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

WIN a T-MOTOR 9*3 Carbon Fiber Prop Set for DJI Phantom

Starting September 28, 2013 and ending October 5, 2013 (23:59 PST), MavBot is running a Facebook Page Promotion 'Win a T-MOTOR 9*3 Carbon Fiber Prop Set for DJI Phantom' at http://bit.ly/1fS1BQn . This page contains this Promotion's Official Rules.

'Win a T-MOTOR 9*3 Carbon Fiber Prop Set for DJI Phantom' Sweepstakes - OFFICIAL RULES

NOTE

This promotion is in no way sponsored, endorsed or administered by, or associated with, Facebook. Participants are providing information to MavBot and not to Facebook. The information provided will only be used for administering and communicating with participants about MavBot and the MavBot promotion they are participating in.

SWEEPSTAKES DESCRIPTION

T-MOTOR will soon introduce a set of four 9*3 antiGravity! Carbon Fiber Props for DJI Phantom. Have a go at being the first to fly a set of these revolutionary, all-white props with a retail value of $89.90, by entering MavBot's Sweepstakes today!

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The Sweepstakes entry period begins at 00:01 a.m. PST on September 28, 2013 and ends at 11:59 p.m. PST on October 5, 2013 (the "Sweepstakes Period"). Winners will be randomly selected within 24 hours, from entries properly submitted and timely received during the Sweepstakes Period.

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Prize: One T-MOTOR set of four, all white, 9*3 antiGravity! Carbon Fiber Props for DJI Phantom with a retail value of $89.90.

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FPV Crash into Obstacle on RTL

This was the first time I've crashed while flying FPV. Crashes are usually caused by a series of mistakes, and this crash was no exception:

Mistake #1: Some of the hills around the flying area rose to at least 100 meters above the launch point, but I had the Return to Launch (RTL) minimum altitude set to only 50 meters above launch altitude. Note: I later realized that setting the RTL alt even higher wouldn't have helped anyway, because the current ArduCopter code foolishly limits RTL height to 80 meters).

Mistake #2: I flew behind the hill at such a low altitude that the forest cover on one of the hill's ridges came between me and the vehicle, thus scrambling my video signal (the 5.8GHz video is so high frequency that even vegetation can scramble the signal quite easily; whereas my RC control on 2.4GHz remained solid through the entire ordeal).

Mistake #3: Upon losing the video I did not back up or gain some altitude, but instead just kept going forward for a couple seconds, hoping video would come back. This just made the problem worse.

Mistake #4: When the video signal didn't come back, I switched into autopilot-controlled RTL mode, without gaining some altitude first. Thus the autopilot, already well above the set RTL minimum altitude, simply initiated a high speed beeline back towards the launch point...

RTL Code Change:

To help prevent this kind of accident happening again, I made a change to my local ArduCopter code to make it so that RTL always climbs first before heading back to launch, no matter what altitude that RTL is invoked at (although my code does provide for an absolute altitude limit if the Fence feature is turned on).

I've been using the code for a few weeks, and found that it makes FPV flying much safer, without having to set an inconveniently high RTL altitude; especially in high mountainous terrain or around tall trees. I submitted the code as the RTL Always Climb pull request to ArduCopter.

Hardware:

Airframe: ArduPhantom (DJI Phantom case, stock ESC, props, and battery)
Motors: T-Motor MN2214 upgrade for DJI Phantom
Autopilot: 3DR APM 2.5
Gimbal: Hummer 2-axis brushless gimbal for DJI Phantom and GoPro 3
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 + 2W WiFi booster, V8R7-II rx
FPV: ImmersionRC 5.8GHz 600mA tx + CL antenna, FatShark Predator goggles + 11db patch antenna
Ground station: Mavbot Finder (first time actually used to find lost aircraft!)