BCT15X Conventional vs Trunked Systems Explained

Summary: The two kinds of radio system your BCT15X can monitor, how a trunked system works, and how the scanner’s Systems, Sites, Groups and Channels fit together.

Conventional Systems

In a conventional system each group of users has its own frequency (or a pair of frequencies for a repeater). Everything from that group always goes out on the same channel, so when the scanner stops on a frequency you generally know who you’re hearing and can follow a whole conversation. Aircraft, amateur radio, FRS/GMRS and small private radio users are typical examples. To program one you need a list of frequencies.

Trunked Systems

Trunked systems share a pool of frequencies between many groups of users. Three elements make them work:

• System controller – a computer that hands out voice channels as users key up.
• Voice frequency pool – the frequencies the controller can assign. Because they’re assigned only when needed, a 20-frequency system can support hundreds of channels.
• Talk Group IDs (TGIDs) – the user’s “channel”. Because voice frequencies are reused constantly, the TGID is how you tell who is talking.

A typical call runs like this: a user presses their PTT; their radio asks the controller for a channel on their talk group; the controller finds a free voice frequency and broadcasts a channel grant so every radio on the system knows where to listen; the call happens; and when the user releases PTT the frequency goes back into the pool. The whole set-up takes around half a second. The scanner listens to the system’s control channel to learn these grants, then jumps to the voice frequency for the talk groups you want.

The BCT15X follows Motorola, EDACS and LTR trunked systems. Note that the BCT15X cannot decode EDACS ProVoice, and it does not decode P25 digital voice (P25 support is on other Uniden models). A Motorola system with some P25 voice channels is still programmed as a Motorola system.

How the Scanner Organises Things

• System – the top level. You choose its type when you create it (Conventional, MOT, EDCS or LT) and can’t change the type afterwards. To change it, delete the system and recreate it.
• Site – trunked systems only. A site is one group of frequencies (typically one tower) within the system. Up to 256 per system.
• Group – a set of channels within a system, up to 20 per system. Groups are a convenient way to separate agencies or departments, and each can have a Group Quick Key.
• Channel – a frequency in a conventional system, or a Talk Group ID in a trunked system.

The next two articles walk through creating each type: BCT15X Programming a Conventional System and BCT15X Programming a Trunked System (Motorola, EDACS & LTR).

Scanning vs Searching Trunked Systems

For trunked systems the scanner combines both styles, depending on each system’s ID Scan/Search setting:

• ID Scan – only the unlocked Talk Group IDs you’ve programmed are checked. If one becomes active the scanner goes to the voice channel and stays until the call ends or the Delay Time expires.
• ID Search – any Talk Group ID that becomes active is checked against your lockouts, and unlocked ones are followed. The scanner monitors the system until the Hold Time expires and then moves on.

You can toggle a trunked system between ID Scan and ID Search while scanning with FUNCTION + tap SCAN.

Where to Find System Details

The manual recommends looking up frequencies, talk groups and site details in the RadioReference database, and using planning worksheets before you start. Programming from a worksheet saves a lot of time on complex systems.