User's Manual

transmit or cause a mobile PTT. The procedures for determining priority levels in multi-
VRS operation are discussed next.
Determining Priority Levels
Whenever a VRS is enabled, it transmits a Single Tone burst (except if portable activity
is already present). The Single Tone burst frequency is fixed at 847.5 Hz. By default,
when a VRS (VRS number 1) unit is enabled, it becomes the priority unit with a delay
state of zero. When a second VRS unit (VRS number 2) is enabled in the area, it will
transmit a Single Tone burst as described. Upon receiving this signal, VRS number 1 will
know that another VRS is active and change its priority to delay state one from delay
state zero. If a third VRS were to be enabled, VRS number 1 would change to delay state
two and VRS number 2 would change to delay state one. This process could continue up
until delay state seven is reached by VRS number 1, meaning that eight VRS units have
been enabled. After eight VRS units are activated, they begin to stack up at delay state
seven.
Portable-to-Base Transmissions
If a portable begins to transmit, only the highest priority VRS will PTT its corresponding
mobile for transmission to the base. The other VRS units, however, will be able to hear
the portable transmission and monitor for mobile channel activity. Channel activity is
verified by a squelch detect of the mobile. For non-priority units, the portable's audio will
be sent to the mobile's speaker (unmuted) from the VRS, not from the mobile. This
allows the mobile to monitor the correct transmit frequency. If mode steering options are
enabled then the non-priority VRS units monitor their mobile's channel activity on the
channel steered to by the portable's PL and not on the mobile's current user selected
channel.
The non-priority VRS units have a short delay in which they expect to see the squelch
detect message. Conventional system units will wait at least 600 ms and trunking system
units will wait at least 1500 ms. This time period is referred to as one delay state. If in the
appropriate time frame a squelch detect message is not received, the priority VRS unit is
assumed to have been disabled and all other VRS units will increase one priority level
(for example, go from delay state 2 to delay state 1). The VRS units will continue to
count down until a squelch detect message is received. In an extreme case, in which all
but the lowest priority VRS units are disabled, it is possible that the remaining VRS unit
which was the lowest priority (highest delay state) will have to wait up to 7 delay states
before transmitting. This can lead to a transmission delay of up to 10.5 seconds for a
trunking unit.
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