User's Manual

If unit B activates its VRS during portable transmissions, unit B does NOT transmit
Single Tone or enable in delay state zero. Unit B must wait until it cannot detect the
portable signal before transmitting Singletone and taking over as the priority unit as
described above.
Three-Unit Operation
Should another VRS-equipped vehicle (unit C) come into the area, the same sequence of
events occurs as previously described in the "Two-Unit Operation" section on page 21.
Unit C's arrival has no effect on unit A's or B's radio operation until unit C's VRS is
enabled.
Unless there are portable transmissions occurring when unit C arrives, unit C's repeater
transmits a Single Tone burst when its VRS option is turned on. Unit C's repeater priority
counter initializes in delay state zero, making unit C the priority unit. Unit A's
repeater/portable receives unit C's transmission which sets unit A's repeater to delay state
two. Unit B's repeater/portable receives unit C's transmission which sets unit B's repeater
to delay state one. Transmissions from portable units in the area now repeat through unit
C. All lower-priority units will receive incoming portable transmissions, but will not key
up their mobiles because they are in a delay state. See Figure 10.
Figure 10 Three VRS Unit Transmission Sequence
Departure of a VRS Unit
The priority unit may change, depending upon the order in which they leave, as vehicles
leave the coverage area. For example, in Figure 10, when unit A turns the VRS option
off, it has no effect on the priority unit (unit C). Unit C continues to be the priority unit
and repeat transmissions.
When the priority unit (unit C) turns the VRS option off and conditions for repeater
transmissions occur, the unit in delay state one (unit B in Figure 10) counts down to delay
state zero and becomes the priority unit. See Figure 11.
IMPORTANT NOTE: Non-priority units (those in delay state 1 or
higher) will not count down into priority if the portable user attempts to send a status or
message. If there is no priority unit on scene, the request will be ignored.
Figure 11 Priority Unit Reassignment
Rptr PPI - Portable Priority Interrupt
<Rptr PPI> is CPS programmable. The main function of <Rptr PPI> is to allow the
portable to interrupt base-to-portable transmissions. During VRS to portable
transmissions, an interrupt is sent to the transmitter every 2 seconds on conventional
modes and 1 second on trunking modes. (These times are CPS programmable and may be
changed to 500 ms for trunked modes or 500 ms for conventional modes.) There is also a
random time factor added to the base interval to prevent two VRS units from interrupting
at the same time. This interrupt allows the receiver to monitor portable or other VRS
activity for approximately 6 ms. See the timing chart in Figure 12.
Figure 12 Portable Priority Interrupt