[time-nuts] Re: HP 8663A: option 003

[Bob Camp]

Hi

The other (possibly obvious) thing with the 3048 is that you have taken
out the carrier by the quadrature downconversion process. That happens
before you ever get to the spectrum analyzer(s). 

Indeed the HP analyzers from “back in the day” had pretty limited bit depth.
That was as good as it got for the era. 

Even without the 3048 hardware, you can breadboard up a quadrature setup
for < $100. Run it into a good sound card and you will have phase noise
data. There will be ground loops to deal with. There’s also some math to get
the calibration right. The ground loop part also comes in if you run the 3048.

Software wise, there are a number of free “spectrum analyzer” programs out 
there to get your sound card data captured and (in some cases) normalized
to 1 Hz bandwidth. 

Bob 

> On Apr 23, 2023, at 9:28 PM, John Miles via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>> Which brings me to the question of the interfaces (I have none of
>> them, but do have two 8662s and would be interested in making some PN
>> measurements). The 3047 used the spectrum analyser interface 35601A
>> which I know almost nothing about and the 3048 used the 11848A for
>> baseband or 11729B/C for mixed down measurements. Are they all equally
>> useful today, possibly with a more modern FFT analyser as some of
>> those HP dynamic signal analysers have very low numbers of bits in the
>> ADC even compared to a soundcard!
> 
> Given that a 3048A system isn't too expensive to put together, it's probably
> not worthwhile to assemble a 3047A system today unless you already have a
> 35601A and 3582A ready to go.
> 
> Unfortunately the various FFT analyzers made by HP are completely
> incompatible with each other due to different GPIB command sets.  Only the
> 3582A can be used with the 3047A software, and only the 3561A can be used
> with the 3048A.
> 
> Bit depth is not a concern for two reasons, one being that the interface
> boxes have a number of variable gain stages to make the most of the
> available dynamic range, and the other being that you're going to be
> measuring at 1 Hz resolution anyway, so the effective bit depth is higher
> than what the hardware ADC provides.
> 
> -- john
> 
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