OpenEnergyMonitor Community

EmonTH range testing for greenhouse

I am using an Emonpi to monitor my solar production and electricity consumption.
I would also like to monitor the tempertature and humidity in my greenhouse, which isn’t very close to my emonpi (Maybe 15-20 meters away). This should be within WIFI range, but i doubt UHF RF range.

Is there a way of testing the range of the UHF RF module before purchasing the EmonTH? And if not, what is the easiest way to set it up in terms of hardware? Would i need to buy emonbase to make up for the distance? Would that even help my situation?

Any help appreciated, cheers.

Edit - Added the term UHF. BT, Moderator.

Why? Are there serious obstructions between the emonPi and the greenhouse - I’m thinking of a thick stone wall, or a wall that’s solid metal or filled with foil-backed insulation, or multiple brick walls? The RFM69 operates on 433 MHz, a much lower frequency than Wi-Fi, so the range should be better, not worse.

The claimed range for those radios is well in excess of your 20 m, approaching an order of magnitude better, given a clear line of sight.

The only way to test is with another transmitter, the emonPi does indicate the received signal strength.

Note that you can improve the efficiency of the aerials with a ground plane.

@Bill.Thomson might offer some better advice - it’s his line of business.

Thanks Robert. I didn’t realise that the 433 rf band is so much better at distance than wifi, but it makes sense when I think about how poor the 5ghz network is compared to 2.4.

My emonpi is situated in a meter box on the side of the house, which has a steel cover. This reduces the wifi signal signicantly and I have to leave the cover adjar to get signal. The house runs for a bit and then around the corner to the greenhouse. Based on your info though, I might just give it a go and if it doesn’t work I can just ad a base station later I guess.

Thanks for the input.

I’d be much more inclined to buy an extension cable for your emonPi’s aerial, and move that outside the box. Unfortunately, it won’t help the Wi-Fi (that’s on board the Pi) but for that, you could disable the internal Wi-Fi and add a USB dongle on a USB extension cable, or if your router is the other side of the wall, an Ethernet cable would solve the problem.
Or, could you move the emonPi out of the meter box and into the house, and extend the c.t. cables?

Hi Scott,

I take it your meter box is mounted in the wall flush (or nearly so) with the wall surface?

Hi Bill, yes you are correct. Flush with the wall and out of line of sight.

Thanks for the tips Robert, i didn’t think about getting a simple extension cable for the emonPi, that seems like a great solution. I could mount the emonPi externally, but it would be more exposed to the elements and only protected by the eave.

Points to bear in mind for UHF antenna feedline.

  • Keep the total length as short as possible
  • Use good quality coaxial cable
  • Be aware of Reverse Polarity connectors
  • If you’re not comfortable soldering / assembling RF connectors, (it can be tricky) you can buy a pre-built cable assembly

I recommend not using RG-58 or RG-174 cable as both are very lossy at 433MHz.

However, if the length is kept short, e.g. 1 or 2 meters, the loss is kept to a minimum, and their small
size and flexibilty can actually be a mechanical advantage.

Here’s an example of a better quality assembly:
(They’re proud of it too. ~30 bucks)

And here’s an example of one made from the smaller (lossier) coaxial cable: