Instruction manual

ACU-1000 Operations Manual
Interoperability Now 4-5
4.3 Missed Syllables Mid-Conversation
The most likely causes of missed syllables in mid-conversation are VOX/VMR dropout or
COR sampling. If the VOX/VMR hangtime is incorrectly adjusted, the VOX/VMR will
momentarily unkey the transmitter and then quickly rekey. The solution is to increase the
hangtime to be slightly longer than the speech inter-word time. This is discussed in Section
2.17.2.6.
COR sampling requires that PTT be dropped for a period of time every so many seconds.
When PTT is dropped, there will be a hole in the audio. See Section 2.17.2.7 for a detailed
explanation of COR sampling. This problem might be recognized by a regular pattern of
interruptions on a long speech sample. Turning this function off temporarily would help
identify if it was the cause of the problem.
4.4 Stuck Channel
Consider again the basic concept of radio-to-radio cross-connections. When one of the radios
cabled to the ACU-1000 is unsquelched, all cross-connected system radios are transmitting.
To the system users, this means that if a single radio operator keys his radio, all other radios in
the cross-connected systems will be listening, and unable to access the system until the first
user unkeys.
Now consider what happens if an ACU-1000 system radio is inappropriately unsquelched and
stays unsquelched for an extended period. Possible causes are a problem with the radio,
interference on its frequency, or a radio in the field that’s stuck in the key-down mode, etc. It
could simply be someone who is terribly long-winded and won’t let the other system users
break in. Whatever the reason, any system radios cross-connected to the problem radio will be
stuck in the transmit mode, and the associated system users will not be able to access the
Interoperability System. Refer to Figure 4-3 and consider what happens to the system if the #4
portable fails to unkey.
This problem is also referred to as “stuck mic”.
The best solution is called “COR Sampling” (also referred to as “COR Sniffing”). With COR
Sampling, the COR inputs of other radios in the connection will be occasionally sampled, and
if one is active, it will be given control of the system. This provides an opportunity for another
user to break in and take over the control of the system. This may give that user a chance to
alert the system’s operator that there is a problem (if there is an operator monitoring ongoing
voice traffic), or if DTMF control is available, this user can disconnect his radio from the
system.
An effective COR Sampling function should have the ability to set how long any channel is
“Stuck” before the sampling begins. This is important because the “stuck channel’” radio must
be cut off momentarily for the function to operate, and it’s important that this does not happen
inappropriately.