3. Once the emergency voice call ends, the radio switches to the Emergency Revert's GPS
Revert Channel, f4, and transmits the Emergency Location Update.
4. After this transmission, the radio switches to the Emergency Revert Channel, f3, and while not
being involved in voice calls, it registers. (Note: This requires the Emergency Revert Channel
to be ARS enabled.)
5. After registration, periodic location updates are sent on the Emergency Revert's GPS Revert
Channel, f4, until the emergency is cleared.
This configuration in Figure 4-29 is useful when a system needs to simultaneously support multiple
Emergency Calls from multiple groups on a single Emergency Revert Channel. The placement of
Emergency Calls on the Emergency Revert Channel and the location updates on a different
channel significantly increases both emergency voice throughput and Location Update throughput
while in the emergency state. It should be noted that changing the Emergency's GPS
Transmission Channel to either the Selected Channel, f1, or the Emergency Revert Channel, f3,
removes one control station from the system. The actual configuration selected depends on actual
Channel Access Configuration
Channel access methods must be specified in the radio's codeplug for each channel via the CPS,
that is the TX (Transmit) parameters for each defined channel contains an Admit Criteria option
that must be set to one of the 3 possible values described below.
Channel Free, or
Color Code Free.
An Admit Criteria of Always is sometimes referred to as "impolite channel access". An Admit
Criteria of Channel Free is referred to as "polite to all". Finally, an Admit Criteria of Color Code
Free is referred to as "Polite to own color code". In polite mode, the radio will not transmit on a
channel if there is any activity detected on that channel. In impolite mode, the radio will transmit on
a channel regardless of any activity on that channel. When operating in impolite mode a radio user
will cause RF contention if there is another call on the same slot currently in progress. See
"MOTOTRBO Channel Access" on page 20.
Radio users provisioned for polite operation need only press their PTT to determine if they can
transmit or not. A Talk Permit Tone or Talk Denial Tone indicates if they have been granted or
denied access. Impolite users are allowed to transmit regardless if the channel is busy or idle,
although they would still need to wake the repeater.
It is important to note that the LED busy indication on the radios represents the presence of RF
activity on the selected channel and is not specific to the digital slot currently being monitored.
Therefore, if the LED indicates no RF activity on the channel, the radio user can be sure their slot
is idle. However, if the LED indicates the presence of RF activity on the channel, the radio user will
not know if their slot is actually idle or busy. If the radio users transmit when the LED indicates a
busy channel, there is a chance their transmission will collide with another transmission. Care
should be taken since RF collisions in digital mode most likely results in both transmissions not
reaching their intended target. Therefore, it is highly recommend that only well trained and
disciplined radio users are configured to have impolite channel access.
System Design Considerations