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Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
Can anyone explain to me just what the FCC's designated frequencies mean? I realize that the spectrum is divided by usage, so CB gets some freqs, and RC toys get some, etc.
What I'm wondering is, would it technically be illegal to use, for example, the CB or FRS bands to send data instead of voice? I'm considering making a simple data transmitter attachment for my cheapie motorola FRS walkie talkies. I wouldn't change any of the hardware, i'd just encode my data as an audio signal...
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
I am not sure about the FCC rules but in most countries there are rules against anything interesting you can do with walkie talkies. Usually they must be manually operated so no automatic transmission and the data transferred must be voice, no encryption, digital or data transmissions.
I have managed to transmit using pure software on a PIC. By modulating 12 MHz from the crystal I could recieve the harmonics at 96 MHz clearly. I have not tried it at distances longer than 5 meters or with a proper reciever so I don't know what range to expect.
Registered Member #286
Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399
It is illegal to transmit data on the FRS frequencies unless the FRS unit comes with text messaging feature built in it. If you still want to transmit data. You can make your own transmitter under part 15 rules or get a ham license.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
You can get cell phone modules for about $70 that supports GPRS and all other standards. Then you can transfer the data over the internet in a fairly simple way. $1500 will get a satellite phone with a 9600 baud RS-232 internet connection.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
The only problem with a cellular modem is you have to pay for minutes (or data if you are dialing into the cell provider). You might consider maxstream, they have modules of all sizes and prices, most of which have transparent serial connections on them...
As to transmitting data over a walki talki, sure it is (probably) illegal, but I very seriously doubt that anyone will track you down... I wonder if you used morse code for the data....
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
In the US, the FCC spectrum definitions generally provide bandwidth, authorized users, and sometimes authorized modes. They generally aren't especially specific (though they're extremely specific in certain instances) regarding specific data transmission modes by name, but they often do specify maximum bandwidths, and other variables that limit the possibilities. On CB, FRS, GMRS, and a small ham allocation on 5Mhz only voice is permitted. On the 10Mhz ham band, only digital modes are permitted.
There are specific frequencies on which data transmission is permitted. 433Mhz, 27.110Mhz, 49.86Mhz and several in 900Mhz and 2.4Ghz are allocated for unlicensed data and voice transmitters utilizing extremely limited power.
As for the amateur bands, each allocated band is divided currently by mode. Generally the lower half of the band for digital only, the upper half for voice and digital. In the next 2 years the FCC is likely to adopt regulation by bandwidth instead, playing all modes less than 1Khz wide in the lower half, (this would keep SSTV, AM, SSB, FM and other voice modes off the lower half) and everything else in the upper half.
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