The project must be able to detect the amount of water in tanks and transmit the information to a farm house it must be wireless and unfortunately there is no cell phone reception in the places that need to be monitored.

I have a way of measuring the water that is pretty easy, going to use ultrasonic distance measuring and some maths unless anyone else knows something better?

My problem is to transmit around a max distance of 400 km and must be done with as little power and setup as possible. Going to be using solar panels and will research that later but for now its getting the comms down.

Does anyone have suggestions for the equipment to use for this project? I have looked into a few applications but most require big antennas that need to be setup. The transmission rate is not a problem as it can be as slow as needed really because of minimal data to be sent.

The line of sight is not too great as I'm told but not horrible either.

I would like to use Arduino as I am familiar with it. Repeaters are an option, but would increase the cost a fair amount.

I am willing to get a HAM license but would prefer not to as I'm not really going to use this for "talking" just sending data once every day or so.

Any suggestions and pointers would be of great help.

  • \$\begingroup\$ Oof. I don't think you're going to find something that can do 400km easily, LoS or otherwise, without bouncing off the ionosphere. \$\endgroup\$ Commented Aug 19, 2014 at 6:26
  • 1
    \$\begingroup\$ Do you really mean 400 kilometres or metres? | It's unlikely there is no reception over the whole 400 km range if it is km (although, as you are in South Africa, this is possible)(but unlikely), so, if cellphone is acceptable the 400km is a "red herring". You need to provide a better explanation of context. | If it IS 400 km and you only want a report per day or so, is there a public transport system there - bus or minivan or ... . A very simple transponder can mount on a vehicle and provide a data transport (literally) system. [Like sneakernet but different]. Yes - this has been done. \$\endgroup\$
    – Russell McMahon
    Commented Aug 19, 2014 at 6:45
  • \$\begingroup\$ Do you have very high ground nearby at either end - range can be much greater. You can link from site to high repeater. Are there any radio telephone or telemetry networks nearby? How far to nearest cellphone sites? \$\endgroup\$
    – Russell McMahon
    Commented Aug 19, 2014 at 6:48
  • \$\begingroup\$ To get cellphone coverage, up to about 50 to 100km, if some cell phone company has hill top long range sites, use a cell phone Yagi antenna of about 1 to 1.5 meters long. Best to use car cell phone as they are much more powerful than hand held cell phone. If not, need to open the hand phone to connect the antenna via test connector that are hidden inside many hand cell phone. Cell phone is best cost. Try good antenna and you may got it. Dual band cell antenna cellantenna.co.uk/index.php?id=yagi \$\endgroup\$
    – EEd
    Commented Aug 19, 2014 at 7:25
  • \$\begingroup\$ Yes it is 400 kilometers and on farms here there are plenty of places that companies just don't see the need to get signal out to unfortunately. I'll have a look at the antenna options they look promising in this situation I think , thanks for the help \$\endgroup\$
    – Spider999
    Commented Aug 20, 2014 at 0:31

2 Answers 2


There are a numbers of satellite transceivers, as PCB modules (size of a few coins) or boxed-product, that are low power, easy setting up and come with driver library example code.

Some low-speed equipment is not especially expensive, however, there are data volume charge which may be acceptable if you only send small data once every day.

Two types, those use LEO (Iridium and similar) does not demand very open sky view as sat is high elevation angles. Those use geo stationary sat (Inmarsat and similar) need open sky toward 'generally south', depending on Latitude.

These sat have high, medium and low speed units. Low speed, non-voice units are what you need in terms of cost, easy setting up, low power etc.

SBD Short Burst Data Satellite module

Another similar unit from another brand and service provider

For the ham path, you can use PSK31 HF modem which allows low speed (31 bauds) transmission with small antenna and easy setup than traditional HF modems of higher speed (few kilo BPS). Wiki on PSK31

Ham band need

a) knowledge to choose different freq depending on day, night, seasons, latitudes and solar cycle

b) depends on countries, may not be full legal for machine-to-machine communication not carrying 'ham traffic' (some country defined as self-training activities)

OR, can get a commercial license and use HF band (not sure how hard it is) and same ham equipment

OR use the HF network (fee based or not, 100% sure) for file and email for small yacht at sea. Check SailMail or similar

  • \$\begingroup\$ Agree that Satellite is the best if you don't want to use HAM. You can only use ground wave radio (<2MHz) or F1/F2 reflection (up to 30MHz). Any (ISM) frequency higher than that needs a line of sight isn't possible at 400km. \$\endgroup\$
    – RJR
    Commented Aug 19, 2014 at 7:27
  • \$\begingroup\$ Thanks I'll have a look into those options dont think ham is an option then because I would like it automated as to make the system as simple as possible and not have to adjust it each day for best conditions \$\endgroup\$
    – Spider999
    Commented Aug 20, 2014 at 0:29
  • \$\begingroup\$ Sat is simple and as used in many real life professional systems. It is like SMS on phone. Send a formatted data, says, 50 bytes long, to the unit and it will send out for you. On the receiving end, it can be via internet and/or another sat unit. You buy a service plan of 'nnn kilo bytes' \$\endgroup\$
    – EEd
    Commented Aug 20, 2014 at 3:45

If it is 400m rather than 400km you might try laser communications modules for Arduino eg

Laser Transmitter Sensor Module for Arduino

  • \$\begingroup\$ Hey no it is 400 KM that's the problem unfortunately but those seem good for another project to play with thanks \$\endgroup\$
    – Spider999
    Commented Aug 20, 2014 at 0:26

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