Motorola VRS750, Service Manual

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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 24 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.
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.
Figure 24. Self-Clearing Timing Diagram
TWO UNITS IN PRIORITY STATE
MOBILE RADIOS A & B
RECEIVE MESSAGE
REPEATER A
TRANSMITS
REPEATER B
TRANSMITS
REPEATER A WAS NOT INTERRUPTED AND REMAINS
THE PRIORITY UNIT.
REPEATER B WAS INTERRUPTED BY ANOTHER REPEATER,
THEREFORE DELAY IS INCREMENTED BY ONE UNIT.
MAEPF-26085-O
INTERRUPT
PULSE
DELAY STATE
DELAY STATE
0 0
0 1