FINDING THE NEEDLE IN AN ELECTRONIC HAYSTACK

Sometimes, though, we do not say exactly what we mean. 

Before surgery begins, we say we want the anesthesiologist to put us to sleep when what we really want is for the good doctor to wake us up afterward. We say we want a drill bit when what we want is a hole. When we talk about recording a trunked radio system, what we really want is to be able to hear what was said in a particular conversation. When it comes time to listen to a particular conversation especially if it had been a "private conversation, there may be a serious problem. After a trunked radio system has changed channels a few times, finding and playing back a particular conversation is more difficult than finding a needle in a haystack.

Recording (logging) a conventional two-way radio system is easy. An ordinary, multichannel (multitrack) recorder works fine. Finding and replaying a conversation requires only that you position the tape and play the correct channel.

Logging a trunked radio system is another matter. Figure 1 below shows communication activity on a typical, small, trunked system. Routine talk group transmissions, private transmissions and a telephone interconnect are color coded. Notice how the individual transmissions hop from one frequency to another. Transmissions move around for several reasons.

The frequency-hopping allows the system to find and open channel. Furthermore, it ensures a more even channel-loading.

Many trunking radio systems are equipped for telephone interconnects and private conversations. Logging a telephone interconnect conversation is not normally a problem because the recorder can be connected to the telephone lines that are dedicated to the system controller. Private calls, on the other hand, present a number of problems. Contrary to popular belief, a private call does not tie up a physical radio channel as a telephone interconnect does. Instead, a private conversation is, to the trunking radio system, an ad hoc talk group that is created on the spot for the two radios involved in the private call. There is no formal redefinition of the programmed system talk groups, and when the private call ends, the ad hoc talk group vanishes.

Previously, the only way to log and record a trunking radio system was to de-trunk the talk groups prior to recording and use a standard multichannel (multitrack) recorder. With this method, you need equipment to de-trunk each talk group, and private conversations are extremely difficult to record if you can record them at all.

There are several solutions:

1. Do not assign many talk groups. (Unfortunately, this would defeat the effectiveness of the trunking radio system.)
2. Do not allow private calls. (Unfortunately, this would limit management and supervisory effectiveness.)
3. Do not create new talk groups until you have the necessary equipment and recording channels to capture them.

These probably are not practical solutions.