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307
| | Posted on Friday, November 30, 2001 - 9:40 pm: | 
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What's the "OFFSET" button on my radio for?
If you are one of the many owners of a radio that has a programmable offset built into the radio and are curious what it means then this may be for you . Offset is the terminology for a programmed frequency shift that when the microphone is pressed the transmit frequency goes to different frequency other than the receive . This frequency shift is needed to access local repeaters in the area . A repeater is a radio system normally located high up on a building or tower that has a very good coverage area or better known as foot-print . The input and output frequencies are different . Normally this difference is either 600 Kilohertz or 5 Megahertz . A repeater takes the incoming signal and routes it to a transmitter on another frequency and then re-transmits it . The benefit of a repeater is that from a mobile radio you may talk several hundred miles and not have to rely on skip waves .
Lets say you are in a mobile and you are in down town Orlando . If the repeater was on the 10 meter band , the frequency may be 29.600 megahertz output with 28.600 megahertz input . So you would set your 10 meter radio to transmit on 28.600 megahertz and receive on 29.600 . When you key your microphone and speak you would really be transmitting down 1 megahertz . The repeater would pick you up on that frequency and re-transmit you at a higher power level at 29.600 megahertz. This would give you a larger coverage area than the radio itself could put out . The offset button or program will let you set the desired offset that you need to get into these repeaters . The reason that the transmit and receive frequencies have to be different is because as the receiver in the repeater picks you up it can not re-transmit you on the same frequency there-for it re-transmits it on another frequency so the party you are speaking to can hear you at the same time . Because of this you must have the offset capability on your radio .
There are hundreds of repeaters in all cities in and around you . If you listen on a scanner you will notice that you always hear the people clear and clean . For an example , if you take the frequency of the local police department and subtract or add 5 Megahertz to it and reload that into your scanner you will not hear the repeater but you will actually hear the vehicle (person) talking into the repeater . The great thing about repeaters is that you may be 100 miles from a person that you want to communicate with but are unable to reach them because of the distance between you but if there was a repeater in-between then you could have reliable communications all the time . |
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