LoRA Antenna

LoRA antenna

Because I didn't like to have a indoor antenna on my LoRA gateway and I wanted to expande the range of it, I desided to make a simple  6dBi Collinear Antenna  as build for 2.4Ghz by MartyBugs. It's a simple non-nonsens design which has proven in time.

I calculated the dimensions for 868Mhz and the sketches can be found below.

Edit : I made a big mistake in the drawing and the first prototype of the antenne. I didn't correct the 3/4 section and the <3/4 section sizes. 

Correct values would be  : Connector - 173 mm - first loop - 346*3/4 mm - second loop - 320*3/4 mm

After the inital building and tweaking I took the antenna to my local Hamradio club (Veron/VRZA Twente) to have it tested with a RigExpert AA-600  (which when connected to the computer can work up to 1.4Ghz) from a fellow Ham. Some minor tweaking (adding 2 cm to the top section) the SWR dip was right on the 868Mhz.

I forgot to make pictures of the build, so I took it apart again to make some.

Close-up from the loop. Remember both have to have the same direction.

The wire and the back-side from the N chassis part. and the 32mm PVC end-cap.

The 52mm car exhaust clamp

other side

The front side from the N chassis part.

Boxing it all up again.

After that, everything was put together again for the final indoor test (it was raining cats and dogs so the installation outdoor will have to wait a day).

The first result are very promissing. With a testnode I transmitted a series of messages from the same location. With the indoor antenna I got a average RSSI of -65 with the indoor antenna (Gateway setup in the window) to a average RSSI -49  (even got one -44) with the new outdoor antenna (in the window).

But the prove is in the pudding, so that evening I did the test again.

New test run with the Lorank8 gateway with the original indoor antenna.

Average RSSI : -64.1

New test run with the Lorank8 gateway with the new outdoor antenna (used indoor on same location).

Average RSSI : -50.8

Hmmmm not the average I got this afternoon. Maybe there is more interference in the evening on the 868Mhz (it's a shared ISM band so maybe there are headphones and babyphones up and running). But then again, RSSI from -64.1 up to -50.8 and that's a good improvement.

Goint outdoor

Then there was time to install the antenna outdoor. I thought I could replace a old MiniWhip antenna of my but that locations was blocked in one direction with my main hamradio antenna mast (I have been using the MiniWhip for SWL listening for ages). So I had to find a new spot.And with a bit of labor, sweat, a touch of "Geveltoeristme", and drilling a hole to get the antenna cable in the shack (the Dormer has a 15cm thick wall), the LoRaWAN antenna was installed on the left side of the dormer.

I can't raise it that high because it will cross paths with my 2m 9elm Yagi and I'm sure the Yagi will win. But for now it will do (maybe in the future I find al better spot on a higher building).

And there it is.

The results :

Well that depends on what you want. Ofcourse there is more coverage then with the original indoor antenna. And on some points even better then when I tested the outdoor antenna hanging it in the window of the dormer. But having it raised above a zinc roofing it will have a slight negative effects when the nodes are in the right of the outdoor antenna (especialy when near).

My daughter volunteerd to help with a field test. I asked her to make 3 measurements on serveral locations so I could log the RSSI. I have plotted the results in a MyGoogleMap which can be accesed  on this link.

Overall the antenne works well outdoor and most locations have a RSSI of atleast 2 points better and we found a max of 17 points (Sample Point 5). Indicating it all depends on the surrounding area (reinforced concrete, solar pannels on roofs etc) .

To our big supprise we  found out that the Node could be spot from my parents house location (Sample Point 7) with a RSSI of -115. Something that wasn't possible before.

Update : There is a other great tool to get info about you gateway : TTNMapper. It's a Android app which you can install in you're smartphone and combined with a node it gathers info about you're gateway coverage (FAQ).

I used it a few times to create a map of the coverage from my gateway. The result can be found here : link.

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