[SOLVED] Taranis X9E + X6R, random telemetry losses

[Pax1601]

Hello everyone,

I recently got a new Taranis X9E, a QX7, and two X6R receivers. The radio operates very well and I'm very satisfied, the RSSI meter is at half scale even when the airplane is almost at the maximum range at which I can fly it. The only problem I've experienced is a set of very random drops of the RSSI meter, with the related "No telemetry" calls. It first happened during its first fly a week or so ago, and ammitedly the plane was on my right and not in front of me, such that maybe the radio signal was low. I ignored the problem, and went on. Today, after more than 1 hour of total flight with no problems whatsoever, it happened again many times, at different locations, also when I was directly pointing at it. When I landed, it did it an other couple of times, with the plane some 10 meters in front of me, on the ground. I disassembled the plane, checked for loose connections and similar things, and found nothing. I flew again with no problems, and I checked the RSSI meter in the same position as before, reading a value of almost 90.

When airborne, to my impression, I've never lost control of the plane, even if the RSSI meter went to 0. The bird is quite gentle in its flight however, and I may have not noticed it. I've read online that these symptoms may be associated with bad antennae placement and interference, so I decided to ask here for help. Attached you find a set of photos of the plane. It was originally an electric sailplane, which was then converted to nitro, then converted to electric again, and received a steerable landing gear. I'm using it to learn using a master/slave system, my dad uses the X9E as master while I use the QX7, and it flies quite nicely. Clearly, the transmitting X9E is always pointed at the plane.

What I find odd is that I would assume that bad antennae placement should cause this type of problem more "uniformly" in time, while it appeared that problems happened very close to each other.

I was wondering is if the transmission power of the TX is different from that of the RX. The receiver is powered by the 5.5V coming out of the BEC. I've tested the output under high servo load and it is quite stable so to my knowledge there appears to be no power loss. The telemetry losses however do not appear to be caused by low transmission power because they also happened with the plane close to the TX, like 10 meters, in a condition where the RSSI would read almost 90, then suddently go to 0, then 90 again. Is it possibile that local interference from other radio signals may affect the telemetry feedback more than the control uplink? Also because many of these RSSI warnings happened in the span of 2 minutes, and then nothing for 10 minutes or so, while we did not power anything off.

What I would like to understand is what may cause such temporary losses and if those are dangerous or not, indicating a possible malfunctioning of the radio set. Also because random unharmful RSSI warnings may cause us to ignore them, until the day that the warning is real. You know, the boy who cryied wolf...

This is the first set of 2.4GHz radio sets that we use so we are quite new to them, I ask you help for trouble shooting, please be patient if we made some rookie mistakes

Thank you!

Davide

[jhsa]

I'm not saying that this is the cause of the low RSSI but DO NOT point the tip of the antenna at the model.
Antennas radiate from the side, not the tip. Pointing the tip at the model could greatly reduce the range..

João

Sent from my thor using Tapatalk

[Pax1601]

I'm not saying that this is the cause of the low RSSI but DO NOT point the tip of the antenna at the model.
Antennas radiate from the side, not the tip. Pointing the tip at the model could greatly reduce the range..

João

Sent from my thor using Tapatalk

Thank you for your help

Yes since the X9E is stock and has the antenna to the side, when I point the radio to the model it means that the antenna is actually perpendicular to the radio path Indeed I get good RSSI values at long range, way above the critical values.

[jhsa]

Ok. I have just said that because you said you come from the older radio system.. We used to point the tip of the antenna at the model back then

João

Sent from my thor using Tapatalk

[MikeB]

How are the antennae placed in the aircraft? Normally they should be at rightangles to each other. I usually mount mine so 1 is horizontal, fore and aft and the other is vertical. (Note, the part that matters is the unscreened part, about 30mm long, at the end, or the "paddle" if you have that type).

Mike.

