Hi!
I'm looking to design a single-directional radio link, for transmitting small amounts of data over a distance of about 10 miles. I don't want to obtain a licence to do so, so what means are available to me?

I've read about ultra-narrow band systems, which sound like a viable option, as I could use very low power transmissions. I'm currently a 3rd year E.E. student, so have a reasonable idea about the concepts, but I'm not very confident implementing such a system. Moreover, I don't have an oscilloscope, so I'm reluctant to just attack the problem without a solid design, as I have no means of testing it.

Can anyone suggest any useful reading, books or otherwise?

Thanks!

 

I doubt it's practical without a licence, assuming you could even be assigned one?.

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Well, in the UK, there's a few frequency bands available without a licence, such as 27 and 35MHz. They're typically used for model aircraft and similar. I could use one of those, or I could use a restricted band with a power beneath that which would require a licence, which is why I'm interested in ultra-NB.

Edit: This is an example of what I'm after:

Ultra-Narrow-Band Plextek Ltd. Telemetry Radios Optimized For Meter Reading

 

All frequencies in the UK are subject to very strict controls, any licence free areas are subject to very strict and limiting restrictions. It would certainly be illegal (and dangerous) for you to use either the 27MHz or 35MHz RC bands.

Licence free power restrictions require transmitters to pass approval, and to have VERY small powers and short range, 100m is a VERY good range to achieve.

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Ah, ok.
Have a look at the link in my previous post, would you, tell me what you think of it?
...My thinking was that a suitably low power UNB transmitter would only be detectable if you were specifically looking for it.

 

My brother and I have a wireless link between our houses with a line of site problem. We used a high gain directional antennae (dish type) to shoot through a few hundred feet of trees and then about a half mile to a old windmill tower the does a 90 degree turn and repeat to get the signals the other 100 yards to his house.

Using the high gain dish antennae and off the shelf wireless routers, four routers set up with four dish antennae can easily cover 10 plus miles of open land.
Starting with a simple router and dish as the first end, then five mile gap, another dish and router to router link then another dish, (for the repeater station) then the second five mile gap followed by a the last dish and router to connect the end point to.
I have heard that this can be done with a number of router to router repeaters to get around land obstacles and can cover vast distances while still providing a good reliable link.
Each repeater station router pair only needs about 5 watts of peak power input from a 12 volt source. That makes a deep cycle battery and solar power source viable if the repeaters dont have access to a local land power source.

100% legal, off the shelf, and rather cheap too!

Standard issue satellite TV dishes with a properly made antennae board can cover that distance easily as well.

with some scrounging and on line buying a 10 mile capable single repeater system can be built for under $100. Mine was!
For system security the routers can be coded to only talk to each other as well!

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Assuming it's legal in the UK, and either licence free or licencable, and does what you want, it should be fine?.

If you cause interference to other users you WILL be looked for, and penalties in the UK can be quite severe. Bear in mind, if you cause interference in an amateur band, you will get highly skilled people searching for you

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Sounds impressive! Unfortunately though, it's not really what I'm after; as wifi is high-bandwidth and power-hungry, and requires, like you say, highly directional antennae. I want to approach this another way: Instead of sacrificing omni-directionality for range, I want to sacrifice transmission rate for range. If I can produce a suitably sensitive detector, that should be possible.

 

Digi sells long range zigbee modules.

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- Ha, I'm aware of that!
However, it wouldn't cause interference, as the power output would be very, very low. 'QRSS' is apparently the sort of thing I'm interested in; it's been used to transmit across the atlantic, with transmitter powers in the range of milliwatts. Data rates consequently suffer hugely - (words per hour!), but I'm interested in using a much less extreme version of this. Check out this link; it's pretty impressive stuff anyway!

QRSS and you (About VERY low-speed CW)

 

Not to be a 'dit picker' but whats the point or purpose of words per hour rates?
A full page of text would be able to be sent via the postal service from the far side of the world faster!

__________________
"The squeaky wheel often squeaks because its the one carrying the heaviest load." -- tcmtech
"Make me laugh, think and argue and I will call you my friend" -- tcmtech
"If you have to ask for help on an IQ test, you're really not getting the point." -- tcmtech

 

Not on UHF it hasn't

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[QUOTE=sleeper1987;761587]Well, in the UK, there's a few frequency bands available without a licence, such as 27 and 35MHz. They're typically used for model aircraft and similar. I could use one of those
QUOTE]

As a model R/C flier I have every interest at keeping the airwaves allocated to us interference free, I also have a responsibility as a flier to report any erroneous interference to the aurthorities.

I would strongly recommend you do not pursue the constructon and use of equipment utilising any of the allocated frequences for R/C use.

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Just out of curiosity, what's the difference between the public using a 27MHz band for controlling a hobby aircraft or the public using a 27MHz band for controlling some other hobby item?

Is there some specific clause stating exactly what type of devices or activities are allowed to use the band?

 

Yes, only radio controlled models are allowed in the radio control bands, using approved radio systems - and ONLY aircraft are allowed in the specific aircraft band, not even any other kinds of models (for obvious safety reasons).

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