Ultra-Narrow Band Radio link - where to start?

sleeper1987 said:

"VERY clear"? - Sorry, I don't see how you get that impression . At worst, I figure what I've said could have made my intentions ambiguous. What did I say that made you think that?

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Wanting to use an illegal and unlicenced transmitter in the UK - how do you imagine that doesn't violate laws?.

Incidently, while we're talking low powers - years ago we had TV interference at work, wiping out TV reception over a couple of square miles. It turned out to be an unstable masthead amplifier - just one transistors, drawing a few milliamps, yet it had a massive effect.

Thanks for the info re the 27MHz legalities. When I was a kid my friend had some RC stuff from his planes and cars, we used to hook servos up to stuff in the backyard and try to spring mousetrap cages, set off firecrackers and other kids stuff.

Having no experience with RC hobbies etc I never would have guessed that was in violation of the rules.

We get a lot of rogue market traders who import illegal stuff...'toys from China' that are mainly R/C model aircraft that are running on 40MHz...Quite illegal, of course the Trading Standards people have a field day rounding them up and impounding their wares...

So what was wrong with using the XBee 9x modules? They can do 10miles with the right antenna.

blueroomelectronics said:

So what was wrong with using the XBee 9x modules? They can do 10miles with the right antenna.

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If they can manage 10 miles, it sounds an excellent option.

**broken link removed**
**broken link removed**

• 868 MHz short range device (SRD) G3 band for Europe
• Software selectable transmit power
• 40 km RF LOS w/ dipole antennas
• 80 km RF LOS w/ high gain antennas (TX Power reduced)
• Simple to use peer-to-peer/point-to-mulitpoint topology
• 128-bit AES encryption

Very nice

But I suspect he's looking for something a lot cheaper?.

Thanks for the replies guys.
As for the XBee - I was really looking to design something, rather than buy it. I know it'd be a lot simpler, and probably cheaper, to buy a pre-built module, but I'm interested in learning how to do it myself.

@Nigel Goodwin
Can I just clarify this with you: would it be illegal for me to to construct any transmitter, even if it was otherwise in compliance with the regulations? So, for example: I couldn't duplicate an existing RC plane controller, as I'd need to get it checked before using it?

If so, do you think it would be possible to reappropriate an existing piece of equipment, such as a walkie-talkie type radio, to circumvent that restriction?

Thanks again.

FRS walkie-talkies don't have that kind of range. You can legally (depending on your country) build a DIY transmitter without a license but it's power output will be very small.

If you're so interested in learning about RF transmitters why not join a local HAM club. They can help you get your license.

Legality is just a personal perspective. If your a law abiding person a few words from someone else is all it takes to prevent you from doing something.
However I prefer to just obey the laws of physics myself! They are self governing!

I have yet to have someone explain what classifies something as an RF transmitter Vs a device with incidental Rf emissions. If a multi milliwatt RF transmitter is illegal how can millions upon millions of devices give off countless watts of Rf energy in a broad spectrum legally?

As I have stated a few times before in other threads I do not have any RF transmitters that I operate to any great degree legal or other wise. BUT I do have a 30KW " broad spectrum RF hash generator" I run for hours a day at times with absolutely no concerns what so ever of being reprimanded for it!

Its my 105 amp plasma cutter and it uses a HF switching power supply too!
When my friends are using it I have seen it mess up every TV in my house even with all of my TV signals being feed through coaxial cable coming from a shielded satellite receiver! I suspect that there is a load of RF pouring out of it in order to grossly interfere with shielded coaxial wiring 100+ feet away! My nearest neighbor has commented on being able to pick it up nearly 1200 feet away on his AM radios too when I am out in the yard cutting up scrap iron with it!

If you build an Rf transmitter circuit its illegal, but what if you build an "LED flasher" circuit that just happens to give off an "unknown to you" Rf tone that just happens to be in the frequency your sending the purposed Rf dits on? (wink wink nudge nudge )

Laws and their interpretation are a very big Grey area!

Go nuts with your milliwatt dit n' dotter! I promise I wont tell anyone!

sleeper1987 said:

@Nigel Goodwin
Can I just clarify this with you: would it be illegal for me to to construct any transmitter, even if it was otherwise in compliance with the regulations? So, for example: I couldn't duplicate an existing RC plane controller, as I'd need to get it checked before using it?

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Certainly in the past (distant past!) you were free to build your own 27MHz radio control transmitters - but that was back when you had to pay a yearly licence to use them. In any case, using the radio control band isn't an option, as you're not allowed to use it for other than radio controlled models.

Licence free modules are available, mostly on UHF - but part of been 'licence free' means they have to have passed type approval, which isn't an option for a home made device (unless you are far richer than most here).

If so, do you think it would be possible to reappropriate an existing piece of equipment, such as a walkie-talkie type radio, to circumvent that restriction?

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Again you can't use a walkie talkie for data transfer, it's not covered by the licence, or licence free, conditions.

What EXACTLY are you trying to do, and over what terrain?.