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Re: [Discuss-gnuradio] rssi questions

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] rssi questions
Date: Tue, 07 Aug 2007 14:22:44 -0700
User-agent: Thunderbird (X11/20070604)

Brian Padalino wrote:

> Is this really the RSSI - or should the RSSI actually be a function of
> the amount of gain or attenuation in the RF stages?  I am sure it gets
> pretty difficult calculating an estimate for the amount of power at
> the antenna.

It's a "digital RSSI" value, meaning it's based on the output of the ADC
and not the true RF power at the antenna.  Furthermore, it's really a
single pole low pass averaging filter on the absolute value of the ADC
value, with no way to adjust the time constant.

You would have to use this value on the host, which has knowledge of the
daughterboard in use, gain settings, ADC configuration, etc., to
estimate the Rx power.

> Should this value be an expression in dB of the received power?

That would be nice, but would require actually measuring this in the RF
front end using some sort of logarithmic amplifier or square law
detector.  This has it's own disadvantages as it diverts power from the
receive chain (and of course adds cost, power, complexity, and board space.)

Johnathan Corgan
Corgan Enterprises LLC

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