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TX16/ R88 Low RF - Am I doing something wrong?


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22 hours ago, Mike Blandford said:

I just ran a few tests using a FrSky D8R-PLUS (FrSky D8 mode):

X9D+ with DJT module gives RSSI over 100 at 5 feet.

9XR-PRO with XJT module in D8 mode gives RSSI over 100 at 5 feet.

TX16S with internal MPM in FrSky D8 mode gives RSSI around 85 at 5 feet. (Yes it was fine tuned).

A couple of external MPMs in FrSky D8 mode give RSSI around 100 at 5 feet.

 

I've always suspected the MPM gives lower output power, than FrSky modules, when using the CC2500 RF chip. I have several MPMs and they all show lower RSSI, some more than others, with, in my case, the internal module of the TX16S the lowest.

 

Every 3db lower reduces the range by 30%, 15db down would reduce the range to one sixth.

 

Mike

Mike, thank you for this, I really appreciate this input.

 

Can you answer a few questions I have so I know exactly what I'm doing?

 

Does the XJT module fit the TX16S?

If not, which modules do fit, and will talk to my frSky and Radiomaster R88 receivers?

If I use an external module, I presume everything works the same as with the internal module?

 

Thanks Mike

 

Graham

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  • 2 weeks later...

Update:

 

Thanks to Jake Bullit, I now have a genuine FrSky XJT module. My reasoning for adding this was based on Mike Blandford's report of potentially weak signal from the CC2500 based chipset internal Radiomaster MPM module. Having never seen an RSSi figure better than at most 90dB, this tended to corroborate Mike's findings. The hope would then be that the XJT module would improve the RSSi figure in an exact like for like situation. Whilst this is at best a comparative test, it would at least demonstrate an improvement.

 

Having tried the XJT, here's what I know...

 

I haven't yet been able to do a direct A/B comparison with a brand new genuine FrSky X8R receiver. I can't bind to the XJT module, which I suspect may be a firmware thing. I will update the XJT firmware and try again later.

 

However, I Was able to do an A/B with a radiomaster R88. Whilst this may not be the best receiver from an absolute range point of view, the fact that I could reasonably quickly swap between internal and external module without affecting the orientation or distance between TX and RX once again gave me a comparative test. And here's the kicker...

 

I get a better RSSi result from the internal MPM than I do with the XJT. This is the worse possible outcome to me, as it is utterly inconclusive. I am now back to square one.

 

There is one tiny bit of evidence that may be a lifeline towards diagnosis. I'm yet to thoroughly investigate this, but on an occasion where I rebound the X8R to the internal MPM, after creating a connection, the radio briefly reported telemetry lost, and the green light went out. It looked like the power dropped (quite possible as I was using old switchgear and NiMH pack for the sake of testing). However, usually when I turn off the receiver, the telemetry lost report takes a few seconds to report, so there may be something else happening in the RF or telemetry link. This opens up point 1 below...

  • Is the RSSi figure a total red herring and the problem is somewhere else?
  • Would I have the same issue with the XJT?
  • I still have very little confidence in my gear
  • I will finish a 1/6th scale spitfire in a few moths, and there is no chance I'm committing aviation unless I find a way to restore confidence.

I'm not too sure how to get out of this. I could simply replace the gear, but what with? If I retain the receivers, am I going to do any better? If I swap brands, that's a lot of money. If I stick with what I have and break another airframe, that's also a lot of money...

 

Do I make a sacrificial model and simply fly until I have tested all my receivers and rebuilt my confidence? Trouble with that is, if I get one single failure, I'm back to square one. But until I can find a smoking gun, I don't see that I'm ever going to trust this otherwise excellent radio.

 

Can anyone suggest a way out? Or a therapy group? Or maybe a new bourbon to try...

