Betaflight doesn't show you SNR and that's a problem

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0:00 - SNR is so important. Why doesn't Betaflight show it to you?
0:55 - Recap: what are RSSI dBm and LQ?
2:17 - What's SNR?
3:17 - What even is "noise" anyway?
5:18 - How to see SNR in telemetry
5:56 - How to make Betaflight show you SNR
7:34 - Why SNR is better than RSSI dBm and LQ
8:58 - What is a "bad" SNR threshold?
10:17 - BETAFLIGHT DEVS GIVE US SNR!!!

[@aphinion]

Configured my first quad in BF4.4 now and wondered, why crsf_use_rx_snr didn't work anymore... Turns out they just added the feature and you can now just activate it in OSD! Yep, they listened!

[@DanJonesShow]

One of the ways I used to teach SNR, MER and Error Vector Magnitude was giving one person in my class a piece of paper with a bunch of random 1's and 0's written on it, and another a blank paper with a pen. I would ask the entire room to be quiet and have the one student read to the other the 1's and 0's. The student who wrote it down would read it back and verify there were no "errors". I would give them each new sheets and this time the entire class would make a lot of noise while they did the exact same activity. This demonstrated that there were more "errors" as well as a requirement for the person reading the numbers to raise their voice. In certain digital radios, the transmitter will actually increase its output power to compensate for a noisier environment to try to talk over the noise floor. This is something severely lacking in fpv and model RC is more dynamic radio transmitters. Utilizing a pilot sub carrier like we do in 802.11 protocols to essentially link Tx and Rx using a very narrow, low density channel, could seriously improve link quality at a much further distances imo.

[@Fly_High_FPV]

Crossfire in dynamic power will do this. Keeps cranking power automagically 👌

[@volkergoe]

Expresslrs does this as well.

[@DanJonesShow]

@@Fly_High_FPV But don't you sacrifice latency and packet rate? Rather than locking it in at the beginning of the flight? My vision is to have a system similar to a OFDM/OFDMA Tx/Rx that using sub channels, not frequency hopping, and dedicate a specific sub channel to just communicating with the Tx/Rx modules separate from telemetry and the main frequency. A Physical Link Channel, but more geared for model RC comm. It's purpose would be the selection of the best frequencies, disregarding any areas of the band (2.4 or 900 regardless) that are* too noisy, and adjusting output power relative to snr, lq and received dBm without sacrificing latency/ packet rate versus just detecting a lower received power level and cranking up the Tx, risking distortion, increased latency, potentially a damaged packet rate. Could be utilized for video in the same way.

[@sobstvenno]

@@DanJonesShow dynamic power and dynamic packet rate are different things. Crsf and ELRS have both

[@bebenoeg5188]

Thank you Joshua.👍 I always follow your lessons. May you always be healthy.. 😊

[@earry509fpv]

This has to be the best info I’ve learned this week, no lie! Thanks Josh!!!!

[@barbsfpv3066]

Great video Joshua. I just enabled this and added it next to LQ in my OSD. Thanks!

[@aphinion]

Mind = Blown. This helps so much in understanding why those receiving quality metrics never really corellated with reality. Gonna try CRSF SNR now. Thx!!!

[@sayyay6230]

You've really perfected your rock concert analogy . Great video content much appreciated.

[@kronkite061]

Bravo sir. Keep rolling out the hits!

[@DanJonesShow]

Great video. SNR is THE measurement to start with. I can have all the signal, but if my separation from the noise floor is 15dB, won't really matter

[@olafschermann1592]

You can throw SNR on a channel once you have the telemetry info back on your radio. That channel you can visualize on your OSD. A useless round trip but doable.

[@MCsCreations]

Fantastic, Joshua! Thanks a lot!!! 😃 Stay safe there with your family! 🖖😊

[@Picapiedra4]

Configured, I'll try it tomorrow, excellent video

[@traxxasru]

Jb you are as usual, top one

[@bigbellyflyer]

Thanks Joshua, from Santa Cruz Ca.