[Pax1601]

Thank you both for your help

I have attached pictures of the antennae in the first post, I don't know if you can see them
The antennae are pointing out of the fuselage, at 90 degrees from each other, and are horizontal

Davide

[jhsa]

Ok, they look both horizontal to me, but even that should be fine as the plane seems to be a glider?
If that is the case, your radio's antenna should be horizontal to one side.
But even that antenna placement should not give you telemetry loss at 10 meters. I have seen that happening long long time ago if I well remember, but it was fixed. I don't use openTX trhough. I use Ersky9x on my radios..

João

[Pax1601]

Ok, they look both horizontal to me, but even that should be fine as the plane seems to be a glider?
If that is the case, your radio's antenna should be horizontal to one side.
But even that antenna placement should not give you telemetry loss at 10 meters. I have seen that happening long long time ago if I well remember, but it was fixed. I don't use openTX trhough. I use Ersky9x on my radios..

João

Thank you very much for your help.
Yes the plane is basically a glider, no strange manoeuvering whatsoever
I should notice that both the transmitter and the receiver have stock firmware in them. The X9E has opentx 2.1.6 which dates back to december 2015.

Davide

[Carbo]

I am very satisfied with my X9E / X8R combo. X6R should have the same performance. Only some S6R have/had telemetry lost issues.

As your RSSI is fine (but please add a logfile with RSSI here), it is presumably not an antenna thing. Did you swap the RX, to see, if the other RX has the same issue?

Here is a perfect overview for you, what you can expect from your system:

https://opentx.gitbooks.io/manual-for-o ... alues.html

[Pax1601]

I am very satisfied with my X9E / X8R combo. X6R should have the same performance. Only some S6R have/had telemetry lost issues.

As your RSSI is fine (but please add a logfile with RSSI here), it is presumably not an antenna thing. Did you swap the RX, to see, if the other RX has the same issue?

Here is a perfect overview for you, what you can expect from your system:

Thank you for your help

I am also very satisfied with the overall performance of the system, if not for this small issue. I still have to try with the other RX, and also with the other TX. Luckily I have two TXs and two RXs so I should track down the culprit. I will enable logging and post the log files as soon as I'm able to get back to the field, very bad weather in Italy right now

Do you guys have any idea what might be the problem? In particular, do you think it is more probable that the problem is in the TX or the RX? I know it is very few info, but I was wondering if know issues may cause this problem. For example, the fact that telemetry losses happened very close in time, something like 2 minutes, and then stopped made me think it may have been some local interference of some kind. Is this a plausible hypothesis or this type of radio link is too robust for this to happen?

Thank you again for your help,

Davide

[Pax1601]

I'm back with some data.

I've performed a series of test, sadly not in flight due to strong winds. Attached you find two log files I got:

- log_1.png represents the RSSI in dB with normal operation. The model was sitting some 5 meters in front of me, in my living room, and I tried wiggling and moving every cable and connector in the plane itself. I also tried moving the plane around to find shadows or similar. As you can see, the radio signal is quite stable, fluctuations are caused by me moving in front of the radio or covering the antenna with my hands. I also tried moving the servos, to see if it made any difference. I tried to see if the RX got hot due to intense servo movements or if the BEC output voltage would drop due to excessive amp draining, but the RX remained nice and cool and the output voltage was always in the 5.4-5.6V range.

- log_2.png represents the RSSI in dB during two consecutive range checks. In both range checks, with the radio in range check mode, I got below 45dB at 38/39 meters from the RX. Also notice that the test was not performed in optimal conditions, as the plane was on the ground, sorrounded by buildings. It is however my understanding that a distance of 30m should be acceptable.

Both the RX and the TX stayed on for a total of around 50 minutes, during which the radio signal was never lost, apart from when I turned the RX off for a brief moment to install the wing.

What I understand from this test is that it appears that the radio signal lost problem is caused either by:
- rare and intermittend RX/TX failures, which I could not replicate;
- failures due to the specific operating environment in flight, like vibrations, heat from the ESC and similar, which again I could not replicate;
- local interferences at the field.

This is all I could do without actually flying the bird. Can you understand something more from this data than me? Does it look ok to you? I'm in your hands.