 

Graham

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36 minutes ago, Graham Davies 3 said:

Update:

 

Thanks to Jake Bullit, I now have a genuine FrSky XJT module. My reasoning for adding this was based on Mike Blandford's report of potentially weak signal from the CC2500 based chipset internal Radiomaster MPM module. Having never seen an RSSi figure better than at most 90dB, this tended to corroborate Mike's findings. The hope would then be that the XJT module would improve the RSSi figure in an exact like for like situation. Whilst this is at best a comparative test, it would at least demonstrate an improvement.

 

Having tried the XJT, here's what I know...

 

I haven't yet been able to do a direct A/B comparison with a brand new genuine FrSky X8R receiver. I can't bind to the XJT module, which I suspect may be a firmware thing. I will update the XJT firmware and try again later.

 

However, I Was able to do an A/B with a radiomaster R88. Whilst this may not be the best receiver from an absolute range point of view, the fact that I could reasonably quickly swap between internal and external module without affecting the orientation or distance between TX and RX once again gave me a comparative test. And here's the kicker...

 

I get a better RSSi result from the internal MPM than I do with the XJT. This is the worse possible outcome to me, as it is utterly inconclusive. I am now back to square one.

 

There is one tiny bit of evidence that may be a lifeline towards diagnosis. I'm yet to thoroughly investigate this, but on an occasion where I rebound the X8R to the internal MPM, after creating a connection, the radio briefly reported telemetry lost, and the green light went out. It looked like the power dropped (quite possible as I was using old switchgear and NiMH pack for the sake of testing). However, usually when I turn off the receiver, the telemetry lost report takes a few seconds to report, so there may be something else happening in the RF or telemetry link. This opens up point 1 below...

  • Is the RSSi figure a total red herring and the problem is somewhere else?
  • Would I have the same issue with the XJT?
  • I still have very little confidence in my gear
  • I will finish a 1/6th scale spitfire in a few moths, and there is no chance I'm committing aviation unless I find a way to restore confidence.

I'm not too sure how to get out of this. I could simply replace the gear, but what with? If I retain the receivers, am I going to do any better? If I swap brands, that's a lot of money. If I stick with what I have and break another airframe, that's also a lot of money...

 

Do I make a sacrificial model and simply fly until I have tested all my receivers and rebuilt my confidence? Trouble with that is, if I get one single failure, I'm back to square one. But until I can find a smoking gun, I don't see that I'm ever going to trust this otherwise excellent radio.

 

Can anyone suggest a way out? Or a therapy group? Or maybe a new bourbon to try...

 

Graham

I can't recommend Bourbon to fix your issues, but I can recommend you invest in a 7c Lemon telemetry receiver, I find them very reliable, great range and lots of telemetry functions to keep you informed on what is going on. Cheap too. Almost too cheap but they are good.

I suggest you get one and put it in a lightweight foamy and fly and fly, hopefully you will gain confidence in the stup and move onto the models you really want to fly.

I'm using Radiomaster TX16s MK1 by the way.

Edited by Outrunner
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Graham,

 

A couple of points that are perhaps worth thinking about:

 

Using the XJT module in your Radiomaster transmitter will completely eliminate the entire RF section of that transmitter from the equation. Assuming that Jake (its original owner) never had issues with that module then you should have some confidence that the module itself is alright. Which really leaves your receivers.

 

If your X8R won't bind with the XJT then there is probably a version or mode difference. You could flash your X8R with the UNI firmware, this will allow it to bind with the X8R irrespective of the version or mode. Then you could compare the results obtained between the different makes of receiver.

 

In addition, the XJT will fit any transmitter with a JR style module slot in the back, such as Taranis etc. Perhaps you could try somebody else's transmitter with your module and both makes of receiver, though I wouldn't have thought that the tx itself would be relevant if you aren't using its RF section.

 

Also, rather than a sacrifical model, could you install your test receiver and battery into a model that has its own transmitter, receiver and servos etc., then fly the model normally (or get someone else to) whilst monitoring your Radiomaster tx for loss of telemetry signal. Just a normal trainer or something. Your receiver won't be controlling anything.

 

Brian.

