Discussions

In my attempts to throw together a somewhat long range system for my plane, I've run into a few issues. 

First, the equipment in question is a 500mW 5.8 GHz video tx, and a 433 Mhz RC rx. I'm aware that components like this need to be separated to avoid interference regardless of frequency, power, etc. So I did just that. The video tx was at the front of the plane (HK EPP FPV), and the 433 rx toward the mid/back. The rx is a diversity receiver so I fed the two antennas through holes in the sides and arranged them in a front/back "V" setup. The video tx was connected to its cloverleaf antenna via a jumper (rf extension cable) through a hole in the fuselage toward the front. The tx was placed inside but the antenna outside.

All seemed well, and I even got a couple of good flights in, but then things went downhill. During one of my launches the rx lost contact and the plane plummeted (yeah, I had poor failsafe setup and no APM at the time), and broke. I fixed it up but the mystery of the cause of the failure remained.

I just got done investigating the issue. I discovered that the cause was the jumper from the video tx to the antennna. It seemed to be "leaky" to the point of interfering with the reception of the 433 receiver. To verify, I placed the cloverleaf directly attached to the tx and moved it around to several locations in/around the plane. Interference only showed itself when the antenna came nearly in contact with either the rx or the rx antennas. I tried a more robust RF extension cable I've used for other projects and everything was reasonable as well. I had another of the shorter cables which was the same type as the one causing problems. It yielded the same bad results. The worst results occur when the extension cable is inside the fuselage... Is the EPP foam reflecting the leaked signal within the plane?

After all this, I'm wondering if there are specifications regarding rf extension cables which ought to be carefully considered when using with a system like this. Perhaps the cable was too thin and not shielded enough? Is anyone using cables for extending an antenna with a 5.8 GHz system with good results? Are there known problems (harmonic or otherwise) with 5.8 GHz and 433 MHz when used together?

For now, I will see what I can do to mitigate the interference I'm seeing. Hopefully I'll be able to find something that works!