This is a completely different problem, is it? Bandwidth is orthogonal

to the concept of dynamic range and amplitude values.

Anyway, your FFT plot knows about complex samples; therefore, it

displays dB relative to the numeric value of “1.0”; this has nothing to

do with your input signal power. But since USRP/daughterboards tend to

work linearly over most of their available power range, you can just add

a multiply_const to your signal processing flowgraph and get your value.

The factor, however, depends on your ADC/daughterboard combination, on

the gain you set for the RF frontend, a little bit on temperature, the

tuner, the impedance matching of your RF input to the Daughterboard etc.

So if you already know what you’re putting in, just use this as a

reference and “calibrate” yourself.

Hope that helped clear things up,

Marcus