Edacs Trunking

One big difference you will notice with digital versus analog transmissions, is that with analog systems, you might be able to hear weak signals interspersed with hissing. As you move further away from the system, the interference gradually increases until you are unable to make out the transmission. With digital systems, the cutoff point is much more abrupt. You might have a small area where partial decoding occurs...in which case you will hear partial and garbled audio. However, once the scanner is unable to receive the data well enough to decode it, the audio stops entirely. For the best range, antenna selection and placement is critical. See “Connecting an Antenna” for more information.

EDACS trunking works in much the same way as Motorola trunking with a couple of major differences. In an EDACS system, each frequency used by the system is assigned a Logical Channel Number (LCN) so that less data needs to be transmitted by the control channel. Also, talkgroups are assigned in an Agency-Fleet-Subfleet (AFS) hierarchy. Also, there is one variation of EDACS called SCAT that your BC796D can monitor.

•Logical Channel Numbers – each frequency used by the system is assigned an LCN. This information is programmed into each user radio. When a user presses PTT, their radio sends their AFS information to the control channel. The computer then assigns that talkgroup to a channel and sends the LCN so that all other radios in that talkgroup will switch to the correct channel. To program a EDACS system in your scanner, you will need to know both the frequencies used by the system and the LCN for each frequency so that you can program the frequencies in LCN order.

•Agency-Fleet-Subfleet– talkgroup ID’s for EDACS systems are assigned in a way that makes it easy to see at a glance the affiliation of the user. Each radio is assigned a 2-digit agency identifier from 00 – 15. For example, 01 might be used by the police, 02 by ambulance service, 03 by the fire department, and so on. Each agency is then subdivided up to 16 times to provide fleet identification, and then 8 more times to identify subfleets.

For example, the complete AFS for the Police Department West District’s dispatch channel might be 01-062. 01 identifies the agency as the police department, 06 identifies the fleet as the West district, and 02 identifies the subfleet as the dispatch channel. While these assignments are somewhat arbitrary and vary from system to system, there are many resources on the web for finding the assignments for most systems.

Because of the logical hierarchy of the AFS system, your BC796D lets you assign wildcard ID’s that let you, for example, use only one ID memory to identify all units in either an agency or a fleet.

•EDACS SCAT – EDACS SCAT (Single Channel Autonomous Trunking) systems operate on a single channel and alternate control data with analog voice traffic. While your BC796D cannot track ID’s in this system, it can eliminate the control data so that all you hear is the voice transmissions when you monitor this type of system.