TN180 P25 Digital Ping Feature
MT-4 Radio Systems
TECHNICAL NOTES
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TN180, REV 1-0-0, © Aug 2016
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A conventional radio system requires the users to set the subscriber radio on the frequency pair of the nearest
repeater by manually turning the channel selector knob. This requires more training and attention on the part of
the radio user.
Subscriber radios can be programmed to scan the repeater transmit frequencies to lock onto the repeater when it
is transmitting. Standard scanning results in the subscriber selecting and using the fi rst channel in the scan list it
fi nds an active (transmitted) signal. Since the repeater talk-out range is generally greater than the subscriber talk-
in range, standard scanning does not always result in the optimal channel (typically the closest repeater) for the
subscriber to operate on.
In Vote Scan operation, each channel is qualifi ed by measuring the received signal strength of each repeater at
the subscriber radio. The subscriber then votes from the repeater sites, selecting either the best signal or the fi rst
signal that exceeds a pre-programmed received level threshold.
In order to keep the subscriber locked onto the best (typically closest) repeater site when the subscriber is keyed,
the repeaters need to have traffi c on the transmitter regularly. Since the radio users may not have consistent radio
traffi c, a Codan repeater can be programmed to ping after an inactive time interval allowing the vote-scanning
subscriber radios to lock onto the best repeater. The ping uses the P25 standard “silent” message, so that users
will not hear the radio traffi c, but it will activate the vote-scan capability in the subscriber.
The optional digital ping software timer is confi gured to key the transmitter after a specifi ed time (interval) with no
activity, with a message of programmable duration (length) as shown in Figure 1.
Figure 1: Optional P25 Digital Ping Feature
Ping Interval range: 10 sec to 120 secs.
Ping Length: 1 sec to 15 secs (rounded to nearest LDU length – 180 mS)
The maximum Ping Length is less than 50% Ping Interval. e.g. Ping length < 5s if Ping interval set to 10s.
Setting the Ping Interval to a small value and the Ping Length to a large value will cause excessive network traffi c.
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