Nano- gateway rssi

[bmarkus]

Are you talking about ERP? No antenna gain in the formula.

[jcaron]

The basic principle is that you reverse a link budget equation to find the free space path loss component, and then find the distance for that component.

RSSI = TX Power + TX gain - TX loss - Path loss + RX gain - RX loss

So

Path loss = TX Power + TX Gain - TX loss + RX gain - RX loss - RSSI

If you change antenna, the same TX Power and path loss give a different RSSI (and vice versa). This affects the computation (the value of n in the OP's formula).

[MJ]

@jcaron
I am using the RSSI in order to get the distance. But which formula should i refer to? Because this is a backup for my project which in the jungle their will be no signal so using the rssi value i can get the distance.

[bmarkus]

@mj said in Nano- gateway rssi:

@jcaron
I am using the RSSI in order to get the distance. But which formula should i refer to? Because this is a backup for my project which in the jungle their will be no signal so using the rssi value i can get the distance.

You can't use RSSI to calculate distance on a reliable way. Environment has an ifluence, like rain, vegetation plus if device is moving changing antenna position.

[MJ]

@bmarkus
Using rssi to calculate the distance is just a test. So is it still can make it to get the distance?

[bmarkus]

@mj said in Nano- gateway rssi:

@bmarkus
Using rssi to calculate the distance is just a test. So is it still can make it to get the distance?

Sure, the only question is the accuracy and what do you want to achive :)

[MJ]

@seb
As u mentioned the TX power will remained the same unless we change it. But how can we change the TX power in the module?

[seb]

@mj
https://docs.pycom.io/chapter/firmwareapi/pycom/network/lora.html#class-networkloraid0-

Please see the tx_power parameter of the lora constructor.

[MJ]

@seb
Is there any chances to obtain the RX power?

[seb]

@mj

The RSSI value from lora.stats() is "the received signal strength in dBm" as per: https://docs.pycom.io/chapter/firmwareapi/pycom/network/lora.html#lorastats

[MJ]

@seb
But from lora.stat() it does not have the RX power. how can i obtain? Is there a way to obtain?

[seb]

@mj

What do you mean by RX power? The RSSI is the power of the signal that was received measured in dBm.

[Burgeh]

@seb When I have two LoPys close together, and connect through raw LoRa my RSSI is still around -30dBm that seems bad for such a close range. Putting them even further away (10m) puts them around -60dbM. Is this about right?

[seb]

@burgeh

Yes -60dBm is a reasonable value for LoRa

[robert-hh]

@burgeh Looking at the discussion in this link: https://electronics.stackexchange.com/questions/83354/calculate-distance-from-rssi
and the derivation of the inital formula furtehr down the side, it seems that TxPower in the formula cites by MJ is the RSSI seen at a distance of 1 m. In my tests with two LoPy, that was in the range of 25dBm. Assuming that the power decrease by the suqre of the distance, 60dBm for a 10m distance seems not complete off, maybe a littel bit higher than expected (40dBm difference -> factor 100 == 10**2).

[MJ]

@robert-hh I have tested again by pointing the antenna straight upward in 1m the rssi value that i obtained is around -37dBm. Is it looks reasonable?

[robert-hh]

@mj Depends on the antenna an it's set-up. With a short wavelength/4 antenna, I had values between 25 and 39 dBm, even depending on how I was placing myself. The wavlength/4 antennas are typicall about 10cm (4") long, whereas wavelength/2 antennas have a length of about 20 cm (8").