[time-nuts] 35601A as stand-in for 11848A ?

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Jan 6 22:59:51 EST 2008

SAIDJACK at aol.com wrote:
> In a message dated 1/6/2008 15:01:25 Pacific Standard Time, jmiles at pop.net  
> writes:
>> 85671A package or mine, how _exactly_ are you turning the dBc/Hz  values you
>> get from (say) the 8561E into your ~-120 dBc/Hz  numbers?  Let's hear the
>> step-by-step procedure on that, and the  problem should reveal itself.
> Hi John,
> by selecting a 1Hz RBW on the 8561E. The APII analyzer should have a 1Hz  BW 
> normalization as well, although I checked in the user manual again and it  
> just specifies "dbm" without regards to RBW. How does one calculate RBW from an  
> FFT? Is it the width of a given FFT bin? I will check this again, and try to  
> increase the number of samples.
> But even with say a 10Hz RBW I would expect the noisefloor to only rise  
> 10xlog(1/BW) or 10dB, much less error than what I am seeing.
> bye,
> Said

1 Hz resolution bandwidth isnt the same as 1Hz noise bandwidth.
The noise bandwidth of of a 1Hz resolution bandwidth depends on the
details of the filter.
For an FFT analyser, selection of  a Hann, Blackman-Harris, uniform or
other window function/filter changes the equivalent noise bandwidth of
the filter.


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