RSSI calculating

Hello .
I am working on my ground station. sure i am using MAVLINK. i can show 3dr telemetry rssi( like mission planner’s notification bar) on my software.
and i do this like that :

LBT RSSI calculation :

to do this :
i am sending HEARTBEAT message to pixhawk at every 1 second and pixhawk send me RSSI_STATUS message.

after i get rssi value , i use this formule :

signal_dBm = (RSSI / 1.9) - 127
(i guess this formule was using for 3dr Telemetry)

my question : i have a new data link system. it’s signal power is 33 dbm ( sensitivity -100dbm@4Mhz ) and 2 watt.
now how can i calculate signal_dbm value according to my new data link device ?

edit : my data link device doesnt have rssi output channel port.

thank you …

It depends on the chipset that your radio is using. In the datasheet there must be a table to relate rssi register value to dBm, plus you have to know the firmware, because the register value could be altered before passed along. So in a nutshell, it is entirely depends on the manufacturer.

thank you for reply.
But i cant understand. rssi value is a integer ( 0 - 255) that pixhawk is calculating according to heartbeat message timing, isnt it ?
another problem. i dont know a firmware or RSSI register about data link device.
just know, it is 33 dbm ( sensitivity -100dbm@4Mhz ).

Nope, rssi value in the RADIO_STATUS packets is coming from the rssi register of the radio transciever chip. These packets are inserted into the mavlink datastream by the radio.

But at this reply, no need to transciever chip register. Because pixhawk looks at time of between sending and getting mavlink hearbeat message . am i wrong ?

Unfortunately yes you are wrong. On the link above they telling, that if the 3dr radio sees mavlink heartbeat packets then it injects the RADIO_STATUS messages into the datastream.

But if you step back and think for a minute, how can the rssi relate to the airtime of a fix length packet ? Lower rssi does not mean that the propagation speed of the radio waves are changed :smiley:

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ooh that was very useful information for me :blush: i can see now. in this state , i am in trouble .
do you have another advice for me to show signal strength of telemetry.
i have not firmware or rssi mavlink ouput in data link device.

If you can give the type of the data link device, perhaps I can figure out something. But there is a possibility that there is no way to tell the RSSI.
The only thing that can be done is to count missing packets, and if it starts to rise then you know that you are at the limit. However it can be misleading if your radio implement some sort of ECC.

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this my data link device:

i need to show signal strength on own ground station. i hope we can find a solution.

Isn’t it have some sort of web interface ? (It seems it is nothing more than a glorified wifi router with some serial to ethernet converters) If the signal strength is displayed on the web interface then you can poll it with a simple program on the ground station.

I find the user manual. No luck, and it will not start dropping packets until it is too late. :frowning:

yes it is showing rssi on web interface . but i cant get this value.

Get wireshark or similar network sniffer, connect via the setup program capture the communication and try to reverse engineer the protocol, if it shown on the interface then you can get it via a direct connection.

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you are right . i will try :+1:
or second way, how can i calculate signal strength with mavlink packets on serial port ?