Type of Modulation Used in Walkie Talkie

Probably still NBFM.

Maybe, but that's unlikely to be legal. Check local regulations for the band of interest... or just buy a data transceiver. They're plentiful, cheap and legal. See for example

Some of the newer ones are UHF digitali, I believe. Not sure how common they are yet.

I am likewise uncertain about the llegality of continuous transmission, but one factor is a built-in time limiter once you press the talk button. I have seen retriggering circuits to circumvent this.

I wonder if anything in the unit would overheat. I do have a portable refrigerator.

Richard Clarke

Look into radio control as used by model enthusiasts, that's continuous data, but not full time.

the 27MHz HF ones were mostly AM, with some doing SSB also, I have not looked closely at the UHF ones, but as TVs could receive the signals I assume it was FM.

--
Neither the pheasant plucker, nor the pheasant plucker's son. 


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(Note this assumes you're a U.S. resident. Outside the U.S., the rules are different)

Cheepie FRS handhelds are NBFM -- remember, cost is king. FCC type acceptance requires an essentially sealed package and a fixed antenna. Piggybacked data? Garmin had to go through many interesting times to get FCC approval for their Rino handhelds that piggyback GPS location data with voice on FRS channels.

Some commercial stuff is digital, but those are expensive. Ham radio is starting to work more with digitally encoded voice, but FCC regs still make that work difficult.

And speaking of ham radio, if you are interested in experimenting with data transmission, the Technician Class ham radio license consists of

35 multiple-choice questions. You can pass this test after a one-day cram class, using short-term memory and common sense. 12 and 14 year olds regularly pass this test. (Discussions of this study methodology are best left for other forums).

Get your tech class license and you can explore these areas in the 50 MHz and above ham bands. Type acceptance? In the ham bands, not as much of an issue, particularly for experimental uses (yes, I know, much fine print applies).

And if you're looking to do specific kinds of telemetry, such as location and data from a balloon, hams have developed solutions to those problems, such as APRS, the automatic packet reporting system, which can be used to track and monitor weather, balloons, cars, and much other stuff.

APRS is based on packet radio. Low-speed packet radio still makes uses of voice-grade ham transceivers (usually in the 144 MHz band) and an external packet modem. More specialized data radios evolved that achieve higher data rates by designing for data, rather than voice.

Packet radio lets you send data from place to place. Protocols range from the very simple to AX.25, derived from X.25, and providing the data link layer as a building block (AX.25 is supported under Linux).

Have fun--

Probably this:

Not really. And it might not be permitted by FCC rules against modding FRS radios in certain ways (can't change antennas, etc.)

How far and at what rate do you need to t/r data? There are some ready made solutions you could adapt to your app. that may work.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com 
------------------------------------------------------------------ 
On a clear desk, you can sleep forever.

** Only if you don't give a hoot about the data getting through.

Or a hoot about the relevant law.

.... Phil

Oh, I don't think that is legal in the US, at least unlicensed. But good for a pirate FM station, even in Japan. I worry about cheap FM transmitters drifting into the nearby aviation band, but this one is PLL based.

If I were to do a data link, I'd do it in the 900MHZ ISM with a hopper. Many of the users are hopping and directional, so the shared band isn't as bad as one would think. There are ethernet backhaul systems in this band.