Ultra-Narrow Band Radio link - where to start?

[sleeper1987]

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!

 

[Nigel Goodwin]

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

 

[sleeper1987]

@Nigel

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:

**broken link removed**

 

[Nigel Goodwin]

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.

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.

 

[sleeper1987]

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.

 

[tcmtech]

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!

 

[Nigel Goodwin]

Ah, ok.
Have a look at the link in my previous post, would you, tell me what you think of it?

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

...My thinking was that a suitably low power UNB transmitter would only be detectable if you were specifically looking for it.

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

 

[sleeper1987]

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.

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.

 

[blueroomelectronics]

Digi sells long range zigbee modules.

 

[sleeper1987]

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

- 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)

 

[tcmtech]

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!

 

[Nigel Goodwin]

- 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.

Not on UHF it hasn't

 

[Chippie]

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.

 

[Mr RB]

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?

 

[Nigel Goodwin]

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).

 

[Chippie]

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

It is subjective to the country in which they are to be used..

But yes there is...

https://www.electro-tech-online.com/custompdfs/2009/07/UK-Frequency-Allocations.pdf

27Mhz is dedicated to Glider type aircraft and powered aircraft, 35Mhz is dedicated to powered aircraft,
40Mhz is dedicated to water based craft.

 

[sleeper1987]

Hi again.

@tcmtech
- Very little of the stuff on here has any practical use. This site is used by hobbyists, who're obviously only pursuing their own interests. I'm not in this because I *need* long range transmissions, but because I figure I'll learn something useful along the way.

@Nigel Goodwin - "Not on UHF it hasn't".
- Perhaps not, but my goal was never trans-atlantic transmissions. Furthermore, I came to this thread looking for constructive advice, from people who are clearly knowledgeable about the subject. It's been dissappointing to have only received repeated warnings regarding interference, given that I thought I'd made clear that I didn't plan to violate any applicable laws. This is an electronics forum; I didn't come looking for legal advice. If you feel the need to warn me about breaking the law, it it would have been nice to have had some advice about the electronics as well.

@Chippie
Yeah, that's right. Ofcom have a section on it here:
**broken link removed**

 

[Nigel Goodwin]

@Nigel Goodwin - "Not on UHF it hasn't".
- Perhaps not, but my goal was never trans-atlantic transmissions. Furthermore, I came to this thread looking for constructive advice, from people who are clearly knowledgeable about the subject. It's been dissappointing to have only received repeated warnings regarding interference, given that I thought I'd made clear that I didn't plan to violate any applicable laws.

No, you've made it VERY clear you ARE planning violating laws - many people here (including myself) are radio amateurs, and we take a very dim view of such proceedings.

There are various licence free modules available, I suggest you look at those - although I doubt any are available that will meet your ten mile range?.

 

[sleeper1987]

No, you've made it VERY clear you ARE planning violating laws - many people here (including myself) are radio amateurs, and we take a very dim view of such proceedings.

"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?

 

[Dick Cappels]

Google "wolf lowfer" (don't use the quotation marks). This will give you some ideas. Also, consider QRSS mode (very slow Morse code). Both can span great distances with tiny amounts of effective power. And they were developed for license free use.