Supplied Rubber Duckies
The rubber duck antennas that come with the Lora TTGO boards are next to useless so do not bother even trying to use this type of antenna as they are only good for short range. The one that was supplied with my TTGO Lora board was a Lilygo 868 and you would be excused for thinking this was tuned to 868Mhz, but as you can see from the plot below although the antenna has a wide bandwidth the VSWR never gets below 1.7 / 1
Roll your own
I had some SMA bulk head connectors lying around from a batch of ten I bought for four quid from AliExpress which I had bought for the 2M LPF project and after looking on the web I decided to make a simple 1/4 Wave vertical. A quick Google for “1/4 Wave Vertical calculator” took me to https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/ As Meshtastic transmits at around 869Mhz I decide to use this as the desired frequency. I entered 869 in the Frequency box hit the “Calculate My Quater Wave Button” and got the following results
I cut 5 pieces of wire from the secondary of an old toriod transformer which is about 1.2mm ECW , these were cut well over size so that I could trim them down once the antenna was assembled to get the best SWR. I carefully stripped the enamel off of one end of each wire and tinned it, then tinned the SMA bulkhead connect on the pin side of the socket, then soldered the four ground wires at each corner of the socket so each wire was 90 deg from each other. This is quite tricky but I mangaged to get the wire quite straight to each other considering I have fingers like sausages. For the radiating element I enlisted the help of a friend to solder the wire whilst I held it in place. I then bent the four ground elements by eye to 45 Deg then cut them to length 1mm at a time until I got the desired SWR at 869Mhz
Picture below showing a close up of the 4 radials soldered to connector
Then the completed antenna, it looks quite big for an 868 Mhz antenna but that just the camera lying
Finally the completed antenna on the Meshtastic module held up by a semi rigid pig tail
