[hpsdr] Blocking dynamic range of SDR

[Marco IK1ODO]

At 21.55 22/04/2008, Chris Stratton wrote:
>..
> >For an SDR receiver, the blocking dynamic range is
>the >distance between
> >the ADC full scale (clipping) level and the noise
>floor.
>
>I'm not sure I agree with that, as it seems to assume
>that the ADC is perfectly linear, which we know it
>isn't.
>
>I believe you would need to measure the noise floor in
>a filtered bandwidth at some spacing from a high input
>signal that is simultaneously present to get a true
>measure of blocking dynamic range.
>
>If you measure the max signal before clipping, and the
>noise floor separately, then what you've measured is
>the ordinary dynamic range, not the blocking dynamic range.

Hello Chris,

in principle I agree with you, and, yes, I tried. Only, there is 
practically no variation in noise floor, until the ADC saturates.
I used a clean XTAL (HP 10811A) as signal, followed by an attenuator. 
The low level signal is unaffected, or, at least, you don't see the 
classical 3dB (S+N)/N impairment.
So, since the ADC fs treshold is quite a limit, I decided to use it. 
Simply there is no "soft" blocking as you see on an analogic 
receiver, and the phase noise is so good that there is no sideband 
noise compromising the dynamic range.


73 - Marco IK1ODO / AI4YF 


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