGC will perform well if the transmission medium between the receiver site and
the SVM has a constant frequency response characteristic, such as is found in a microwave
system. However, the AGC will not perform well if the transmission medium is a telephone
line whose high frequency response varies over time. The AGC would then track these high
frequency response changes even if the voice levels have not changed (since the pilot tone that
regulates the AGC is at a higher frequency).
If the frequency response at the pilot tone frequency changes, the AGC will produce a gain
error in the program audio. The system performance under these conditions will be much better
if the Pilot Tone Regulated AGC feature is not used.