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Taranis X9D+ Archer GR6 Access RSSI Low alarms


David Rivers
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 have been flying a carbon Fuselage DLG with an Archer GR6 Access receiver, and I am getting a lot of "low RSSI" and "RSSI critical" alarms. This is usually when the plane is at a good height (80m or more), but also when it is on the ground and more than about 25m away.

Being a full carbon fuse I have been sure to bring the two aerials outside through two holes that I have drilled. The whole of the bare section of each aerial plus about 7-8mm of covered aerial is outside the fuse.

I have not lost control of the model, but I am worried about the alarms. When i look at the logs for a flying session, the RSSI falls as the altitude increases. I thought the range of these receivers was supposed to be about 2km.

I am new to FRSky and this is the first Rx I have used. Am I right to be concerned.

Any help or comments would be appreciated.

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Hi

what are your warning settings

Frsky has this on the download page for Access RX RSSI

 

I also use Frame rate VFR together with RSSI, 

ie if RSSI = <35 and VFR < 90% low alarm

if RSSI = <32 and VFR < 80% critical

 

I have no alerts.... thus far

FIRMWARE
* The suggested ACCESS RSSI is 32 for Critical Alarm and 35 for Low Alarm.
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You may have run your aerials parallel David

But one should run at 90°to the other

Also

Both aerials could come into the shadow of the carbon, coming between you and the receiver for some of the time in flight

So it is preferable to spread those

My own solution are receivers with a satellite receiver 8 inches from the main rx with two more aerials

Edited by Denis Watkins
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  • 1 year later...
On 21/03/2021 at 21:28, Denis Watkins said:

You may have run your aerials parallel David

But one should run at 90°to the other

Also

Both aerials could come into the shadow of the carbon, coming between you and the receiver for some of the time in flight

So it is preferable to spread those

My own solution are receivers with a satellite receiver 8 inches from the main rx with two more aerials

 

Thanks Denis you confirmed my suspicion: my wing is shadowing both rx antennae as I circle. 

 

Below is a plot of altitude and RSSI from a flight in yesterday's FxRES contest in Shrewsbury (where I topped just over 1000 feet 😇).  The regular dips in RSSI pretty much coincide with my cirling.  The steady decline in mean RSSI as altitude increases looks fine but the dips are HUGE - from 56db to 35 db, effectively a 7-fold reduction in received power and almost 3-fold reduction in range (if I have done my sums right).  At 56db the rx is well within range but at 35db it's getting short - as well as annoying hearing repeated verbal warnings from the tx!  The good news is that the valid frame rate only dipped from 100% to 97% in those moments of a few log intervals (0.2sec). 

 

1828955951_2022-07-10PuRESShrewsbury.thumb.jpg.9d2c431fb274d5e7c482cd8f445934dd.jpg

 

Both my antennae exit the fuselage ahead of the wing at 90deg to each other.  They are also well away from the metal pushrods which testing showed also significantly affected signal.  However, in a thermal turn, the banked wing with a CF LE and spar can easily cross the line of sight from tx to rx. I committed the sins of testing the installation with the wing off and conducting pre-flight range checks with the aircraft facing me - both showed good range of course.

 

I don't have a place to put a satellite rx - it's a pod-and-CF boom fuselage with nowhere (obvious at least) to put it.  But I am going to rethink the antenna positions to try to ensure there's always one un-shadowed.  

 

20220704_115628.thumb.jpg.c68fb8b57968b3ddb1c68290f31032cb.jpg

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18 minutes ago, Sussex Pete said:

Yes. And the rx has the latest firmware too 

I had this and Richard at T9 said a batch had been produced with the wrong chip. He replaced mine and the problem was solved but, that was over a year ago. If yours is new it's not going to be the same.

 

Steve

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Am prepared with my crash helmet on, so will fire away.

The whole purpose of licencing microwave transmissions ( 2.4gig ) for domestic use and hobby use was chosen carefully, having first been used by the military.

The frequency set up, requires low power input, is pretty low powered output, and there was a huge advantage that as most households would have one of two (modem/ telephone/ etc etc ) transmitters, there was little to no chance of interferrance. Being Short Range Transmissions.

Typically, a legal set up would be capable of best operation around 800 feet, without multiple fades and drop outs. At 800 feet, a sport plans is not very visible.

Park fly sets are designed and powered for approx 300 feet operation.

Edited by Denis Watkins
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Going by the picture a few posts above both antenna  look to be on the same horizontal plane, this will have both aerials shadowed at the same time they need to be 90 degrees to each other move one to be vertical up or down and your problem should ( will )go away

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2 hours ago, EarlyBird said:

I had this and Richard at T9 said a batch had been produced with the wrong chip. He replaced mine and the problem was solved but, that was over a year ago. If yours is new it's not going to be the same.

