You’ve done with pretty straightforward hardware setup and almost no software configuration, and saw your first HD stream (on short distance on a table) you probably happy and inspired. But then you probably could face bad reception issues in the field and you became disappointed after numerous config changes that doesn’t help. You may wonder that you probably need better/another WiFi adapters or boosters, or antennas, or maybe all-together. Maybe even considering abandon this project for better days. Please don’t, give it another try. You could be another one among majority who suffered from exactly same RF Interference issues.
Unfortunately, most popular (already laying around) WiFi dongles are 2.4G, most popular RC Transmitters are 2.4, and it is very crowded radio spectrum nowadays: WiFi, Bluetooth, walkie-talkie, car alarms, remote controls, DECT phones, microwave ovens … And of course you choose 2.4 for a longer range since it was mentioned in the wiki.
So before you give-up please consider several known solutions to significantly improve your reception.
All modern 2.4G RC Transmitters are using frequency hopping technique and usually not allowing choosing channels or frequencies so you can’t configure it or your OpenHD to avoid overlapping. It will interfere. Least you can do is to increase distance between ground receiving WiFi and your, or any other, RC. Best solution will be to move out from 2.4 range. Even if you change your RC to any other frequency someone else could have it near to you next time.
Also there is very weird and annoying, hard to guess, interference source - your ground rpi, or more specifically HDMI connection (cable). It generates constant noise in similar frequencies. Observable on 2.4 and 2.3 ranges. Solutions could be different: changing HDMI cable, distancing WiFi dongles away from rpi by adding USB extension cables, shielding rpi, using other possibilities to transfer video (USB tethering, Ethernet, WiFi consider frequency distancing)