Sunday, September 29, 2013

Longer Range FPV for Cheap

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.

The Antenna

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
This antenna gives excellent range as long as I point it directly at the aircraft and it has line-of-sight. Reception through trees is still quite poor. It takes some practice to get used to pointing your head at the aircraft while flying FPV, but soon it becomes second nature.

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

Range Test

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


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