Motorola VRS750, Service Manual

Page: 42 / 104

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On conventional modes if the VRS <Base Repeater> option is enabled
via CPS, then an additional 300 ms time delay is added to the delay
states. This allows time for the mobile radios to transmit to and receive
from a repeater site.
Base-to-Portable
Transmissions
When a base transmits, only the priority VRS unit will transmit to the
portable. The other VRS units monitor activity on the portable
channel. Similar to the previous case, if portable activity is not
detected in the specified time frame after receiving mobile channel
activity, the non-priority VRS units will decrease one delay state, until
eventually one unit is in priority.
During base-to-portable transmissions, the delay state timing is
slightly different from that encountered during portable-to-base
transmissions. On conventional modes, the first delay state is
1 second; on trunking modes, the first delay state is 3.4 seconds. All
other delay states, on either trunking or conventional modes, are
400 mS. The worst-case delay for a unit to count into priority during a
base-to-portable transmission in a trunking system would, therefore,
be 5.8 seconds.
See the description of the Portable Priority Interrupt feature on
page 34 for information on the self-clearing feature used to re-
establish a single priority unit when multiple units are mistakenly in
priority. This condition may occur when a VRS unit is activated before
arriving on a scene, or in the unlikely case where several units stack up
at delay state seven and all higher priority units (those in delay states
one through six) leave the scene first or are otherwise disabled.
Single Unit Operation
Normal radio communication between a VRS-equipped vehicle (unit
A) and the base is via the mobile radio. When the operator decides to
leave the vehicle and use the VRS option, simply press the VRS button
or remove the portable from the charger if VIP operation is enabled to
turn on the vehicle’s repeater. The repeater transmits the Single Tone
burst on the associated portable radio frequency and sets the delay
state to zero. When the delay state is zero, this unit is the priority unit.
See Figure 18.
IMPORTANT NOTE: The VRS is designed to be a stationary
repeater system. The VRS unit should
always be disabled when the vehicle is
moving. FAILURE TO DO SO COULD
RESULT IN ERRATIC SYSTEM
OPERATION.