step by step range trouble shooting
1) Ambient Noise Pollution: With transmitter off, turn on goggles (and wireless receiver) and view image background. The image should be uniform snow with no horizontal lines or artifacts. Interference shows as horizontal lines (or partial image).
Solution: If horizontal lines, change to a clear channel then change transmitter channel to match. If all channels show horizontal lines, you will need to change your location or deal with the short range at that polluted location.
2) Noise from RC Gear: With transmitter off, power all other RC gear (RC radio, quad/airplane/OSD) and check for uniform snow (important to start motors).
Solution: If interference only occurs with RC gear running then you need to filter the power supply to the FPV equipment (or isolate the source of interference).
3) Functioning Antenna: Turn on transmitter/camera only (not RC vehicle or equipment) and move away from source until image becomes snowy (end of range). Remove antenna from headset. Headset image should become noticeably less clear or not able to view. If same, then antenna problem.
Solution: If no change in image, check to ensure correct antenna connector (SMA - not RPSMA - should have a pin on the RF line).
4) Correct Antenna Orientation: Antenna should be pointing either vertically up (usually airplanes/wings/ground vehicles) or vertically down (quads/multicopters). There are nulls on the top and bottom of the antenna so placing horizontal will cause loss of signal when the antenna is pointing at you (note this will happen when flying directly overhead as well when the antenna are vertically mounted).
5) Correct Antenna Placement: Ensure that the antenna portion completely clears the air frame. At these high transmission frequencies, anything can block and degrade the signal. For multicopters, try to get the antenna to extend out and down below the craft (as most of the time muticopter flying is close in and you are generally standing lower than the craft.
6) Correct Antenna Selection: For multirotor craft it is imperative to use circular polarized antenna.
7) Reasonable Performance Expectations: Generally speaking, in ideal conditions (dry, no rain, line of sight, outdoor flying, no buildings around) a 5.8Ghz FCC transmitter with circular polarized dipoles will get about 200m range, a 25mW CE transmitter will get about 500m, a 250mW transmitter about 1km. Range is significantly reduced in urban environments, ground applications and objects between transmitter antenna and receiver (including the aircraft frame).