[time-nuts] Spectrum Analyzer Specifications

jimlux jimlux at earthlink.net
Wed Mar 23 10:04:14 EDT 2016


On 3/23/16 4:11 AM, Bob Camp wrote:
> Hi
>
> If you can see harmonics down to -60 dbc, that is about the most a normal spectrum
> analyzer will do for you on a frequency standard. This *assumes* the part has a sine
> wave output. Most standards are in the 10 MHz range, so an analyzer that will work to
>> = 40 MHz is probably a good idea.
>
> Can you do this with a USB gizmo? Sure you can. Can you trust the results? That will
> depend on the exact unit you get and your ability to calibrate it. Might it “only” be useful
> to -50 dbc? Might it work to -100 dbc? That is part of the “did you pay $X or 10 times
> that much question.
>


Spectrum analyzers are also nice when debugging a new circuit.. 
unexpected oscillations at other frequencies, spurs, etc.

For this kind of thing, limited dynamic range isn't as big a problem. 
Would the difference between a 8 bit and more bits in the ADC make a 
difference? Maybe, maybe not.

However, with respect to this new analyzer, the thing to really look at 
is the software that runs it.  Does it do what you need it to do, 
*today*?  Does it work on your PC platform (Win, Mac, *nix), *today*?

Today is important.  There may be all sorts of planned upgrades (and 
hey, lots of folks do "open source", so conceivably, someone else could 
do the upgrade), but they may never materialize: the people doing the 
work may get onto another project; there's not enough market for what 
you want.

More than one software controlled device I've worked with worked fine 
with the supplied software, but what I was really interested in was 
controlling it with other software, and the promised open API never 
really existed, was documented, or delivered.

This is particularly pervasive in the amateur radio community, where the 
original developer was motivated to "scratch an itch", solved their 
problem, and then cast their product out to the big wide world, along 
with grand plans to make it even better, then found that it was more 
work, and work that didn't scratch the itch.

Likewise with products/software that are the result of somone's masters 
or PhD thesis.  They get far enough along to finish the dissertation, 
publish it as open source (good for them and us), but there it 
languishes, 85% complete, with all the (useful to me) corner cases 
untested or undeveloped.


In neither of these last two, would I cast aspersions on the authors (or 
even forge and machine aspersions<grin>): they did what they said they 
were going to do, and in general, their description of what they 
actually did matches what they did.



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