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The problem with the Radiomaster receivers appears to be that they need to have the transmitter tuned to each specific receiver to compensate for poor quality components and/or poor QC. You can do this with the MPM but not a genuine FrSky module as there is no need for this with proper FrSky receivers. With up to date firmware and a FrSky receiver on matching firmware you will almost certainly get very good range. With a Radiomaster, who knows? It might be a decent match, it might not. My FrSky stuff all works very well. The Radiomaster receivers have long threads full of complaints and problems over on RC Groups where the they appear to have come to the conclusion that some of them are fine, while others are not. Personally, I don't feel this inspires confidence.

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Thank you all for your input. A few things:

 

Outrunner, thanks for this, but whilst I acknowledge the R88s are not the best, I have had issues with 3 different receivers. I don't believe in coincidences; the common denominator is the transmitter. Other receivers may be less sensitive to the issue, but the issue remains.

 

John, Yes I'm aware of this. All the clone receivers have been fine tuned to within an inch of their lives. But as above, the problem appears to lie with the transmitter, and specifically the RF section.

 

Brian, yes, some good advice and comments. I agree that the module takes the RF section entirely out of the equation. Whilst I could use this and take advantage of Jake's previously reliable RF link, the reported low RF still concerns me. Whilst it may be that I have some other (probably intermittent) issue with the internal RF, the low reported RF may or may not be a problem. If it isn't, it makes a bit of a nonsense of RSSi telemetry as I can't draw any conclusions from it! It's not a bad idea to 'fly' the gear in a model with another control link, but this is a very variable test. I was really hoping to just buy some gear and use it! I accept that Radiomaster is a 'budget' brand, but it was still £300, so would hope it had the primary function covered. Not that I'm knocking the brand; we all don't need to go there without really knowing what is happening.

 

Graham

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Graham, you have not tuned a receiver, you have tuned your transmitter to match each receiver. As it isn't possible to do this with a FrSky tx or module the receiver's performance may well be affected. I believe Radiomaster receivers are only suitable for use with MPM based transmitters which include the fine tuning ability. Your only valid test will be to try the X8R receiver with the FrSky module and compare it against the X8R with the Radiomaster's internal module. That will give you a true indication of relative tx performance. The Radiomaster receivers can't tell you anything because they almost certainly won't work well with the FrSky module.

(P.S. dump the Bourbon and try a nice Speyside malt. That fixes everything. For a while)

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5 hours ago, John Muir said:

The problem with the Radiomaster receivers appears to be that they need to have the transmitter tuned to each specific receiver to compensate for poor quality components and/or poor QC. You can do this with the MPM but not a genuine FrSky module as there is no need for this with proper FrSky receivers. With up to date firmware and a FrSky receiver on matching firmware you will almost certainly get very good range. With a Radiomaster, who knows? It might be a decent match, it might not. My FrSky stuff all works very well. The Radiomaster receivers have long threads full of complaints and problems over on RC Groups where the they appear to have come to the conclusion that some of them are fine, while others are not. Personally, I don't feel this inspires confidence.

 

I believe you tune it once when binding to a specific receiver, then you can use this tuning all receivers of that type.......

 

Irrespective of that, I have given up on fretting about RSSI values and just do range checks the old-fashioned way.  In about 2,500 flights with lots of different brands of receiver, I have had no issues.

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I agree GG. I range test on reduced power and walk until the controls stop working. That's usually well over 80 paces with FrSky gear. I check the RSSI at that point and reckon that should be my 'Oh No' number. It's generally at about 30. The default warning values usually work fine in flight but I do have one receiver that reports RSSI values consistently about 10 less than the others, so I reduced the RSSI alarms for that one to avoid being annoyed by that lady in the box when I'm flying. The range is not an issue, just the RSSI calibration is different. Going by RSSI numbers alone as a guide to range is pointless.

