I swear by these pigtails for strain relief on your quad. These properly anchor your antenna and securely connect to your VTX. I prefer the MMCX connection for it's durability and ability to release in a nasty crash.

TBS UNIFY PRO 5G8 SMA PIGTAIL (MMCX)

MMCX to SMA Pigtail for connecting SMA antennas to MMCX type VTX