User's Manual

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 23 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 7.
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.
Figure 7 Single VRS Unit Operation
Two-Unit Operation
The arrival of another VRS-equipped vehicle (unit B) into the coverage area of unit A has
no effect on unit A's radio operation until unit B's VRS is enabled.
Unless there are portable transmissions occurring when unit B arrives, unit B's repeater
transmits a Single Tone burst when its VRS option is turned on. Unit B's repeater priority
counter initializes in delay state zero, making unit B the priority unit. Unit A's
repeater/portable receives unit B's Single Tone transmission, which sets unit A's repeater
to delay state one. See Figure 8. Transmissions from portable units in the area now repeat
through unit B. See Figure 9.
Figure 8 Two-Unit VRS Operation
Figure 9 Two-Unit VRS Transmissions
A portable radio's transmissions (solid arrows in Figure 9) go to all portable radios and
VRSs in the area. Because unit B is the priority repeater, it repeats the portable's signal
(open arrows in Figure 9) to the base station and other mobile radios.
Unit A cannot countdown and repeat until the delay state one time delay elapses.
However, because unit A detects the mobile carrier of the priority unit (open arrow in
Figure 9) before the delay expires, the priority counter does not begin the countdown.
Unit A remains in delay state one and does not repeat portable transmissions.