[Discuss-gnuradio] Re: wrong dB

[feldmaus]

Martin Braun <braun <at> int.uni-karlsruhe.de> writes:
> 
> Here, you're comparing with something else. There's a lot of stuff
> between the coax connector and your software, so you can't trivially
> translate sample values into Volts. Calibrating a USRP/GNU Radio setup
> to actually measure physical units is not easy. That's why it uses 'dB'
> and not 'dBW' or 'dBm', it's merely a relation.
> 
You are right. There is many stuff between USRP and my Generator, but
the difference between -11.933dB(W or m) to -60dB is very big.
So there should be a misunderstanding or big problem ?

Therefore i tested the output of my hardwaregenerator
with a hardware scope. My cables are ok.

Which dB is shown on the FFT-Plot ?

I also tried it on my own python program with the following
modules:
[USRP Source]-->[Compl_To_Mag]-->[Throttle]-->[FFT-Sink]

Is that ok to analyze the magnitude and freq of my sin signal ?

Or do i have to pay attention to decimation, sample rate and
IF Frequency to not violate the Nyquist criteria ?

Regards Markus