Site Trunking for the User in the Field

It is important to understand that all radios must be affiliated with a site in order to operate.  Further, the radio will only be affiliated with one site at any given time.  All radios operating on the system, whether Motorola or EF Johnson, are designed to seek out sites that are in Wide Area over sites that are in Site Trunking.  Therefore, if a field radio can find a site that is operating in Wide Area it will migrate to and affiliate with that site and abandon its affiliation with the site that is in Site Trunking.

Radios that are affiliated with a site that goes into Site Trunking may receive a visual indication on the radio screen (if so equipped) and may hear a periodic audible indicator (if the alarm is turned on in the radio).  When the radio finds and affiliates with a Wide Area site, both indications will go away and normal indicators will be indicated.  These indicators are the same for both field radios and radios utilized in a dispatch center or linked to an RF console.  These indicators are fed to the radio by the site that the radio is affiliated with at the time even though that site may not be currently connected to the system.

There will be occasions in which certain radios will not be able to find and affiliate with a Wide Area site and thus will remain affiliated with the site that is in Site Trunking.  This inability to find a Wide Area site may be due to the user’s location (such as low terrain or inside a building).  Thus, the user will probably be able to communicate with other users that are in their same area and conditions but may not be able to communicate with the dispatcher who may be affiliated with another site.  In fact, it could be that the dispatcher (with an RF console) may actually be the one who is affiliated with the site that is in Site Trunking and the field units may be affiliated with Wide Area sites.  Either situation presents opportunities for confusion, misunderstanding and desperation unless all are trained about Site Trunking and a “fall back” communication plan is in place and practiced.