I built my own groundplane antenna and tested the performance for Meshtastic use around 869MHz. Also a quick introduction to simple settings for Nano VNA network analyser.

Some online antenna calculators:
https://m0ukd.com/calculators/quarter...
https://www.changpuak.ch/electronics/...

For more info about Meshtastic activity in and around Brighton, UK see
  / 3696312513946679  
A much larger Facebook group is Meshtastic UK
  / 625434626178266