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LoRa or wifi ..... max received signal strength -20bBm?

davebullockmbe

Can someone explain why no matter how close I place my two Lora evaluation modules next to one another (or my phone to my wifi hub) I never achieve a signal strength higher than -20dBm?

Is there some form of AGC in the receivers that prevents the input from exceeding -20dBm input, or do the TX/RX combinations communicate with each other to throttle back the TX power?
I have been bemused by this when fiddling with wifi in the past,  but now I find that Lora is exhibiting the same behaviour despite the specified TX power being much greater and the antennas almost touching one another.. 
Clearly I am missing something? 
Can someone point me to the idiot's guide as to why this is occurring please?

Thanks
Dave

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  • in reply to anniel747

    Hi thanks for your replies.

    Yes but WHY -20dBm ?
    What scientific principle limits receivers to only report -20dBm no matter how strong the field strength?
    I just tested my mobile phone running 'wifi analyser' app. near my wifi hub and from about 40cm to right against the hub the signal never wavered from -25dBm. A normal CW signal would have varied logarithmically as expected according to the laws of physics (ignoring multipath!)
    What anomaly of physics are these devices employing to "defy the laws of physics Jim"?
    Joking aside, I know -20dBm is recognised as a strong signal, but why -20dBm and not 0dBm or +20dBm.
    I have mostly measured RF power referenced to zero dBm so what's going on?
    Dave