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Old 28th December 2010, 05:58 PM   #1
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Default Radio repeater kit?

A friend asked me to find out if there is a radio (walkie-talkie) repeater that is inexpensive. The commercial one he found is $3000!

He has an electronics background so he can assemble a kit.
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Old 28th December 2010, 10:54 PM   #2
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What frequency? You can make a repeater with a mobile radio and some other parts.

I assume you are licensed to transmit.
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Old 28th December 2010, 11:13 PM   #3
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About the time that US TV stations went all digital, the frequency assignments for wireless mics, walkie-talkie and such changed. So most older units are on borrowed time.
Short range walkie-talkie units didn't require licensing.
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Old 3rd January 2011, 12:02 PM   #4
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My buddy finally replied. He said that it is a GMRS radio operating around 462 Mhz.
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Old 4th January 2011, 03:02 AM   #5
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Technically any device operating in the UHF public safety spectrum where the GMRS frequencies lie must be "type accepted" by the FCC. This means that the manufacturer must provide test date, design information, and a full disclosure package to the FCC, pay the fee, and wait for an approval number before the device can be legally sold. Anyone caught selling non approved devices can be subject to all sorts of ugly stuff. This makes the possibility of finding a low cost unit for sale in the US unlikely.

Incidentally for a repeater device to work the hand held radio must transmit and receive on different frequencies. The repeater must also transmit and receive on different frequencies. The frequency pairs must be opposite from the repeater and the hand held unit, AND they must be seperated by enough spectrum to avoid interference in the repeater itself. The frequency seperation is traditionally 5.0 MHz in the UHF spectrum.

EXAMPLE:

The hand held units transmit on 467MHz, they receive on 462 MHz. THe repeater unit transmits on 462 MHZ and receives on 467 MHZ. The repeater is always listening on 467 MHz. If it hears a transmission from a hand held on 467 MHz the transmitter turns on and rebroadcasts what it hears on 462 MHz. All hand held units will be able to hear this transmission. Note that the repeater must transmit and receive at the same time. This is why the frequency seperation is needed. I have succesfully built repeater units by hacking old radios, but this is a hit or mis exercize with low probability of success.

The GMRS frequenies used to be called the Class A Citizens Band. There were frequencies allocated for repeater use. I am not sure that this is the case any more.
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Old 4th January 2011, 02:50 PM   #6
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Are there any restrictions on someone building a device to accomplish this?
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Old 4th January 2011, 11:04 PM   #7
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Quote:
Are there any restrictions on someone building a device to accomplish this?
Technically, yes. The device still will not be type approved. In reality if the device meets ALL of the technical requirements, meaning it does not emit unwanted frequencies (harmonics and spurious emission) and causes no interference to other users no one will ever know. At least here the FCC can't even stop the blatant pirate FM radio stations so a clean transmitter that causes no interference should go unnoticed. The GMRS frequencies are intermingled with the UHF public safety frequencies. A faulty transmitter could easilly cause interference with police, fire, and ambulance services which WILL get noticed, because most of those groups have technicians experienced in finding interference. Verifying a clean transmitter requires at least a spectrum analyzer. They don't come cheap.

About the only place where you can legally build your own transmitting equipment is in the ham radio frequency bands. This requires a ham radio license which has become extremely easy to get. Even there if you make a transmitting device for your own personal use, it's OK. Start selling them and the FCC wants type acceptance.
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Old 5th January 2011, 12:03 AM   #8
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Radio Shack used to sell little 'repeaters' that you could use on FRS and whatnot (same freq range,slightly different rules)..They had a delay built in,so that they would be compliant with the FRS rules..Radio #1 would receive the signal/audio,and save it..it would then wait a second or two,and re-transmit it on radio #2.

Last I knew they were going on Ebay for like $40,but that was a while ago. Might be worth keeping an eye out for one.
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Old 5th January 2011, 12:26 AM   #9
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Ham repeaters generally have an access mechanism such as a (CTCSS) tone or in the case of SSTV the vertical synch signal. An open repeater that simply rebroadcasts everything it receives is perhaps ill-considered.

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