 

Steve

Thanks Steve very useful! Not very new I bought them a while ago with projects in mind. I will check with Richard if I don't get this sorted easily 

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2 hours ago, flight1 said:

Going by the picture a few posts above both antenna  look to be on the same horizontal plane, this will have both aerials shadowed at the same time they need to be 90 degrees to each other move one to be vertical up or down and your problem should ( will )go away

I see your thinking. Any pair of lines defines a plane but you're right that the current arrangement puts the antenna plane parallel to the wing and the CF in it (and indeed the CF boom). That was pretty much my first thought too once I saw the log plots. But other people (on FB) tell me they have the same arrangement of antennae and no RSSI problems, pointing fingers at a duff rx (or at least one duff antenna). This will need some testing to sort. This week I hope as the next round is weekend after next! 🙂

Edited by Sussex Pete
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3 hours ago, Denis Watkins said:

....Typically, a legal set up would be capable of best operation around 800 feet, without multiple fades and drop outs. At 800 feet, a sport plans is not very visible.

Park fly sets are designed and powered for approx 300 feet operation.

FrSky expect 1km range in clear air on 100mW output and colleagues who fly F5J get much better range than I am. The rx is sending telemetry back at the same power (but lower frame rate). The tx doesn't record telemetry signal level but I don't see any loss of telemetry data - much as I have not seen a big dip in valid frames getting to the rx. Though I'm not sure of those last points actually tell me anything except I haven't quite gone out of range! :) 

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How is your Tx antenna oriented? If it points almost straight at the 'plane, then it is having the minimum possible signal being sent.

From some testing that was done on the universal ACCST firmware for FrSky receivers, a VFR of 60% is considered a low level, anything above that indicates a good performance. Control was, however, maintained even at a VFR of 10% !

 

Mike

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8 hours ago, Sussex Pete said:

Thanks Steve very useful! Not very new I bought them a while ago with projects in mind. I will check with Richard if I don't get this sorted easily 

The symptoms are exactly the same as I had. With range check there was no loss of control just the low RSSI. If it's the same there is nothing to be done, as I found out after struggling with the alarms for a while. I wish I had checked with Richard first as that would have saved me from considerable frustration.

 

Steve

 

 

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13 hours ago, Mike Blandford said:

How is your Tx antenna oriented? If it points almost straight at the 'plane, then it is having the minimum possible signal being sent.

From some testing that was done on the universal ACCST firmware for FrSky receivers, a VFR of 60% is considered a low level, anything above that indicates a good performance. Control was, however, maintained even at a VFR of 10% !

 

Mike

 

Thanks Mike. I do understand antenna radiation patterns - a physics PhD doesn't wear off too quickly! 🙂  I generally hang my tx from a neck strap and fly facing the model with the tx antenna to one side parallel with the top of the tx so the radiated "donut" is maximal directly in front of me with the donut, rather than the antenna, pointing at the aircraft. 

 

But it's your point about VFR that lit a bulb in my head and suggests a paradigm shift: never mind the tx shouting about the RF signal level, the only question should be, am I receiving good data at the rx

 

In other words ignore RSSI, a value calculated in the rx and hence subject to all sorts of rx hardware assumptions and variabiltity, and concentrate instead on VFR, which is not a calculation but a simple counter of valid data received.  And lo!  And behold!  My VFR remained excellent throughout!  In the air and on the ground, the logged VFR stayed between 92% and 100% all day.  In the flight above with my max altitude and max downwind, VFR stayed at 96% or above and mostly nailed at 100%.  I was receiving good to excellent data despite the RSSI warnings.  

 

17114198_2022-07-10PuRESShrewsburyVFR.thumb.jpg.1f3490ea9b57e244627a342361d1566c.jpg

 

So does this sound like a plan?  Ignore FrSky's generic "suggested" levels of 35dB and 32dB and use ground tests to determine an empirical, rx-specific RSSI at which VFR falls.  Then set the RSSI alarms to a few dB above that.  A bit more effort in setting up each model in exchange for a more reliable set of warnings?  In fact I already have a LS/SF combo reporting high lost frame rates which wasn't triggered at all all day. Perhaps I should have heard that silence over the apparently misleading alarms!

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Thanks to all for your input which helped me think clearly about the problem and its limitations.  And to find the bug in my alarm code that was triggering warnings way too soon! Doh!  

 

But back to the question, Am I receiving good data at the rx?, I have now learned where and when the answer is no and written new alarms for Link Quality low and critical to flag it up.  There's a log tests and results here: Important Firmware Update - ACCESS 2.1.x - Page 31 - RC Groups (p. 31 post #460 ff).  In parcticular, I have adopted voice alarms for my Archer rx, at these values:

 

Link Quality Low: 
VFR Low 75% (can be reached sometimes near the 35dB "floor" zone of the RSSI data) or
RF Signal Low 34db (i.e. once step below a 35dB floor and 1dB below the FrSky advised limit)
 

Link Quality Critical

VFR Critical 65% (reached into the weak zone but some way from link loss) or
RF Signal Critical 30dB (before any sudden decline in VFR and 2dB below the FrSky advised limit)

 

with a half-second allowance for dips while circling.  My feeling is these will give me comfortable warnings to fly closer.  I plan to set the alarm levels for each rx installation separately but expect the numbers to be similar.  

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