Does RSSI has a max value?

Does RSSI have a max value? I have noticed
that some RSSI’s values are positive numbers. Sometimes when I send data vary closed to the gateway, the RSSI’s value is +5 or other positive numbers.

But most of the time, the RSSI should be a negative number when I far from this gateway.
Is +5 an expected value?

In addition, The RSSI is always a negative value when the data frame send by my another gateway from another manufacturer(RAK). Although the sensor device is very close to the RAK gateway, the RSSI is -19 or other negative numbers.

I think that the RAK gateway is to be expected. Does RSSI have a max value? Does 0 is RSSI’s max value, even if it never be reached?

If you see an RSSI of higher than -40 or so, there’s a fair chance your node is too close to the gateway and overloading the receiver; this can cause data errors, false signals on additional channels, etc.

Another cause of very high RSSI numbers could be conversion/math errors in software misinterpreting a reading, especially any custom, unique software you may be using.

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Is it probably that the gateway’s manufacturer calculate the RSSI using wrong algorithm?

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Most / all gateway vendors are using the Semtech HAL, I don’t think vendors are doing their own RSSI calculation, but I might be wrong. Note that there is a rssi_offset configuration option in the packet-forwarder config. This affects the reported RSSI.

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