Directional RF Chamber for 5.8Ghz receivers

Thread Starter

zwirek2201

Joined Nov 29, 2022
2
Hello guys!

I'm one of the organizers and race directors in the Polish FPV micro drone racing league and I've been struggling with our lap timer solution for quite some time.

To quickly describe our setup:

Our laptimer (the device that measures our lap times) is based on multiple RX5808 5.8Ghz receivers. Each receiver is set up to a specific channel and when multiple drones are racing, it gets the RSSI data from all of them and looks for signal peaks. Laptimer is set up next to our start gate and when a drone flies through the gate, laptimer catches that.

The problem with the system is that often (especially on smaller tracks) drones will fly behind the laptimer or even above the laptimer and will get picked up. We managed to limit the issue by putting the lap timer inside of a metal ammo box and directing the open side of the box towards the start gate. It works much better, but it's still not great. When a drone files behind the ammo box, the signal peaks. The peak is lower than when the drone is in front of the box, but it's still high enough that it makes marshalling races very fiddly.

I'm determined to make a better solution, but I'm not sure what the best way would be. I know from our community that some people made enclosures using simple aluminum foil or copper mesh but even after grounding the mesh, the situation is still not great.

I don't know too much about RF, but I'm pretty sure things like mesh size/how it's grounded/enclosure opening size etc. make a big difference.

I'd love any help on what materials are best to use/what are the things to look out for etc. If you have any more questions, I'd love to answer them!

Thanks guys!
 

Ya’akov

Joined Jan 27, 2019
9,264
Welcome to AAC.

Instead of trying to shield the receiver from off axis signals it would be far more productive to use a directional antenna with a high front-to-back ratio which is a measure of the rejection of signals from behind the antenna.

You’ll also want a high gain figure and a narrow beam width. Both things that will reduce signals off axis.

You can also do something to scale the RSSI so that only signals close to the antenna and in the right place will be sufficient to trigger a lap.
 

Thread Starter

zwirek2201

Joined Nov 29, 2022
2
Welcome to AAC.

Instead of trying to shield the receiver from off axis signals it would be far more productive to use a directional antenna with a high front-to-back ratio which is a measure of the rejection of signals from behind the antenna.

You’ll also want a high gain figure and a narrow beam width. Both things that will reduce signals off axis.

You can also do something to scale the RSSI so that only signals close to the antenna and in the right place will be sufficient to trigger a lap.
Hi!

Thanks for the reply!. It sounds like a pretty good idea. I have some follow up questions.
- Do you know if there may be any issues with using one antenna for multiple receivers? Would an SMA splitter work to have let's say 2 directional antennas for 4 receivers?

- Does anything else need to be done to the RX5808 receivers when I run them with antennas? Right now I assume the whole metal part of the receiver acts like an antenna. When I solder an antenna to the antenna pads, would the enclosure still work as an omni-directional antenna and receive signals from all directions or would the directional signal from the antenna be so much stronger that the rest of the signal would be negligible?
 

Ya’akov

Joined Jan 27, 2019
9,264
Hi!

Thanks for the reply!. It sounds like a pretty good idea. I have some follow up questions.
- Do you know if there may be any issues with using one antenna for multiple receivers? Would an SMA splitter work to have let's say 2 directional antennas for 4 receivers?

- Does anything else need to be done to the RX5808 receivers when I run them with antennas? Right now I assume the whole metal part of the receiver acts like an antenna. When I solder an antenna to the antenna pads, would the enclosure still work as an omni-directional antenna and receive signals from all directions or would the directional signal from the antenna be so much stronger that the rest of the signal would be negligible?
Yes, there is a potential problem with using a passive splitter, but you probably need to test empirically. The issue is with impedance matching but you can fix it if it is broken.

I haven’t used that module but looking at the data sheet it appear it is intended to have an SMA connector for an antenna. In any case, there has to be something attached to the antenna terminals. Whatever that is, it has to be detached for your new antenna to function properly.
 
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