P.S. surely I will proceed to test the system swapping TXs and RXs but first I must be able to replicate the issue otherwise I will never know if the problem is solved.

Davide

[MikeB]

It all looks OK to me.
There are 2 reasons you could get the RSSI low indication. One is the Rx really isn't receiving a good signal. The other is the Tx didn't receive the telemetry data from the Rx. While the Rx has two antennae, it is believed that only one is used for transmission of the telemetry data.
It is therefore more likely you could have the Rx transmission comming from an antenna that is pointing directly at the Tx.

Mike.

[Carbo]

What I understand from this test is that it appears that the radio signal lost problem is caused either by:
- rare and intermittend RX/TX failures, which I could not replicate;
- failures due to the specific operating environment in flight, like vibrations, heat from the ESC and similar, which again I could not replicate;
- local interferences at the field.

Are you sure you lost radio signal (uplink TX --> RX), or did you loose only telemetry (downlink RX --> TX)? You wrote in your first post, you did never loose control, this implies, that you lost only telemetry = downlink. This is mostly RX related. Therefore it is a good start, to try with another RX.

Your rangetest shows normal behaviour. I get RSSI 50 in 30m distance in optimal conditions, RX and TX at least 1m above ground. Your RSSI is good for 1km in flight.

There is a chance, that your RF firmware in your TX and in your RX is the first "EU" - version from 12/2015. It was followed by the "LBT" firmware, also made for EU, but with better performance. It is a good idea, to update TX (XJT) Modul and RX to the newest LBT firmware. Unfortunately there is no chance to read out the actual firmware versions. But please read the update instructions carefully, watch some newer videos and only start to update, when you are sure, you understood the procedure. There is also a good chance to open a can of worms, when you are new to this. Search for "Update SPort devices, update FrSky XJT, update FrSky X6R/X8R". Send me a PM and i will guide you through, if you want. Or you search for an experienced user around your home. The beginnings were hard for the most of us

Nothing to do with your issue, but you should know: unfortunately with your TX from 12/2015 there is another chance, that your 2.1.6 FrSky bootloader is faulty (2.1.6 OpenTX is fine) and you have no access from Companion to your transmitter. If you realise this, then update OpenTX and bootloader to 2.1.9 or immediately to 2.2.0. This is completely independent from RF firmware in your TX (XJT) and RX. There are 3 independent firmwares in your TX:

- XJT Modul firmware (RF)
- bootloader
- OS (OpenTX or alternatives)

If you walked through this, you will get a (nearly ) perfect system.
It is only the 2015 versions with this issues, later produced hardware is fine.

[jhsa]

While the Rx has two antennae, it is believed that only one is used for transmission of the telemetry data.
Mike.

That being the case would mean that the receiver has no diversity and it would be really a shame..
The D8R-II Plus for example receives and transmits using both antennas.
Before that, Frsky was selling the old D8R as a diversity receiver.. That was not true.. One of the antennas only transmitted telemetry while the other only received the signal to control the model.. When I found that out (quite recently) it explained why I was having low RSSI warnings sometimes. Some of them might have even been due to a bad placement of the receiving antenna, or when it got blocked by some parts of the model.. But I did believe the RX had diversity

I'm not saying that this is the case now, but it's worth checking..
I believe that specially with the "X" protocol a diversity receiver is a must..

João

[MikeB]

Receive on both, but (maybe) only Tx on one, so still diversity on receive.

Mike.

[Pax1601]

Thank you all for your help!!!

So, to answer a couple of questions:
- the website I bought the radio says it is LBT. The second X6R that I have has "EU LBT" printed on it (the other was inside the X9E case) and indeed it connects to the X9E, so I would assume all TXs and RXs are LBT;
- I have to say that my impression is that I never lost control of the plane. It was quite windy and I was fighting with my ailerons, and it appeared to me that they were always responsive. The bird flies gently and the failsafe is set on "Hold" so I would not say with 100% confidence that I did not lost control, but that appears to be the case to me;
- I will definitely consider updating the firmwares and this afternoon I will test if Companion works or not, thank you for your help and you kindness!