[@gmivisualsjason3729]

That was excellent and going forward I will use SNR. However on most of my builds I don't have any other osd than battery voltage. I do however have my Tx call out the Elrs power output as it changes when on dynamic. When I first did this it amazed me how much of a difference it made to match up the antennas on tx and rx. When I had horizontal to vertical the output power was up and down like a yo yo from max 250 to 10mw and I wasn't to far from myself. (Null point and kwad orientation) vertical to vertical works much better. In fact on my T-lite with max 250mw I hardly ever climb above 10mw! I'm therefore not distracted by my osd and my ears keep track of the audio alerts

[@mihavuk]

Thanks Joshua. 👍 Now we only need real life tests to prove which indication is the most reliable. You know, like years ago when you were running up and down across your property and testing various receivers. 😉😁

[@SilverbackSasquatch19xx]

Building a long range drone definitely gonna use this feature!!

[@miquelmarti6537]

I have just tried that and SNR is so much more stable easier to read. Thank you so much for the explanation. In my enviroment 4dB SNR = 27% RSSI. Do I have to change the rssi_dbm_alarm threshold or it will stay at the same point despite of unity change? Anyway it would be nice to be able to set the RSSI alarm to a given SNR value.

[@monolith2001]

I am running Crossfire and while I have not had any failsafes like I I had in my Frsky (XM+/RSXR) days, I do still get periodic "Link Quality" messages in the OSD at random times when I am not that far away. I enabled SN in Cli as you reco'd and what an eye opener as my SNR rarely gets above 25 and is often in single digits. I am running 500mW (dynamic) and wondered if maybe the power switching is causing these brief "Link Quality" messages. This happens with my Evoque, Roma V2 and Flywoo Baby 1.6 (all CRSF of course). I have a Cinerace20 coming this weekend and expect it will do the same.

[@nmrlab3807]

Any advice on where to place the antenna for the best range possible? I am using T-antenna style elrs rx on my quad and fixed wing. Thanks.

[@ismiregalichkochdasjetztso3232]

Excellent explanation, as always (and I'm saying this coming from a HAM background). But I do wonder how you managed to avoid the term "link budget" so far.

[@jamesgreenler8225]

I notice the level of interference to my GPS camera drones goes way up here in the winter when 100,000 people show up to this town all in RVs with thier own internet hot spots . This makes the range on my controls go way down and has even caused me to not have any control so I think it would be useful to see what the value is so know if I can fly in a particular area . I had a 4drc F9 go nuts and fly away and I suspect that was due to interference. Never found it . Never seen it fly that fast either 😅😁 When the seasonal people leave I have no problems with any of my drones.

[@TheMadmacs]

for me its a tough call, i fly in odd places where its possible i fly up a mountain and suddenly i see 10 people, each, no doubt, with a phone, then theres also the possibility of people approaching me where i'm sitting. i havent even sorted out lq on my nirvana crossfire/dji v2 set up yet, i think i could make the nirvana beep on the snr and then a glance at lq could tell me to expect trouble, but it would be nice to just see snr before i even take off.

[@GoneToHelenBach]

Other examples of SNR: Guitar amplifiers...turn up the gain control and noise is added to the signal between the guitar and the speaker, though this is often a desirable effect known simply as overdrive or distortion. The more you turn up the gain, the more distortion (noise) is added to the signal. Cameras...when you need to let more light in to obtain good exposure but the aperture is already at its widest and the shutter speed cannot be taken any lower without inducing motion blur, you increase the ISO, but doing so adds image noise. The ISO control applies gain to the signal (the signal is the image data as it travels from the sensor to the memory card) and the more you increase the ISO value, the more image noise will seen in the final outputted photograph. Beyond a certain ISO value (this varies from camera to camera) the image will be so corrupted by image noise that the photograph will have little discernible detail and will look like a speckled mess.

