RSSI never higher than -52

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1

After getting back into Meshtastic and updating to 2.2.24.e6a2c06, I have started doing some range surveys with the current setup and I noticed what I think are unusually low RSSI. On my latest test, I haven’t gotten over -52 indicated RSSI on a TLORA V2 with the best SNR being 12.5, even when the devices are pretty much next to each other.

Devices:
TBEAM M8N, rubber ducky
TLORA V2, external GSM antenna

Measured the antennas with a NanoVNA and they are OK for 868. Tested also with different antennas.

Edit: I get the values from the LORA V2 via MQTT

2 
> select device,rssi,snr from telemetry where time > now() - 24h
name: telemetry
time                device   rssi snr
----                ------   ---- ---
1711535975268651415 f244e3c4 -81  12.25
1711537687799518867 f244e3c4 -65  12.25
1711540943964439100 f244e3c4 -99  11.75
1711544545772513038 f244e3c4 -75  12.75
1711559007519521038 f244e3c4 -98  11
1711565102820159893 f244e3c4 -62  9.25
1711565600763665304 f244e3c4 -61  10.25
1711570613229916189 f244e3c4 -58  13.5
1711573594586239863 f244e3c4 -59  13
1711574495050709581 f244e3c4 -59  13.5
1711575395503108834 f244e3c4 -59  13.75
1711606437529609275 f244e3c4 -52  11.75
> select device,rssi,snr from position  where time > now() - 24h
name: position
time                device   rssi snr
----                ------   ---- ---
1711541223841030588 f244e3c4 -105 6.25
1711541284012284961 f244e3c4 -105 8.25
1711541344689653310 f244e3c4 -113 5.75
1711541404851548403 f244e3c4 -114 3.5
1711541464458332484 f244e3c4 -112 3
1711541525189434250 f244e3c4 -111 6.25
1711541584751009435 f244e3c4 -105 9
1711541644893333778 f244e3c4 -112 4
1711541825833534194 f244e3c4 -127 -12
1711541885472715632 f244e3c4 -121 -4.5
1711542005796949128 f244e3c4 -127 -6.5
1711542065987757049 f244e3c4 -134 -12.5
1711543389458913668 f244e3c4 -134 -13
1711543450132089620 f244e3c4 -130 -8.75
1711543510371686924 f244e3c4 -134 -15.75
1711543570482787750 f244e3c4 -121 -2
1711543630700422875 f244e3c4 -129 -6.75
1711543871166288325 f244e3c4 -129 -7.5
1711543930828636935 f244e3c4 -112 7.5
1711543990914395743 f244e3c4 -109 6.5
1711544051068356860 f244e3c4 -106 6.75
1711544111705293383 f244e3c4 -86  12
1711544171453736817 f244e3c4 -74  13.25
1711544231516173978 f244e3c4 -71  11.5
1711544632111496978 f244e3c4 -54  12.25
1711544696496624603 f244e3c4 -52  12.25
1711544753675854443 f244e3c4 -102 10.5
1711544813640058400 f244e3c4 -122 -2.75
1711547342982330807 f244e3c4 -116 3
1711547403170091773 f244e3c4 -94  12.25
1711547463914813018 f244e3c4 -76  11.25
1711547523405576667 f244e3c4 -77  11
1711547584081281986 f244e3c4 -55  12.25
1711547644337279340 f244e3c4 -52  13.5
1711559144322154242 f244e3c4 -95  10.5
1711559207642320717 f244e3c4 -93  10.25
1711559268330611295 f244e3c4 -98  10.25
1711559328511934041 f244e3c4 -104 7.5
1711559388131138466 f244e3c4 -112 4
1711559448224091477 f244e3c4 -105 8.25
1711559508344329747 f244e3c4 -106 6.5
1711559629160248337 f244e3c4 -112 1.25
1711559689230206792 f244e3c4 -119 -1
1711559749500112550 f244e3c4 -130 -10.25
1711559869345072792 f244e3c4 -129 -8.75
1711559989561970279 f244e3c4 -127 -12.75
1711560110349196804 f244e3c4 -125 -7
1711560170039948490 f244e3c4 -111 0.75
1711560230151212457 f244e3c4 -110 6.5
1711560351070056380 f244e3c4 -72  10.5
3

RSSI of -52 dBm and SNR of 12.5 dB are pretty high values for LoRa.

4

Is it any better in the evenings? If so, do you have solar on your house?

In Australia, I have 5kw solar panels on roof, with a Growatt 5000MTL grid-tied (240v) inverter, and it blasts the 900Mhz area of spectrum with a lot of noise. At night, when my house solar turns off, my RSSI improves significantly. Between two RAK4631’s, I get -29 RSSI when a few meters apart. When the sun comes out and the solar comes on, that RSSI increases to -45.

5

@GUVWAF
With the devices basically right next to each other, I’d expect positive dBM…

@ROX1
No solar. I actually checked 869.525 (I’m in the EU) with an RTLSDR and my noise floor seems to be around -49dB.

-52dBm would be 0.0000063096 mW. That’s quite little for 2 radios putting out 27dBm (500mW - at least according to configuration) 5cm apart from each other. Even if the radios would put out 100mW (20dBm), -52 would be shockingly little.

6

I’ve never seen positive dBm with LoRa. However, the RSSI measurements are an approximation made by the radio and it’s not accurate for high values, see the relevant part of the datasheet below. Note that they mention >-100dBm is already high!

image
image864×358 25 KB

that’s quite little for 2 radios putting out 27dBm (500mW - at least according to configuration)

The configuration is just the maximum of the region, but it will be limited by what the radio can do. T-LoRa v2 uses SX127x series, which can do maximum 20dBm (assuming the accompanying hardware is perfectly tuned). It depends on which T-Beam version you have, but it might also be a SX127x. The SX126x series can do 22dBm.

7

@GUVWAF
So it’s the usual RF black magic :D.
OK then, thanks :slight_smile: