Motorola VRS750, Service Manual

Page: 48 / 104

36
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.
• Portable must transmit with the VRS correct access or steering
PL.
• When the VRS transmitter is interrupted, the VRS will detect
channel activity from the portable’s transmission and switch
to receive mode.
• The VRS will then transmit VRS TX Audio to the base.
• The VRS RX Audio is routed to the mobile speaker.
TX PL Self-Clearing
As part of the multi-unit resolution prioritization algorithm, TX PL
Self-Clearing operates by adding the VRS transmit PL to the list of PLs
that the VRS monitors. If a VRS transmit PL is detected by a priority
VRS (delay state 0), it will indicate that another VRS is transmitting.
This feature will cause the original priority VRS to count up to delay
state 1, 2, or 3, and allow the transmitting VRS to remain in priority.
The delay state is randomized to prevent multiple units from stacking
up in delay state 1. In order to prevent ICM transmissions from other
VRS units affecting the priority states, the TX PL Self-Clearing feature
only works when detecting TX PL from a VRS that is repeating a Base-
To-Portable transmission. This function is not programmable, but has
no effect unless TX PL is used. This feature will not operate properly
unless all VRS units are programmed to transmit with the same
frequency PL, and the receiver squelch of the VRS750 units is set to
approximately -110 dBm.
NOTE: The VRS750 ships from the factory with a receiver
squelch setting of approximately -110 dBm. If the
VRS750 is not going to be programmed with a TX PL,
then the Global Tuner can be used to loosen the
receiver squelch for better radio performance.