[@invertedflow]

Great explanation Joshua. One question, when turning on SNR in betaflight what happens to the dBm alarm? Does it stop working completely? Still works the same way (by using rssi dBm)? Or is it looking at the SNR value, thus the threshold should be changed? Thanks!

[@pgabrieli]

good question, I was wondering the same!

[@SilverbackSasquatch19xx]

I did this on a happymodel x12 v2.1, using the v4 Mobula 7 frame some robo 19500 motors and a Foxeer antenna with the Runcam 4 and a custom canopy I 3D printed in tpu,long story short with this turned on my link quality warning goes intermittently crazy dropping from 7:100 to 75 in very close range just flying a small circle, turned this off and everything is great again. Perhaps because the receiver is spi I need to use a different command to utilize this feature.

[@Gaby3DS]

Hi!! My Tango 2 just failsafe at 1w, 15 mts from the drone and with an SNR of 30db and a LQ of 2:100...

[@gustofpv4470]

good vid...

[@bizioFPV]

it would be super nice to have the link to the artist who made your tshirt/where to buy it in the description of every video since you basically always wear super cool FPV art tshirt, don't you think?

[@traviscornett1963]

So does this work with the custom Betaflight branch you shared in the last vid to get LQ and RSSI dBm? I tried it, but I’ve yet to even get that first part completely working. But for when I do, and others surely wondering, do the LQ/RSSI dBm hack and SNR reporting play nice?

[@raphael7003]

Joshua, how are you? I would like to know if you recommend the use of dynamic power in crossfire. thank you from Brazil

[@divingfalconfpv4602]

I've only ever looked at it after on sdlog. To see times I was close to failsafe when not too far Tons wifi towers where I am. Town city wide wifi being blasted to from optimum & others

[@AndresRodriguez-sb6ef]

From Texas

[@boostinjdm]

So what does that do to your warnings set up for rssi -dbm? Are those still active as rssi -dbm? Or has the snr value taken it's place there too? For example, my rssi -dbm warning is set at -95 dbm since I'm running 500hz ELRS. What should I do about that warning value if snr has taken it's place? Set it to something like -6 dbm?

[@JoshuaBardwell]

I believe that SNR displays in place of dBm, but the threshold still only applies to dBm.

[@oli_flies_quads]

Should the SNR on the radio have the same value as the SNR on the quad/OSD?

[@Its_ovER_FPV]

just did this command in the cli set "crsf_use_rx_snr = on" and the snr worked but the rssi also went back to 99! before it was at 80-90 when a meter between each other and then dropped of to 50-60 when between 5 rooms or so. Now it seems to be working again! using crossfire. now only drops to around 95-99 through 5 rooms when on 1w

[@tichumist6225]

Test done with rx ep1, betafpv and matek (all 2.4ghz) with 3 differents TX and RSNR (And TSNR) are between 12db and 14db. It seems that is not the same scale 🤔

[@WernerBeroux]

What about the OSD RSSI DB warning once you've set `crsf_use_rx_snr = on`? The warning level set in the CLI is based on the RSSI DB but that wouldn't capture the case of a noisy environment.

[@JoshuaBardwell]

I'm not sure whether that threshold changes or not.

[@RCRitterFPV]

Wish BetaFlight had a DJI MSP OSD button.... then the OSD tab would only show the DJI options that work...

[@KrwFpv]

Thanks alot.. Do you think frsky R9m with elrs is getting old. You dont use it anymore?

[@divingfalconfpv4602]

I use r9 lite pro with elrs915 been for a long time now. It's on my explorer. Though now that I have a JR bay transmitter I do want a new module but not sure which. But if it still works & updates & has over heating mods should be fine

[@cristianalpha7257]

I flew 6 miles yesterday; 9.5km. My tx was only putting out 25mw @100LQ. I don't think it's a major problem. At least for my area.

