User's Manual

If a portable's signal without PL tone is present when the repeater is interrupted, the
repeater transmitter remains inhibited for the duration of the incoming signal. If the
portable's signal is modulated with a PL signal, the priority unit repeats the message back
to the base station on top of the incoming signal.
In addition to giving the portable user priority over all incoming signals, the Portable
Priority Interrupt is used for three basic functions:
1. Self-Clearing - This is used when two or more priority VRS units are on the same
scene. On the first base-to-portable transmission, all priority VRS units will start to
transmit. The first one to have an interrupt and detect carrier without proper portable PL
(meaning another VRS is transmitting) will count up to priority state one, a condition
which is referred to as self clearing. This will continue to happen until only one priority
VRS is on scene.
As an example, consider a case in which both units A and B are in the priority
state (delay state zero). When conditions for repeater transmitting begin (i.e., the mobile
receives a base signal), both VRS units begin transmitting. Figure 13 shows the unit B
interrupt pulse occurring first (due to the random time factor added to the interrupt
interval). When unit B is interrupted, it detects another VRS unit transmitting and so unit
B's transmitter remains inhibited. Unit B is set to delay state one and unit A remains the
priority unit since by the time unit A's transmitter is interrupted, unit B is no longer
transmitting.
Figure 13 Self-Clearing Timing Diagram
2. Repeater Hangtime - This allows the user to get back into a conventional repeater
or trunked system during hangtime. The timing is faster for trunked systems due to the
added feature of talk permit tones being passed to the portable. If the portable keys up
with proper PL, then the VRS will key up the mobile. If proper PL is not sent, the VRS
will assume another VRS is in the area and count itself out of priority.
NOTE: If Repeater PPI is disabled on an analog trunking system with
transmission trunking enabled, the Quick Key feature becomes useless, since the user will
be unable to break-in during the repeater hangtime after the channel is acquired. For this
reason, repeater PPI should always be ENABLED on an analog trunking system.
3. Emergency - This allows the portable to have priority over dispatch.
A drawback of portable priority interrupt is that during all base-to-portable
transmissions, the signal drops out for approximately 6-8 ms every: 2 seconds
(conventional); or 1 second (trunking) if the "slow" PPI option is chosen; or every 500
ms (either trunking or conventional if the "fast" option is chosen in CPS).
The repeater PPI function may be used by the portable user in the following
manner:
During a base-to-portable transmission, the portable user wants to interrupt and
transmit to the base.
o Portable must transmit with the VRS correct access or steering PL.
o When the VRS transmitter is interrupted, the VRS will detect channel activity
from the portable's transmission and switch to receive mode.
o The VRS will then transmit VRS TX Audio to the base.
o The VRS RX Audio is routed to the mobile speaker.