Have you had the back of the radio off? The reason I ask is that I've read that some pilots who've opened their X20 have inadvertently dislodged one or more of the internal antenna connectors. That situation would definitely have an adverse effect on RF performance.
Otherwise, the photo of the antenna arrangement in your model raises some other points in my mind:
- The 2.4GHz antennas in the model are oriented more or less vertically. Unless I'm mistaken, both 2.4GHz antennas in the X20S are oriented horizontally. Such a difference in antenna orientation is called a polarization mismatch. It reduces the effectiveness of the RF link. And while the orientation of the receiver antennas to the transmitter antennas clearly changes in flight, your setup is optimized for the model flying either straight up or straight down, not horizontally. Would I expect this polarization mismatch alone to cause the very poor reception you're seeing on 2.4GHz? No, I wouldn't. That said I have encountered several cases where poor antenna placement and orientation have caused complete loss of link in specific orientations of model to transmitter.
- And that last point brings us to the 900MHz antenna placement in the model. It too is more or less vertically polarized, whereas its counterpart in the X20S is again horizontally polarized. The fact that there's only one 900MHz antenna in the model and in the transmitter makes this situation more problematic. In fact, I wouldn't be surprised if this situation is the cause of the intermittent poor reception you've seen on 900MHz. For models with a single 900MHz antenna, best practice is to orient it -- and the 900MHz transmitter antenna -- vertically. On RCGroups, in the X20 thread, there's a fellow called JohnWilliamson who is an extreme advocate for using a vertically polarized external 900MHz antenna with the X20. That advice seems sound to me. However, I don't find myself in agreement with everything he advocates, or with the tenor of some posts.
- The 2.4GHz antennas in the model are enclosed in black 'straws'. Many materials including some plastics can degrade 2.4GHz reception. Black materials can be especially problematic if the colour results from carbon. Are your straws a big problem? My guess is probably not. Lots of pilots enclose receiver antennas in various materials without noticeable impact. Personally, I always expose at least the active end of a receiver antenna.
One other thing to look into is range testing. More specifically, a range test of the model in only one orientation is of limited benefit. It's better to walk a slow circle around the model at about 30m distance. That approach can reveal specific orientations in which reception is weak. With one single-antenna 900MHz setup I tested, I encountered several orientations in which reception was lost entirely. Even better than a 'walkaround' range test would be a one that accounts for all possible orientations of the model in the three dimensions. However, that's not easy to accomplish.
Apologies for the very long post.
P.S. The log graph I posted was made with
EdgeTX Companion. That program is designed for use with the EdgeTX operating system, but as you saw, it can also be used to analyze logs from EthOS. It's waaaaay easier than using a speadsheet.
