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    To obtain Motorola software see the Sticky in the Motorola forum.

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Trunking explained

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Jun 18, 2005
Delaware County, PA
I’ll try a layman’s explanation for you as to what trunking is. But first, understand why.

Radio frequencies are a limited commodity, it’s very important to use them as efficiently as possible. When each agency within a service, (highway department, transit, police, fire, EMS, government), has their own frequency(s) there is a lot of waste. The amount of time a radio is actually “on-the-air” in a 24 hour period is remarkably short. There’s a lot of quiet time, but because the frequencies are licensed to specific agencies, others may not use them, so a sizable amount of radio spectrum is wasted in silence!

Using the efficiency of computers and the speed and accuracy of “data packets,” engineers designed a radio system that is very efficient, placing many, many agencies together on a limited number of frequencies. TRUNKING!

OK, so that’s the "why", here’s the "how":

It all lies in computer processors! A computer controller reaches out to each radio in the system. Each radio has a unique address (ID) that identifies it to the controller. The controller can assign the radio to “talk” on a frequency in the system that is not being used at that moment in time. Other radios in the system that should receive the communications are assigned to “listen” on that frequency. The controller determines who “listens” based on an address (fleetcode/talkgroup) unique to that group (fleet) of radios. For example, your local police department may be one fleet, and your local fire department might be another. When one of the radios in a certain fleet transmits, only other radios in the same fleet will hear that transmission. Depending on how many agencies are on the system at that moment, for greatest efficiency, the controller may assign a certain fleet of radios to different frequencies within a short amount of time. That’s why we need scanners that can follow the fleetcodes and thus hear the entire story. TRUNKTRACKING!

Now for programming a trunked system into your scanner:

Put the system frequencies in first. You probably have 10 “banks” of 100 “channels” (frequencies), or some other similar configuration. Select one “bank” and load the system frequencies into it in the correct order. (The correct order for most systems is given on this website.) Follow the instructions in you operator's manual.

You will notice one or more of the frequencies on the webpage are designated as “control” frequencies. This is where the computer is doing its work, communicating with all the radios in the system. If you listen to it in manual mode, you will hear that annoying, rasping hash sound. Those are the packets of digital information going back and forth between the computer and the individual radios. Believe it or not, it’s all 1s and 0s! Nasty sound though. If you program it properly, you shouldn't hear that noise when scanning. You may or may not need to perform an extra step to get your scanner to recognize the control channel, so make sure you carefully follow the instructions in your manual.

Next you may want to decide what groups (fleets) you want to listen to. Select the “fleetcodes” (listed on this website for most systems) and load them into the “bank” according to your operator’s manual. On most radios, once you have all the “fleetcodes” programmed, you can “lockout” any given group (fleet) you don’t want to listen to. This should all be covered in your manual.

Hope this helps!

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