I've been experimenting with ways to improve FPV range inexpensively, and here's what I've come up with:
1. I replaced the 5.8 GHz clover leaf antenna on my FatShark goggles with a helical antenna (and learned to use my own head as an antenna tracker).
2. I boosted my 2.4 GHz radio control signal with a 2-Watt WiFi booster.
I used this 7-turn Right Hand Circular Polarized (RHCP) helical antenna from BEVRC. It's cheap (only about $16) and has a 10 dB gain. I found this works better than using a patch antenna because interference from reflected signal is less of a problem. Make sure the direction of polarization matches that of the cloverleaf antenna on your aircraft.
|Cheap 5.8 GHz RHCP 7-turn helical antenna from BEVRC|
WiFi Signal Booster
This cheap 2-Watt WiFi signal booster works with any 2.4 GHz radio, just connect it between tx module and antenna with the included coax cable.
|Cheap 2-Watt WiFi Signal Booster|
The WiFi signal booster came with a wall adapter for power. I cut the output cord off the wall adapter and soldered it to the outputs of a SkyRC 10-Amp BEC, which in turn is powered from the 3S transmitter LiPo. I installed the signal booster and BEC to the back of my FlySky TH9X radio using zip ties:
|WiFi signal booster and BEC installed on TH9X radio|
In order to test the FPV range, I took a flight up in the mountains. The quadcopter got 2.3 km away and 600 meters up from the launch point before its battery was half exhausted and I had to turn it back. But the video and RC control were still great at that distance, so I was unable to determine the absolute range of this setup. Enjoy the video recovered from the GoPro:
Other Hardware Used
Airframe: ArduPhantom (DJI Phantom case, stock ESC, props, and battery)
Motors: T-Motor MN2214 upgrade for DJI Phantom
Autopilot: 3DR APM 2.5 with ArduCopter 3.0.1 firmware
Gimbal: Hummer 2-axis brushless gimbal for DJI Phantom
Camera: GoPro Hero 3 Silver
GPS: 3DR ublox LEA-6H
Telemetry: 3DR 433 MHz
R/C: FlySky TH9X(ER9X FW) + 2.4GHz FrSky DJT module, V8R7-II rx
FPV: ImmersionRC 5.8GHz 600mA tx + CL antenna, FatShark Predator goggles
Ground station: Mavbot Finder