Building a LoRaWAN home network

I eventually went for a small SX1301 based LoRa gateway from RAK Wireless, the 831 and now have that running in my house network. Radio frequency work is different to SBC/MCU work and is a lot more ‘physical’ in the sense that you need to think about the radio frequency and antenna patterns. That’s a whole new / old world for me – and one which I thought I’d left from my childhood days.

I grew up in a country town where one of my leisure activities was being part of a ‘radio club’ for amateurs, also known as ham radio enthusiasts. These were the days of CW McCall and the song¬†Convoy so I heard a lot of 10-codes used when travelling in cars. Our radio club toured commercial radio sites as well as taking part in radio jamborees, and constructed some monstrous antennas to pick up radio signals from all over the world – so I got familiar with terms like baluns, impedance matching, dipoles and yagis.¬†Radio is amazing, does weird things and in my estimation just a little easier to understand than quantum mechanics. I never did get my Morse radio license though it may have been useful, and regret that now.

Setting up the RAK831 with a partner Raspberry Pi, initially using the jumper wires to connect them was easy and I soon got a signal through on LoRa. It seemed pretty simply just to follow the recipes on the internet as the device is based around a IC880a chip and there are plenty of code examples up on GitHub. My node devices are LoPy from Pycom and as they used MicroPython are pretty familiar from my work around e-ink displays. I registered the gateway with The Things Network and have it receiving stuff now, even if it is sitting on my filing cabinet and needs to be placed into a IP56 gray box and fixed to the wall.

I drilled through my house outer wall and poked the antenna out there, one of those ‘rubber duck’ type mono-pole ones, I think it is quarter wave but works quite well. Then registering on the ttn-mapper website allowed me to start mapping the reception from a smaller, hand-held LoPy transmitting a sequence of “1234” in a 30 second delayed loop so as not to abuse the duty cycle of the 868 ISM band. The results were both disappointing and amazing – amazing that such a short antenna transmitting/receiving can get anything and pass it back to the internet, and disappointing that it can’t be heard in behind some local buildings.

Screenshot from 2017-10-07 09-14-36

I’ve a couple of thoughts on this: a quality antenna such as a half- or full-wave may be better, orientation of the receiver (it is horizontal now) may be important, elevation could be critical, and not placing it on one side of my house but instead the roof so that it isn’t blocked by a close building may all improve things. But for my first simple use case that I want to merely ‘hear’ my small environmental sensors I think what I have now is probably sufficient!

Advertisements