Understanding RSSI dBm limits / is my range poor / TX setup incorrect?

[fading basin]

Hi all. Can someone help me understand RSSI dBm limits, and what to - and not to - be concerned about?

Since my post here the other day #1233517605235462164 message I've gotten a good result in bench test (-25 RSSI dBm), but flying even 100m away LOS I see my RSSI dBm value drop to -70/-80 pretty fast. Which I didn't expect.

Thing is, I don't know what TO expect! Can anyone put my mind at ease? Is that normal?

I tested with a second quad (Cinelog35 with CRSF RX [and bigger T antenna], vs my Pavo25 with ELRS) and saw similar results/values, so I've been scared to fly much further away in case of failsafe.

Could there be an issue with my transmitter AND/OR ELRS module? (Tango2 Pro with Happymodel 2.4GHz ELRS module). Is one/both antennas not able to give me decent range? (I can't believe that's the case but I don't know for sure, so I'm asking).

Might I need to change a setting on my transmitter? I was reading https://www.expresslrs.org/info/signal-health/#rssi-sensitivity-limit and I think I'm on 500Hz. Is this good/bad or indifferent? Should I change it so that the sensitivity of RSSI dBm is lower and I don't need to worry so much about losing signal?

Reason I'm worrying about all this, perhaps too much, is I have my first paid FPV gig coming up very soon... the flying part / skill required doesn't worry me (after 2+ yrs of flying FPV at this stage, and longer with non-FPV commercial work), but I don't want to lose signal unexpectedly at 'short range' while flying in and out of buildings.

Thanks for any reassurances / tips!

[misty bear]

500Hz on a Tango 2 is not really advised

the Tango 2 can only do 250Hz at best, due to hardware limitations (primarily how its gimbals are wired up and its sensor itself(

each of the packet rates have accompanying dBm values which is their sensitivity limits, which is the rssi dBm value you would expect to get a link loss

lower packet rate tends to have a much higher sensitivity limit

then, there's also a concern regarding power (voltage and current) delivery

the tango 2, given its 1S battery pack, won't be enough to sustain the expressLRS module at higher power level.
so I would suggest keeping the transmission power level on your tx module to 250mW max.. anything higher and you're risking brown-outs on the module/radio

trust can't be gained overnight

[fading basin]

I'm 100mW max (CE) anyway, so I'm on 100mW.

Is that an issue?

[misty bear]

comparing 900MHz against 2.4GHz on their rssi dBm values is kinda like comparing apples to banana. They have different noise levels, depending on the prominent noise frequency
e.g. a 900Mhz link will do well compared to 2.4GHz in an urban environment with lots of 2.4GHz wifi..

[fading basin]

OK. I did see slightly different RSSI dBm numbers initially (before arming), so that makes sense 🙂 I'm mostly worried about the drop in that value with both protocols though -- like I said, to -70/-80 within 100-150m LOS. Is that normal/expected?

Either way, I should change the setup on the Tango2 to 250Hz rather than leaving it on 500Hz, yes? (which I've never changed, to my knowledge).

Also, thank you for quick responses, super appreciate it 🙂

[misty bear]

yes, use 250Hz on the tango 2.. anything higher will only cause issues on your rc trace..
setting it to 500Hz will mean you're asking for 250Hz more when it can only supply 250hz.. causing your RC trace to show up as stair-stepping..

rssi/rssi dbm is logarithmic..
so the values do not change linearly, vs distance/range

[fading basin]

OK, so it's a rapid change at first, then the change should decrease at longer range? (hope I got that the right way round!)

[misty bear]

yes.. and near the end of the link budget, it will fall off quickly again..

so it's imperative you'd be vigilant near that edge (e.g. 5 to 10 db from the link sensitivity limits)

[fading basin]

Sure. OK thanks!

[fading basin]

Just gonna leave this here for anyone else in future, JB's video about RSSI dBm values and footage that shows (at around 5 mins in) values in the -90s as he's flying around his house, so I'm much less worried about seeing values of -80 in my OSD now!

https://www.youtube.com/watch?v=LnWdIssBk-c

Also worth noting BetaFlight's default (at the time of writing) for its osd_rssi_dbm_warning value is -60, so I've changed that to a more reasonable number to avoid being totally freaked out in future 😄 (while also leaving Link Quality and RSSI dBm Value enabled in the OSD at all times).