Adventures in LoRa & TTN - Part 2, Improving the Gateway!

At the end of the last blogpost I mentioned that the range was FAR off what I should be getting. The whole point of LoRa is that it's long range. So lets try and fix that.

This post is a bit like a journal so parts will be rather mixed and maybe out of order.

Improving the Node's antenna

I'm currently using a LoPy as the node I'm using to ping my gateway, However due to one of the u.fl to sma connectors breaking I had to just use a u.fl connector with a ~ 8.6CM Wire on it which worked pretty well. However I had my LoRa32u4 arrive today with another u.fl to SMA connector and antenna. I connected these up to my LoPy and an improvement!

Upgrading the Gateway's signal

To begin with I just wanted to do a quick and simple upgrade on this. So I ordered a £10 antenna off amazon along with next day delivery to my local locker. I fitted it to my gateway and... No improvement.

I then posted on TTN's Forums and after a bit of debate it seemed that it could be a mix of things including:

  • Height of the antenna
  • Antenna not being that good
  • Other interference.

I begin doing these small improvements one by one to see the effect. While at the moment I can't make a really high antenna as being in a bungalow anything too high would be obvious. I also can't mount an antenna to the house without it costing a lot to do. I can however possibly put an antenna 1-2M High on the garage which is where my gateway is currently located.

Another comment made was that I used jumpers instead of a PCB for connecting the IMST Board which could be cuasing interference.

So let's do each one:

Interferance:

To begin with I wanted to elemenate the simplest thing being inteferance possibly from the Raspberry Pi itself.

There's a few parts. The Raspberry Pi Itself, The interconnect between the Pi and the IMST Board and surrounding environment such as other electronic devices.

  • Wi-Fi & Bluetooth - While it shouldn't affect it as they're both 2.4Ghz bands if you're using a Pi 3 you can disable both by adding the following to your /boot/config.txt file:
dtoverlay=pi3-disable-bt
dtoverlay=pi3-disable-wifi

This made very little difference to the signal.

Next I then thought, lets see what other pats of the Pi I can disable.

I began with disabling HDMI using /usr/bin/tvservice -o and checked the result. The RSSI and SNR Didn't improve any more with my node in the same location compared to before running it.

Next I then tried instead disabling audio out and changed the core clock to 250Mhz instead. And..... No Improvement.

Finally I thought, is the Raspberry Pi the best?

I have a mix of SBCs of different brands too and decided that actually an Orange Pi Zero would be better, It's smaller and more compact while also if in the future supporting a method of POE. While once again no improvement it actually works just as well and is around a third of the price to use in a gateway. Furthermore it means I can use the Pi 3 in another project if required.

Antenna

Finally it came to the antenna, While being told that height would make the most difference I also didn't think my antenna was that great. I got recommended one by @circuitbeard / @mattbrailsford and brought one. (He actually had one spare so I got it from him New Second Hand). I also ordered some RG8 cable (RG58 is claimed to have too high of a loss) and the connectors.

Long story short RG8 cable is a lot thicker than most coax so the connectors I ordered were incorrect. I found the N Connector from Maplin and a SMA Connector from eBay fitted perfect. (Also I originally tried a sequence of connectors being adapted down to SMA however this caused quite high loss exp in a "UHF Connector").

Furthermore by getting this proper antenna it's also designed to be fixed outside, I used a £5.50 TV Bracket from Screwfix and here it is!

Range Testing

I then started testing the range and.... Much better!
Screenshot-from-2017-12-29-12-32-11
Raw Data Points

Screenshot-from-2017-12-29-12-32-49
Approximation of area covered.

Analysis of range testing

Something I've found rather interesting is signal strength, I'd have expected the range to be still quite strong within 1KM and then start to fade out. However from testing as you can see on the raw data point map that after around 500M on average is stays at around -100 to -120 RSSI no matter how far you then get.

Handily TTN Mapper produces a graph of this as well:
rssi_vs_distance

What's next?

The next post will be a further post on mapping. I haven't really driven much around the area so have a bit of driving I want to do to map it out better as a majority of the data so far has been when I've been walking around and popped to the shops in the car. While the antenna I got from amazon was terrible for the gateway it works ideal to put ontop of the car to map it.

I also have ordered a PCB Connector for the system as well so will test and report back to see if it makes a difference.