SNV-12 Operations Manual
5-7
5.10.4
Audio Level COR with a Squelched Receiver
If a COR output signal is available from the receiver, either Hardwired COR or pilot tone
generators should be used. If it‟s impossible to attain a COR signal, the SNV-12 can use a
sensitive level-detecting algorithm to allow operation with squelched receivers. This mode will
not work well if there is a requirement for repeated voted audio and also may not function well
for some systems due to variations in noise levels. If the receive signal when unsquelched is
noisier than the squelched signal, the SNV-12 can use this increase in noise level as an
indication that the radio is unsquelched.
If there is not a detectable difference in noise between the squelched and unsquelched
condition, the SNV-12 can be set to indicate an unsquelched condition (COR active) whenever
speech is present. COR is maintained while the increase in signal level is present and for a
short Hangtime afterward. The receive audio signal level threshold is individually set on each
SVM by switches SW2-5 and 6. Note that it may be difficult to set these thresholds to function
correctly in a laboratory setting. The SNV-12 must detect the extra noise from the unsquelched
receiver, and keying a handheld transmitter in close proximity to the receiver in a lab may
result in a receiver that is so fully quieted that no detectable increase in noise occurs. A
communications service monitor should be used when setting these thresholds. Note also that
noisy lines may cause a site to become inappropriately unsquelched and voted. Because of
noisy lines and/or insufficient unsquelched radio noise, it may sometimes be impossible to
attain reliable performance using this COR method. If so, pilot tone generators must be added
(see Section 7).
NOTE: Audio Level COR must not be used in conjunction with Repeat
Mode. When Repeat Mode is selected, every time a site is voted, the
associated transmitter is keyed and retransmits the voted audio. When
Audio Level COR is selected, any type of noise burst or momentary
static on the receive audio lines to the voter will cause the associated
SVM to unsquelch and voting will occur. This will create an unwanted
transmission when in Repeat Mode. Since the threshold for detection of
COR is the low level of broadband noise present when the receiver
unsquelches, low-level noise or static will cause the voter to unsquelch
and vote. This is not normally objectionable in non-Repeat Mode.
However, the inadvertent keying of the transmitter that can result if
Repeat Mode is used with this COR type usually requires that pilot tone
generators be added.
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