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3 hours ago, John Muir said:

I agree GG. I range test on reduced power and walk until the controls stop working. That's usually well over 80 paces with FrSky gear. I check the RSSI at that point and reckon that should be my 'Oh No' number. It's generally at about 30. The default warning values usually work fine in flight but I do have one receiver that reports RSSI values consistently about 10 less than the others, so I reduced the RSSI alarms for that one to avoid being annoyed by that lady in the box when I'm flying. The range is not an issue, just the RSSI calibration is different. Going by RSSI numbers alone as a guide to range is pointless.

Here, you have nailed the issue...

 

I completely agree regarding the RSSi 'crying wolf'. This is my first telemetry set, so was aware of the 'too much information' issue. HOWEVER, and this is the big BUT; I can get nowhere near 80 paces. I get a bit over 30 paces. That never seemed like a comfortable safety margin. I mean, how calibrated is a british standard 'pace'? This is my concern, and has been since the start of this thread. The range seems low.

 

I will try to get out and do a range test with the XJT module, although that may not be for a while

 

Graham

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9 hours ago, Graham Davies 3 said:

I mean, how calibrated is a british standard 'pace'?

I would have thought the positioning and orientation of the model would have a far greater impact on link reliability. Is it lying on long wet grass on the ground or is it 80cm's up on a table?

Edited by FlyinFlynn
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Thanks FF,

 

In the air, and then in a field somewhere nearby...

 

I have had the system over a year and conducted hundreds of range tests. I think we can rule out range checking technique!

 

Going back to the start of the post, I had range issues, and have spent a lot of time optimising antenna orientation, etc. These issues have never been fully resolved and recent failsafes/ crashes have brought this to a head. The problem has manifest in at least 3 receivers, in numerous installations, and resulted in several failsafe triggers. One of these brought down a model, another led to a forced landing that did some damage.

 

I had hoped that I was doing something dumb, as that is certainly within my capabilities! 

 

Graham

 

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RSSI is useful, but only once you've established what is 'normal'. I always check my logs when I go home and if the RSSI plot looks similar to the last time I flew that plane, I'm happy. Any obvious differences mean something's wrong. And it does give an indication of flying too far away providing the warning level is sensible. I just don't get any warnings in practice.

30 paces (however long your legs) is marginal and I would consider totally inadequate for a FrSky receiver, but I don't know what should be expected of a Radiomaster receiver. If it is the transmitter restricting the range, i.e. if the X8R has less range when tested with the MPM than with the FrSky module, then I would give up on it or switch to Spektrum or Lemon receivers which use a different chip to FrSky. Of course there is the possibility that the tx is simply faulty and is transmitting at reduced power across the board, but the only way to find that out would be to range test with a different protocol and see if the problem persists.

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On 10/12/2023 at 11:42, John Muir said:

The problem with the Radiomaster receivers appears to be that they need to have the transmitter tuned to each specific receiver to compensate for poor quality components and/or poor QC. You can do this with the MPM but not a genuine FrSky module as there is no need for this with proper FrSky receivers. With up to date firmware and a FrSky receiver on matching firmware you will almost certainly get very good range. With a Radiomaster, who knows? It might be a decent match, it might not. My FrSky stuff all works very well. The Radiomaster receivers have long threads full of complaints and problems over on RC Groups where the they appear to have come to the conclusion that some of them are fine, while others are not. Personally, I don't feel this inspires confidence.

 

@Graham Davies 3, based on my testing with those RM RXs using known good TXs and those threads mentioned by John Muir with less than positive feedback(!), the best thing to do here is junk the Radiomaster RXs and focus on identifying whether satisfactory performance can be extracted from your current TX using the XJT and/or internal MPM modules. The best way to do that is to flash the XJT and Frsky RXs to matching firmware, then redo the tests using the same Frsky RX and in D16 mode using both the MPM and the XJT module, comparing range test and RSSI data for both. That will at least tell you if the MPM has a more fundamental issue.

 

If the results are still mixed/inconsistent and you still aren't confident at that point, do some of the tests mentioned by @RottenRow above; they are all good suggestions that will allow you to eliminate one potential point of failure at a time. 

Edited by MattyB
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