FPV Antennas

Just a place to accumulate basic DIY Antenna Info

These notes apply to 2.4G and 5.8G CP (circular polarized) antennas commonly used for FPV video. These designs can also be used with 2.4G RC to increase range and/or reliability.

Helical for 2.4GHz

Based on the Helical by IBCrazy info from RC Groups.

For Airwave channel 4 on 2468 MHz using a light weight plastic cross support.

  • Cross support width: 87840/2468 = 35.6 mm
  • Coil spacing: 73660/2468 = 29.8 mm
  • Reflector: 297993/2468 = 120.7 mm (round reflector is best)
  • Coil wire: thicker is better. Number of turns: 3 to 8 is a good range.

There are various matching options. I have used the wave-trap on 5.8 GHz with success.

  • Advantages: Easy to make, Increases antenna bandwidth
  • Disadvantage: No significant
  • Length = 37200/2468 = 15.1 mm
  • Length = 18600/2468 = 7.5 mm
  • Start point distance away from coaxial feed in inches = 730/f in MHz
  • Simply solder this to your helix. The center of the match should be the center of your first 1/4 turn

Notes:

Clover-Leaf for 2.4GHz

Based on the Clover Leaf by IBCrazy info from RC Groups.

For Airwave channel 4 on 2468 MHz using a small double-sided PCB disc to attach coax and wires.

  • 3x Wire length: 307022/2468 = 124.4 mm
  • Bend all 3 wires RA in from each end: 76755/MHz = 31.1 mm
  • Wire: thicker is better.
  • Connector: RP-SMA Male crimp for LMR195 C-SMA1-195 (socket inside)
  • Cable: CA-195 low-loss 50ohm CA-195 Velocity factor: 80 (1 wavelength = 97mm at 2470MHz)
  • RH-CP is when the elements go up to the right. LH-CP is when the elements go up to the left.

Skew-Planar for 2.4GHz

Based on the Skew-Planar by IBCrazy info from RC Groups.

For Airwave channel 4 on 2468 MHz using a small double-sided PCB disc to attach coax and wires.

  • 4x Wire length: 307022/2468 = 248.7 mm
  • Bend all 4 wires RA in from each end: 76755/MHz = 31.1 mm
  • Wire: thicker is better.

Initial antenna tests

10mW 2.4GHz FPV transmitter

10mW FPV transmitter

September-23-2013. Late afternoon I did a 2.4G FPV range test at the Hutt River. It’s over 2 years since I’ve seriously flown 2.4G FPV.

With a camera, 10mW transmitter and battery on a stake and the cloverleaf antenna about 1.2M AGL, we wandered off with the receivers, antennas and small monitor.

I was comparing a 2.4G skew planar (CP) and the quad patch (linear) I built a few years ago.

Skew Planar and patch are probably not the best match, but I haven’t made the helical yet. The patch worked best when lying on one side; linear horizontal polarization.

Except for drop-outs when bushes got in the way, the image was good on the skew-planar out to 700 meters. Trees blocked the view from there to 1300 meters where it was just working and very noisy.

The patch worked out to 1500 meters, where we ran out of easy LOS and gave up.

There was some video interference on both antennas but I’m pretty sure it was coming from our cell phones which both had wifi enabled.

2.4G receiver test at 700 meters

700M from transmitter

From this I’d expect the tiny 10mW transmitter to be flyable out to at least 1KM in an area of little 2.4G noise, and 2 or 3 KM with a Helical receive antenna. This test was along the river bed. With the VTX say 15 meters up it should be much better.

It shows how the guys in Europe go 10+ KM on 2.4G with 500mW or so. Antennas make all the difference.

I got home and was looking at the results when I realized the transmitter was still operating on the stake at the river, and had to go get it.