E F Johnson Company 2425M70 Benutzerhandbuch

6-12

Either a single or dual priority channels can be programmed if desired. With dual priority, 
a call on the second priority channel is interrupted by a call on the first priority channel but 
not vice versa. When scanning and the selected channel is a single or first priority channel, 
“P” is indicated in the left status display next to the zone number as follows: 

This indication is displayed regardless of whether the priority channel is fixed or always 
the selected channel. When the second priority channel is displayed, “2” is indicated 
instead.

The priority channel sampling frequency is determined by the programmed Priority 
Lookback Time A (see description which follows). For example, if 2.0 seconds is 
programmed, the priority channel is sampled every 2.0 seconds when listening to a 
message on a non-priority channel. When not listening to a message, the priority channels 
are scanned in the normal scan sequence. With dual priority, the first and second priority 
channels are alternately sampled at the Loopback Time.

Priority channel sampling occurs only with conventional scanning. It does not occur with 
radio-wide scanning, when listening to any type of SMARTNET/SmartZone/P25 trunked 
call, encrypted call, or when transmitting.

The priority sampling times are programmed by the following parameters:

Lookback Time A - This time determines how often the priority channel is checked for 
activity. Times of 0.25-4.00 seconds in 0.25-second steps can be programmed.

Lookback Time B - This time determines how often the priority channel is checked 
once an incorrect Call Guard (CTCSS/DCS) or NAC code is detected. Since it takes 
much longer to detect an incorrect Call Guard signal than a carrier, this time should be 
relatively long to prevent the interruptions from making a message difficult to 
understand. Times of 0.5-8.0 seconds can be programmed in 0.5-second steps.

If a fixed priority channel is associated with the current scan list, it can be changed to 
another channel if the Priority option switch is programmed (or by menu selection). With 
dual priority, this changes only the first priority channel. To change both priority channels, 
use the Scan List Edit function described in Section 5.13.1. Proceed as follows to change a 
priority channel using the Priority option switch:

Priority Indicator