The ABC's of Repeater Communications
If you've ever used a portable radio to communicate with others within the same building or within several city blocks, you've probably noticed that as you move further away, noise begins to mask the other person's signal until it completely disappears or becomes unintelligible. This is generally caused by two factors: obstructions, and the increasing distance between the two radios. One is quickly brought to a simple conclusion - that the most reliable communications are achieved when you and your partner are within "line of sight" - that is, when both radios can "see" each other. In practice, line-of-sight can range from several city blocks to many miles (such as in aircraft-to-ground communications).
What can be done to overcome these problems? An intermediate relay station between you and your partner would be immensely helpful. Such a station, called a repeater, picks up a transmitted signal on one frequency and immediately retransmits it on another. Your radio must transmit on repeater's input (or listening frequency), and then listen on the repeater's output frequency. For maximum effectiveness, most repeaters are located high above the ground - because the higher the antenna, the better. When the antenna is located higher above terrain, it can hear your portable or mobile radio much better, and the re-transmitted signal is beamed over a wider area. Two or more radios, many miles apart and separated by tall buildings or even mountains, can be linked together for reliable, clear communications if there is repeater strategically placed between them.
In order to serve the needs of multiple independent users, repeaters now use advanced trunking technology. Trunking is a 'time-sharing' method that allows a large number of repeater users to very efficiently utilize a limited number of repeater channels. It is similar to what the telephone company does when it routes one's interstate or international call - the customer gets the connection and couldn't care less which line (i.e. trunk) was used to connect him. When one wants to talk to another party through a trunking radio repeater, he presses the push-to-talk button on the radio, and the repeater controller is prompted to automatically search for an available channel. When it finds one, it grabs it and beeps the user that the channel is available. If no channels are available, one gets a busy signal just as on the telephone (another channel normally becomes available in a few seconds). The entire process takes just an instance and is completely transparent to the end user.
There are special features which can be programmed into a radio to adapt it to the specific requirements of your business. For instance, the radio can be restricted to calls among a special group of radio users, such as employees on specific assignment or duty. A radio user in such group will be completely oblivious to all other activity on the repeater, and other repeater users outside of the group will be equally oblivious to him, assuring a level privacy of business communications. This is just one of many ways that radio can be tailored to fit your needs.
See also: Radios, Base, Repeaters, Telephone Interconnects and Controllers
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