[@testpilotian3188]

I just go by putting the LQ on RSSI in the DJI googles and working on the principle that if it drops below 90, it’s time to turn back, because if I’m far enough away that crossfire can failsafe, I’m in a whole lot more shit for flying that far away than I am my craft failsafing and switching to GPS rescue or RTH in iNav, cos we’re not allowed to fly further than we can see in the UK. Honestly if you’re flying further than you can walk/see, you should have some sort of rescue setup and shouldn’t rely on the craft telling you you’re about to failsafe in the OSD.

[@KwadSquadFPV]

I go till it hits 70

[@km_pr]

Fun fact: emuflight offers all the link related informations in the OSD at once Sad to say, that ELRS SNR does not work for me (it says CRSF for all the link Infos).

[@gilgsn]

Best would be to aggregate the three metrics into one using an algorithm to approximate as best as possible when we approach the failsafe point...

[@kronkite061]

Wouldn’t be too hard to build the training data set for the algorithm by simulating various failsafe conditions.

[@CruxiaLz]

when using the command 'crsf_use_rx_snr = on' on the CLI, will the SNR show on the osd for ELRS recievers too or is it only for crossfire recievers quads?

[@JoshuaBardwell]

Yes it works with ELRS too.

[@CruxiaLz]

@@JoshuaBardwell oh ok, thank you for the reply!

[@yudi7974]

From Indonesia

[@LalapopApple]

I use CRSF and never have a negativ number o.O using DJI at the moment an have only one indicator for my Connection... would love to have LQ in DJI OSD

[@testpilotian3188]

There’s a fork of RC6/7 that has proper LQ on the OSD in place of the craft name, my friend uses it but tbh the one time I tried it all the numbers just confused me, I’m too used to having LQ as a channel output and setting BF to use the Aux channel that is outputting the LQ and putting that in place of RSSI and working on the principle of it it drops below 90 turn back. Has not let me down yet.

[@reuterfpv6356]

The receiver RX must always send back with at least the same transmission power as the transmitter TX, right? how does the receiver know with how much power he has to transmit? I would find that interesting to know and understand. because here in Germany you are only allowed to transmit at 2.4 GHz with 100mw. how does the telemetry receiver know that? Thanks

[@JoshuaBardwell]

The control link is one way. After a certain point the upstream telemetry will not get back from the RX to the TX but control will still be maintained.

[@reuterfpv6356]

@@JoshuaBardwell Thank you Joshua Bardwell for your quick reply. I understood that so far. but how can it be that I receive telemetry data when I fly more than 7km away. From my point of view, the RX has to send back more than 100mw or did I not understand something there correctly? all telemetry data that I receive in my TX remote control is sent back by the TX, right? kind regards Tobi

[@JoshuaBardwell]

Because the telemetry link is low bit-rate, it has greater range than the high-speed control link.

[@scottmilano2940]

Is signal to noise ratio, at least as it’s shown in betaflight really signal to noise delta? Ratio implies division, or some sort of percentage.

[@JoshuaBardwell]

dB is always a ratio. dB as a unit expresses a ratio between two things. For example, 3 dB is approximately double or half. Double or half of what? Whatever you're comparing to. Units like dBm peg the demonimator of the ratio at a fixed value to allow dB to express an absolute amount. For example, dBm is pegged at 1 mW. So 1 mW = 0 dBm. 10 dBm = 10 mW. 20 dBm = 100 mW. And so on. -10 dBm = 0.1 mW. Etc. SNR expresses the ratio between the noise level and the signal. If signal is 10x as powerful as noise, SNR is 10 dB.

[@craigdavidson52]

Do we still need to do the dbm output test at 10mw on Controller and minus 10 or does this cancel that out as I'm setting up a new quad.. Thanks for the video.

[@JoshuaBardwell]

The dBm test is still very useful for knowing if your hardware is damaged or not. kzbin.info/www/bejne/qWWolKulpaxgh9E&ab_channel=JoshuaBardwell

[@craigdavidson52]

@@JoshuaBardwell ok thanks.