To answer the other diversity related questions, I just performed an interesting test. I put the radio in range check mode, and alternatively covered one or both antennae. What I found out is that I never lost telemetry even when the RSSI went to 10-20 values, as I assume that the transmission power of the receiver is not affected by the range test mode. However, I noticed that while covering one antenna with my hand, the RSSI would drop by 10-15dB or more, while absolutely no change whatsover was detected while covering the other. It appears to me that either:
- only one antenna receives the control link from the radio;
- the RSSI value is computed from one antenna only.

I performed the same test with the other X6R and obtained the exact same results. In the second case, it may happen that the radio detects low RSSI even if the uplink is still good?

What I find odd in my case is the fact that all "incidents" happened very close in time, like 4-5 times in 2 minutes, and then nothing, completely gone. I would induce from that that either:
- the problem is not related with bad antennae placement, as I would assume I would get warnings all the time, or at least more uniformely in time;
- the problem may be caused by some particular factor, like interference, heat, vibrations, or something else, that triggered the "failure" and then went away.

What do you think in that regard?

Thank you again for your kind help!

Davide

[jhsa]

Receive on both, but (maybe) only Tx on one, so still diversity on receive.

Mike.

At least the old D8R, as far as my testing (while comparing it to the DIY receiver) went, it didn't receive on both.. Actually that should be easy to test.. Just have to remove one antenna at the time and see what happens..
As a curiosity, and when I have time, will do it again just to make sure I'm not telling lies here
I do find very strange that it receives on both but only transmits on one actually..

João

[Carbo]

- I will definitely consider updating the firmwares

The first LBT fimware is still OK, an update is not urgent. The newer RX firmware prevents RX lockouts with faulty ignitions. It is your choice, i am still happy with the first one.

[MikeB]

Just have to remove one antenna at the time and see what happens..

Not a good idea, the Rx transmits telemetry data, so you might damage the transmitting circuitry with no antenna fitted.

Mike.

[bob195558]

May be able to cover one antenna up at a time with a metal shield or something ?

[jhsa]

Just have to remove one antenna at the time and see what happens..

Not a good idea, the Rx transmits telemetry data, so you might damage the transmitting circuitry with no antenna fitted.

Mike.

Yeah, you're right.. I will find a way.. I remember testing it at 1.5Km. That was when I found out that only one antenna received.. Maybe I should do that test again while it is not raining..

João

[bob195558]

Could scope it too ?

[jhsa]

How would you scope it??

João

[bob195558]

Connect your oscilloscope to the antenna wire.

[jhsa]

Oh, errr.... can your scope read 2.4Ghz signals? Mine is only good for about 100Mhz I guess..You see, it is an ancient scope.. From the 70's..

Let me ask something, did you ever work with a scope?

João

[bob195558]

Yes, and I have one, but have worked very little with oscilloscopes.
What I have is one of those PC-Oscilloscope that uses the very slow USB-2 connection and junkey software.
It is not very good.

[jhsa]

I might just need a simple range test (in range test mode). I don't think I need the 1.5Km test for it.

Will try to do one in the next days..

João

[Kilrah]

An oscilloscope that can scope a 2.4GHz signal costs about as much as a house, and just the probe to connect it to the circuit is a nice car... so no

There are low cost spectrum analyzers that are much more fit for the purpose though, e.g. RFExplorer.

[bob195558]

I have the RF-Explorer 6G Combo (http://rfexplorer.com/models/), but I have no idear how I could use it to
see which antenna of a FrSky receiver is sending telemetry and/or receiving the RF signal from the XJT module.
I normally use the the software "RF Explorer Windows Client" (http://rfexplorer.com/downloads/) on my laptop
that comes with this spectrum analyzer.

Bob B.

[jhsa]

Well, I am the one wanting to make this simple test..
As I'm not going to sell my house or my car to buy an oscilloscope and a cable for it I will do a simple range check which is much cheaper, and probably more effective

João