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Signal Reliability at McCoy Field - Printable Version

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Signal Reliability at McCoy Field - caffeine - 16-05-2023

In light of the RF signal issues some people have reported at McCoy field, I had a look at the telemetry logs of my last couple of flights there.

I'm using ELRS at the 100Hz packet rate, using 10mW transmitter power (this is the lowest TX power setting on my internal ELRS module on my TX16S transmitter)

ExpressLRS recommends a minimum signal sensitivity limit of -108dBm for 100Hz.

In my flights there (including flying at the same time as Stephen with his ELRS system) my telemetry reported RSSI level (1RSS, as I have a single antenna ELRS receiver) never got below -85dBm. This is the RSSI level reported by the receiver. I also log TRSS, which is the telemetry RSSI reported by the transmitter, but it's also not anywhere close to the minimum.

The other measured value i looked at was LQI - Link Quality Indicator) which represents the proportion of messages cleanly received. This got down to a minimum of 94% on one flight, but generally was in the 97-100% range. At 100Hz packet rate, a packet or two missing every now and then is not an issue.

   

Long story short: In my experience, ELRS appears to be unaffected by any interference or link quality issues at McCoy park.


RE: Signal Reliability at McCoy Field - Doish - 16-05-2023

That’s really interesting.
As you may know I fly using an old Spektrum DX6I.

Would you say this old controller is susceptible to issues / has been known to have issues?

I’m waiting on funds for my Radiomaster hence have just avoided flying for past 6 months


RE: Signal Reliability at McCoy Field - caffeine - 16-05-2023

I have no experience flying other protocols or TX types at McCoy field, so I can't give first hand info, however I've heard anecdotally that people have experiences short interruptions to RF signals, leading to momentary failsafe events.

Not sure if anyone has lost a plane because of it, but it's not very confidence-inspiring.


RE: Signal Reliability at McCoy Field - caffeine - 16-05-2023

Actually, I just checked my radio, 100Hz packet rate has a sensitivity limit of -112 dBm, not -108dBm.

So my -85dBm minimum RSSI is 22 times 'louder' than the minimum limit (dBm is a logarithmic scale, so -85 to -112 is 27dB, which is a factor of 22.4)


RE: Signal Reliability at McCoy Field - greggold - 19-05-2023

I have converted most of my models to elrs rxs now, mostly matek rxs, and 2 models have diversity (2 antenna) rxs. The single antennas work fine, I have had no failsafes at the field, but the dual antennas work better based on    better RSSI and RQly readings, which I monitor. I have dynamic power set to on in the lua setup; on my RM tx16 with internal elrs module used with all my models (except 2) this means mostly the transmitter power is 10 MW, but occasionally with a single antenna rx the power jumps momentarily to 100 mw. This suggests if I did not have dyn power on, there may have been a momentary failsafe. I get notified anytime the power is >25 MW, and I have not had a situation where the power does not immediately drop back to 10 mw.

I also have a RM tx12 tx with an elrs ext module, which I have started to use frequently and I use it with all my elrs models. With dyn power on the usual tx power is 25 mw. The frequency of jumps to 100 mw which only occur with single antenna rxs  is about the same as with my RM tx16, average 1 per flight, with a max of 3 in any flight, and always power returns to 25 within a second.

I have decided to start upgrading my rxs to dual antenna (true diversity) models on the basis of this experience, using mostly matek r24d rxs.  As well as trying to improve the control link in this way, I am trialing a different type of esc (a switching esc) which has been shown to provide a more reliable current to the rx than the usual linear escs which are present on all my models except the one 3S lipo model in the trial. There is a theory which is gaining some currency is that a proportion of control link failures are due to a drop in rx voltage.  This would explain the experience that small 3D models with 2S lipos never have a control link failure, while larger 3S models with the same radio setup have failsafes associated with violent 3D manoeuvres with high motor current. 

The switching esc is

Hobbywing Brushless ESC 40A/40A V2 2-4S Skywalker Speed Controller Drone ESC With BEC/UBEC
https://a.aliexpress.com/_mN1CGdm

The problem with my trial is that now I am having no failsafes its hard to determine if the switching esc is more reliable than my linear escs.

Greg


RE: Signal Reliability at McCoy Field - caffeine - 19-05-2023

I have recently purchased 2 hobbywing flyfun 20A ESCs, these too have switching regulators.

I'm doing it for the size and weight, but also improvement to battery life, as a switching regulator doesn't have the losses associated with linear regulators (on a linear regulator, everything above 5V is turned into heat which is wasted, whereas switching regulators can be upwards of 85% efficient and it doesn't matter (within limits) what the input voltage is)


RE: Signal Reliability at McCoy Field - greggold - 04-06-2023

(19-05-2023, 07:42 PM)caffeine Wrote:  I have recently purchased 2 hobbywing flyfun 20A ESCs, these too have switching regulators.

I'm doing it for the size and weight, but also improvement to battery life, as a switching regulator doesn't have the losses associated with linear regulators (on a linear regulator, everything above 5V is turned into heat which is wasted, whereas switching regulators can be upwards of 85% efficient and it doesn't matter (within limits) what the input voltage is)


I finally got going with data logging on a few models, and now I find I am doing it on all my flights. It is too early to draw many conclusions on issues like radio interference, but there are interesting signals in the data. I have run some graphs and put together a brief analysis on several flights, which I have attached as a pdf.


RE: Signal Reliability at McCoy Field - caffeine - 04-06-2023

Interesting stuff Greg.

Do you know what firmware you were using on the happymodel ELRS receiver?


RE: Signal Reliability at McCoy Field - greggold - 05-06-2023

(04-06-2023, 06:09 PM)caffeine Wrote:  Interesting stuff Greg.

Do you know what firmware you were using on the happymodel ELRS receiver?

On the happymodel diversity rx it is elrs v 3.2.1.

I realise I should have shown what the normal appearance of the plots of the logs looks like. Here is a log of a flight with the Laser which has a matek r24d rx (2 antennas). I have discovered the scatter plots are best done with google docs calc, rather than Libreoffice.

The RSSI in flights with no incident show 1RSSI and 2RSSI measurements moving around but in a similar pattern. The brief periods before launch and after landing show many values above -40 db, and in the air the range is -45 to -70.

The tx power (TPWR blue) remained at 10 mw for the entire flight, over the 5 min for each one of 600 measurements. The RX signal to noise (red) was mostly 11 db, but dropped to 9 for about 10 of the measurements, and to 8 once.

So far most of my flights are like this, with no incident.