Tuesday, January 21, 2014

1.3 GHz FPV Testing

Although our 5.8 GHz FPV setup works fairly well, I would prefer a video system that doesn't get all scrambled just flying behind a few trees, and that has much better range than just 2 km.

I thought we could do better with 1.3 GHz, so we've been experimenting with that. The first major test was this flight a bit over 2 km up a mountain valley near Baiguo.

1.3 GHz FPV Equipment used:

2x Circular Wireless 1.3 GHz SPW12 Skew Planar Wheel antennas
ReadyMadeRC 800mW 1300MHz Transmitter (2-channel US-legal version)
ReadyMadeRC 900MHz-1.3Ghz Receiver SAW w/1258 Custom RMRC Version 3
ReadyMadeRC Low Pass Filter for 1.3GHz Antennas (on vtx to help prevent GPS dropout)

Unfortunately, my tests so far have shown that the range is about the same as we used to get with 5.8 GHz and the Circular Wireless 5.8 GHz helical antenna. Of course it is nice to no longer have to keep turning your head to track the aircraft, but I'd prefer a solution where I can fly behind a few trees without losing most of the video signal. And in terms of that, 1.3 GHz FPV seems to be performing even more poorly than 5.8 GHz.  At least with 5.8 GHz I could fly behind maybe 6 to 10 trees before losing the signal completely. But in recent 1.3 GHz tests I lose the signal through just a couple of the same trees, and get glitches in the video just flying behind a single tree only 50 meters away!

So what's going on here that 1.3 GHz seems to have such poor tree penetrating power compared to 5.8, when supposedly it should actually be better? Interestingly, I've noticed the 1.3 GHz does penetrate concrete walls and rocks quite well, in fact much better than 5.8 GHz! So it's only trees in particular that seem to not like 1.3 GHz and prefer 5.8 GHz instead!

So if I want to reach my goal of flying FPV through trees with good video, maybe I'll need to try a high-gain antenna and an antenna tracker with 1.3 GHz, or perhaps move to 900 MHz video.


  1. Expect to lose 10db per (leaf-bearing) tree top that your signal bisects for 900Mhz.

  2. Regarding the impact of trees (and rain!) on 1.2Ghz you'll want to understand the interaction of signals in that band with water molecules. That will help explain what's happening.

    1. Hmmm, so what's the recommended solution for doing FPV under the forest canopy? I've tried 5.8GHz, which barely worked, and 1.3GHz which doesn't work at all. Could 2.4GHz FPV work, considering I've never had any trouble with trees blocking 2.4GHz radio control?

  3. Hi, did you ever figure out what your issue was? I too recently switched from 5.8 to 1.3 and am very frustrated as the video signal was much better on 5.8> i bought what i thought was a quality system too. Readymade rx with saw filter, 400mw vex and circular wireless skew planers on both....now i wish i hadn't sold my 5.8.

    1. I think probably the main issue is that 1.3 GHz is absorbed by moisture, so flying behind trees with a lot of moisture content the signal is blocked. That would explain why flying behind trees at close-range doesn't work, whereas flying behind buildings at close range works fine. Also why flying behind pine trees works OK (low moisture content in the trunks and branches) and broad-leaf trees does not (high moisture content). The speed at which the receiver can respond to signal strength changes is also an issue, as when the vehicle is sitting stationary behind trees there's no problem, it's only an issue when the vehicle is moving. Also, we've switched to a Lawmate tx/rx combo, which gives some marginal improvement. I'd like to try 900MHz video to see how that would compare for flying behind trees.