Instruction manual

ACU-1000 Operations Manual
4-6 Interoperability Now
Another way to deal with a stuck channel is for a system operator to constantly monitor all
system activity and disconnect any offending radios. In practice, this is too much to ask of a
busy operator who most likely can only monitor each ongoing cross-connection for short time
periods.
4.5 Ping Pong
Some radios have a tendency to unsquelch momentarily at the end of each transmission.
Remember that for any pair of cross-connected radios, whenever one radio is unsquelched, the
other is keyed. If a radio in an Interoperability System exhibits the “momentary unsquelch”
behavior, any cross-connected radio will momentarily (and inappropriately) transmit. If both
radios unsquelch momentarily at the end of each transmission, the system will repeatedly
“ping-pong”, with first one radio keyed momentarily and then the other.
This effect can be experienced when the PTT inputs are activated by either a COR input or a by
VOX.
There are two ways to prevent this. First, turn on the adjustable “COR (unsquelch) Inhibit
Timer after PTT”. This function instructs the module to ignore any unsquelch detection (COR)
that occurs immediately following the cessation of a transmit sequence. The duration of the
timer is adjustable to optimize for different radios, which may exhibit the inappropriate
unsquelch indication for times as short as 100 milliseconds, and as long as several seconds.
Invoke the feature for each DSP-2 module that shows a short burst of COR just after a keying
sequence; this can best be seen by observing the DSP-2 module front panel LEDs.
Another way to prevent this is to use neither COR nor VOX, but instead use VMR. Since
Voice Modulation Recognition will not trip unless human speech is actually present, these
momentary (and inappropriate) unsquelch conditions will simply be ignored by the system.
4.6 False Keying
When a radio is installed in an environment with lots of RF emissions near the receiver’s
frequency, these emissions may cause the radio to unsquelch inappropriately. Some radios
have a greater tendency for this problem than others. When the inappropriate unsquelch
occurs, any radios cross-connected with the offending radio will momentarily transmit a loud
burst of noise.
If any radio has a tendency to key on noise (and it’s not possible to rectify by reducing the RFI
or altering antenna placement), the best solution is to change that radio’s system interface to
VMR Mode rather than to use either COR or VOX. In VMR Mode, the Interoperability
System will ignore these inappropriate noise bursts because the VMR will trip only when
human speech is detected in the receive signal.
Any incident scene is likely to be a volatile RF environment because of the wide range of
communications devices being deployed. This makes the “on-the-fly optimization” capability
of the ACU-1000 very beneficial. A quick switchover to VMR mode can easily be made by the
ACU Controller or WAIS Controller when changing conditions warrant it.