HF Radio for data communication

I would look into using XBee. The have modules which can reach ranges of 40 miles. But they have modules that have a range of 6 miles which would work for your specific case (you may want to opt for the 15 mile module though). It runs at 900 MHz but uses an antenna to boost the range.

You can read more about them here: https://www.sparkfun.com/pages/xbee_guide

However, you will not be able to buy them from sparkfun as they are a retired product, but many other sites do have them for sale.

Hi Grant,

There may be issues with telemetry type stuff at the HF band, as I understand it cannot be an automatic transmission unless someone is physically present near the device, for the amateur radio bands. I could be totally wrong.

Anyway, there are alternative ways which will be easier and cheaper. There are not a lot of integrated chipsets to do HF, whereas there are plenty that cover unlicensed bands known as ISM 'sub-1GHz' and they include 433MHz space, and some space at 868MHz/915MHz depending on the country. No need for HF style propagation off atmosphere with them.

There are requirements on power (nowhere near 4W) and duty cycle. Ordinarily you may have trouble reaching 5 miles with (say) FSK on these bands with low power unless it is line-of-sight, but there are some techniques that will allow excellent message recovery, they rely on spread spectrum methods for the transmission.

If you're using something like Arduino at your sensor locations, then you can get plug-on radio boards, with protocols that are packet-based, so they handle the encoding, you just need to supply the desired bytes. There is a small bit of programming involved to set the frequency, poll the device (or use interrupts) etc. Check out LoRa, there are SX1276MB1MAS and SX1276LB1LAS boards. You still need a good antenna but 5 miles should be very feasible unless you're in an extremely built-up area. Apparently you can cover a large chunk of Manhattan with these devices, with good antenna placement.

There are also paid services on the sub-1GHz bands, but I've not used them, they are operator-dependent and you may get a different quality of ordering experience depending on which country you're in.

In summary, if you're ok with a bit of coding, then sub-1GHz is a good, free option for this distance.

Thanks, My coding skills are firmly in the copy and paste commando range but that sounds good also you are 100% correct on the automatic transmissions but If i have it at a lower power and have the transmissions limited to a set time and length I can get permission to transmit.

Wow they are fantastic bits of kit, I will Have to have a look at them in more depth. I don't think built up areas would be an issue I'm In quite a rural area, It is in a dip but with a bit of heights and gains should be just fine. Thanks

It's a great idea and you've at least thought about some options before posting ...great.

Firstly I think you'll find many of the 'max power' regulations are written around radiated power which includes the aerial system.

Having said that, you can do an awful lot with a good quality yagi antenna at both ends and UHF (433MHz) lends itself very well to that.

Eric showed a few good examples using the RFM69 series transceivers in the Forget-Me-Not Challenge. They have a much lower receiver threshold and all the hard work is done for you.

HF is not very useful in short distances.

It relies on bouncing a signal off the ionsphere and varies depending on day/night. The antenna tend to be quite large as well.

I'm not sure how you'd get on splattering the band with morse code to pass data, but I'm predicting it won't be positive.

The 3G solution is also an idea. We use a similar system for getting data from remote sites. I know that TP-Link MR3020 takes a USB dongle for data, and has great features. Portable 3G/4G Wireless N Router - TP-Link

I suspect that once it's up and running you'll want to add motion dection camera and then the 3G comes into it's own, and with the WiFi aspect you can probably link directly and whenever you're on site.

Having your system automatic is ideal, but be aware that you might want to ensure you have a belts and braces approach to detecting that the instruction did actually work.

I have known a simple watering system continue to water when it quite happily thought the valve was off

Mark

I think an ideal technology for your application is LoRa. It is low power and can easily reach 5 to 20 miles.

There are many low cost modules that implement LoRa including LoPy which has built-in Python.

Hi Mark,

Thanks that Challenge is an interesting read and definitely gives rise to a few ideas.

I had a chat last night with the amateur radio society in the area, lets face it these guys know more about radios than anyone at my job! They had said about the Yagi Antenna and it is definitely an option. I will probably go down the VHF or UHF route after hearing everyone's advice but in case it is useful to anyone I thought I should expand on what I was planning with the HF.

The HF antenna I was intending to use was going to be a more passive approach to sky-wave i.e not a full dipole while that would be an option using 1/4λ and keeping the frequency high to shorten the antenna length there are also devices i could acquire from my work which can be set to move the height of the antenna in order to adjust for night time atmospheric changes. BUT the way I was thinking was to use an inverted V antenna.

Now Keeping the Antenna length small would be key but with a bit of fiddling and the help of a coupler this could be mounted on top of a shed and be "relatively" low footprint, I can then bring the two 'Legs' closer to narrow the beam and make it very directional (a poor mans Yagi) and due to where I live any "overshoot" of the signal would be out the Sea (and is Isle of Man/England's problem after that **Joking of course***)

As I said it sounds like VHF and UHF would be far better plans but I thought I should share my thought process in case it could be of help to others