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HF Radio for data communication

brains93

Hello Guys & Girls,

 

I have an allotment which I am in the process of "making smart" i.e humidity, temperature and moisture sensors, this is all going well and to plan for the moment, but I had a thought it would be nice to have the data sent back to my house where it could be stored and processed, I was even thinking i could make a basic app to show the current or past data. This is not essential as I want the loop to be self contained i.e if it needs water it will auto-magicly open the valve to the rain water tank and pump water out to the plants without my interference needed.

 

The data collections is just a "Lets see if I can" scenario but I am quite new to the electrical building world, so I thought I would get some advice from the experts before I blow anything up. I think the easiest option would be to use a USB data dongle and a sim card to get 3/4G connectivity and send the data back that way, but where is the fun in that.

 

In one of my jobs I use a lot of radio equipment and I am fairly o fay with it, my thinking was I could set up a small radio transmitter (it would have to be 4W or below in power output in order to stay on the correct side of the law) and have it transmit Morse to a receiver at the house which will be hooked up to a raspberry pi to decode the Morse (Transmitting Morse means it should be able to go further on smaller power levels), My house is about 5 mile or so away from my allotment which I think with a bit of tinkering and testing I should be able to get a signal to the house using a sky-wave propagation method which means I need to use between a 3Mhz and 30Mhz frequency range (HF).

 

As I said I am far from an expert on any of these fields so any words of wisdom, advice, warnings or manic twitching would be appreciated. image

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  • 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.

Reply

  • 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.

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