G-RX8 range/signal issues?

[nhedler]

Hello!

I fly a Phoenix V2 with a G-RX8, and my dad just got another with an X8R (with the new RX firmware, super cool!). We are seeing two different RF behaviors, and I'm not sure where the issue lies.

The first issue is that my dad's X8R is giving spurious RSSI warnings (when flown with an X9-Lite); I am fairly sure that I read something about the UNI firmware giving RSSI values in a different range than stock, and that the warning thresholds can be lowered as long as telemetry comes back and there's no LOC. From what we've been able to tell so far, there hasn't been any LOC on his plane, so I believe the issue is just that the warnings are triggered too early.

The bigger issue is that my G-RX8 (from an X9D+, non ACCESS) sometimes triggers failsafe momentarily without any RSSI warning; all of a sudden, the plane will abruptly pitch-up (result of FS settings) and warn "telemetry lost" before regaining link. My antennas are placed with one toward the tail (chordwise horizontal polarization) and one in front of the wing, taped inside the fuselage (vertical polarization) in the hope that the aluminum tube wing spars won't cause too many issues as they might with an antenna with spanwise horizontal polarization. The LOC mostly occurs when the plane is less than about 30 deg off the horizon and I believe it is more common when flying toward myself (not necessarily directly *at*, just in my general direction).

I understand that the G-RX8 had some teething issues (IIRC there was a batch with an incorrect SMD component, capacitor swapped with a resistor?) which may also be in play here, and I can't rule out RF noise.

 

[Wayne]

UNI is fine on the same RSSI levels as the normal FrSky firmware. We spent a lot of time to get this refined and closely matched as we did not want people to have to adjust this important value. (The FrSky ACCESS protocol has a different RSSI scale.)

With UNI, please discover NEW SENSORS and you will now have VFR. Monitor the VFR as it will tell you more about the quality of the RF connection than just RSSI. VFR is calculated with RSSI value and the quality of the packets that are being received. You could have perfect RSSI and no good packets.

The G-RX8 with that resistor issues should be very rare. Probably less than 1% of total units out there. It was a long time ago, and was caught pretty early on. But possible. As I recall those had very poor range and junky RSSI. I may be remembering wrong.

Since you are getting the "telemetry lost" warning, I do think you have a range issue. You should be able to test this on the ground with range check mode and trying different antenna configurations. Try swapping to another receiver and see if the range check is any better. Sometimes it is just a bad receiver. If the other receiver does better, then take a close look at the antennas. Near the crimp where it connects to the receiver we will see issues here.. It is a stress point on the antennas. Any wire visible at this crimp is a sign of failure, time to replace.

Do some range check tests and let us know what you find.

Another possible issue is the ESC, sometimes ARFs come with some hot garbage for an ESC. We have seen more than a few that put out so much noise they block the receiver from doing its job. (I think some ARFs do this on purpose to sell more airframes...)

 

[nhedler]

From what we can tell, my dad's UNI rx doesn't appear to lose link even when RSSI is very low; we changed the thresholds to 35 and 30 and had no noticeable issues. I didn't get a chance to watch his VFR while flying, but intend to check next flight. In range-check mode, I get values that vary wildly even without moving. I will check the antenna connections, but they'd been replaced recently, so I'd hope I'm not so clumsy to have damaged them already.

I'm considering rearranging things so that I can mount an rx in the V-stab instead to get better separation between antennas and other potential sources of RFI, but that'll mean getting an external vario.

 

[Wayne]

Unless you have a ton of metal or carbon fiber in the plane, I do not think this is the issue. Just do not tape your antennas to anything metal or carbon, and do not let them touch those materials. I try to stay away from the ESC and LIPO packs when possible.

Lowering your RSSI threshold is not a solution. While it will turn off the alarms, it is not fixing anything, you are still at risk. Turning down the RSSI values is like removing the siren from a smoke detector.

Your radios has data logging, turn it on, and study the results. It will write the data to the SD card, and you can look at it with a spread sheet program. If the VFR on the UNI is staying high, then pretty safe to say the transmitter is fine, and your other receiver has some sort of issue. Might be time to replace it just to be safe.

 

[nhedler]

My antenna placement options are unfortunately limited by the antenna length, and the vertical antenna is pretty close to battery and ESC, so I believe that's contributed to the LOCs. I'm using a Neuron S, so hopefully it's not contributing too much to the issue.

The change of thresholds was a temporary measure while testing for LOCs, and I set up a display item for minimum VFR as a quick at-a-glance check. I had forgotten about data logging, so I'll look into that.

We have been using different transmitters, so I'll also try out the dual-bind feature on my dad's RX and see what happens with my TX compared to his.