[@anthonymeade4617]

It would be ideal if betaflight or flight controller could combine/calculate these measurements depending on what you select in betaflight and output a value from 0-100. Maybe also be able to preconfigure the values that it bases its 0-100 displayed connection quality. Ah pipe dreams 😂

[@saharmesri1810]

Is there an option to place a feature request on the betaflight github? Perhaps we can get some momentum by creating a feature request for 4.4 and adding comments to show support. For now it seems like the most comprehensive option is to set an alert on the radio for low RSSI dBM OR low LQ OR low SNR (with a delay so it doesn't go off when there is a slight blip). This way you get a warning even if you can't see all three on screen and can make a decision on whether or not to turn around.

[@JoshuaBardwell]

Yes you can create a new Issue and mark it as Feature Request.

[@Vousie]

@@JoshuaBardwell If you find features like this that you really think they should add, perhaps you could add a feature request on github, link to it from the video and then we could all go there and upvote it or something & then the devs would more easily be able to see whether enough people want it for them to add it.

[@snowleopardfpv]

A Betaflight GitHub PR (11062) was raised back in November 2021 to add a dedicated RSNR element to the Betaflight OSD. That PR has been earmarked for inclusion in the Betaflight 4.4 release. My comment keeps getting deleted if I include a GitHub link, so you will have to search the Betaflight GitHub repo pull requests log manually for PR 11062 if you want to see the details.

[@MrSabram07]

I have what I think is failsafe in the past and I've never sure if it's the video or the radio that failsafe how can you tell?

[@maxrackstraw]

Radio failsafe is when you can still see the video but lose control of the craft. Video doesn't failsafe but it does go bad or cant be received at all, video can go bad whilst maintaining a good rc link

[@MrSabram07]

@@maxrackstraw my guess is I get loss of video signal because it just seems like the last image I see is Frozen. So I can't control it and she crashes. So the screen didn't go blank but the image froze and I was less than a half a mile away

[@bear2180]

@Joshua Bardwell how can i get SNR on my DJI goggles?

[@timcable]

did you get an answer? Id like to know too.

[@bear2180]

@@timcable No :( based on what I've found online, DJI's OSD has very limited features and it requires improvements from DJI. but would like someone with time on his hands and know how to try to find a way around it.

[@glytch5]

Dang... I really need to fork over the doe and get onto crossfire or even tracer. I'm still using old school regular RSSI on flysky and frsky : (

[@cinemoriahFPV]

ELRS is dirt cheap and it's better.

[@glytch5]

@@cinemoriahFPV I just fired some up. Super weird to get bound but its interesting have a micro whoop that can fly around the outside of my house and not lose signal

[@IvanEfimovLimon]

Someone who knows Ghost protocol says that Ghost FW does not send SNR to BF.... maybe yet :)

[@marcino.3361]

Hey JB. Are you sure about SNR treshold? We really can't go below 0db SNR? Official lora documentation stand for: A value closer to +10dB means the received signal is less corrupted. LoRa can demodulate signals which are -7.5 dB to -20 dB below the noise floor. This is the beauty of lora modulation!!!

[@JoshuaBardwell]

LoRa can theoretically recover the signal at negative SNR. That's why you won't failsafe instantly at 0 dB. But the signal becomes very unstable and ELRS devs recommend you don't fly below 0 dB SNR.

[@woutvanwetswinkel]

In the meantime, is there any way to see both SNR and RSSI dBm on the OSD?

[@JoshuaBardwell]

Not currently in betaflight.

[@woutvanwetswinkel]

@@JoshuaBardwell Apparently, "canvas" mode is being tinkered with a lot... I saw a video by Paweł Spychalski in which he explains this, interesting...

[@tstrrtstrr745]

I don’t even display RF signal anymore in the osd. No LQ, no RSSI, nothing. With Crossfire or ExpressLRS range is more than good enough for anything. Dynamic power active, that’s it.

[@neat_fpv]

Me too , mostly because dji osd 😂 but doing long range and I don’t give a f about lq, rssi neither snr

[@deltageek7177]

One interesting complication is that LORA can actually receive signals BELOW the noise floor.

[@JoshuaBardwell]

In theory it can but the signal is kit stable enough to fly with. That's why the turn around threshold is 0 dB. You won't failsafe instantly at 0 dB but you shouldn't keep flying.

[@mjodr]

I have an SDR usb stick and learned about pulling signals from below the noise floor doing WSPR and FT8 stuff. Wild that it's even possible. Then I learned the human ear can actually do it, too. If you listen to the raw signal from an SDR tuned to a signal that's a few dB below the noise floor you can still kinda hear the signal separated from all the static. Crazy stuff.

[@Jonners]

Man it’s all so confusing. So out of all the predictable warnings that you’re about to failsafe, this is the one to do?

[@tichumist6225]

thx josh! New video: how is tememetry transmitted ? big mystery .... Is RX have... a TX ??????

[@aowi7280]

And they got rid of LQ in 4.3. Its been broke or gone for F405 boards.

[@ShinyVideoStuff]

Reason SNR isn't shown is because the values are 1) inaccurate due to clipping of the input data and 2) misleading as LoRa based signalling can work below the noise floor. SNR is in theory useful, but unfortunately pilots are going to see inaccurate and misleading SNR.

[@JoshuaBardwell]

Before making this video, I spoke to an ELRS dev who said they use SNR during testing, and who agreed that Crossfire's 4 dB to 0 dB threshold for turnaround was reasonable for ELRS. This is just two data points, and I don't have as much experience as people who have been working with this a lot longer, but at least some people with experience think SNR is useful.

[@MrSabram07]

So is Snr in DB or percentage

[@JoshuaBardwell]

dB

[@argyleskyfpv461]

Great video. Does not not work on BF 4.1.0 It does however work on BF 4.2.0

[@dash8465]

0:01 nah.. there are 4 metrics, and the 4th is the easiest and most important for most of us with Crossfire and similar, especially with dji hd.. video quality is my #1 metric for turning around. There’s only so much we can digest per second, all these various (usually) cryptic numbers become relatively useless unless its a calm high flying distance rig. But its nice to know, so I learned something today.

[@TheElectroHawk]

I understand what you're saying, but it has ofcourse nothing to do with the RC link itself.

[@Vousie]

Yeah... I'd say most FPV freestyle pilots would just use video quality and with a control link like elrs or crossfire it will almost always outlast the video. But this type of thing is much more important for long distance flyers, who might have very high gain antennas on their video link so then they might actually failsafe before video goes bad. But when JB mentioned the audio alert, I thought that'd actually be more useful for freestyle pilots - we're already not using our ears for anything and our eyes are quite busy with the video feed, so just getting a "beep" when you get into the warning range would be quite useful...

[@Ugly_Baby_Gaming]

so will this show in DJI goggles?

[@timcable]

did you find out? I'd like to know too.

[@Ugly_Baby_Gaming]

@@timcable never found out so set a shout out in my tango 2

[@DronePlayground]

👍👀🇭🇷

[@stefan_fpv]

Talking about your affirmation from 1:57: "The further away you are the weaker the signal is, the more corrupted packages there are." I don't think you're right. You could have 100 LQ but 25 RSSI and be miles out. You can see that on falconRad's video: kzbin.info/www/bejne/m2bIqHR-n9OEqrM.

[@JoshuaBardwell]

If the SNR is sufficiently high, then you'll have high LQ even at longer range. Eventually you reach a point where RSSI is weak enough that SNR gets into the range where LQ starts to drop.

[@youzrnaim]

As a person that watches a lot of KZbin, thanks for getting rid of the 10-second intro. I don’t need that. I just want the info. Thanks!

[@XtianApi]

@betaflight fix this!!!

[@BBFPV]

-8dB TSNR 🦾