[time-nuts] Re: Phase Station 53100A Questions

[John Miles]

> I think you may be heading a bit off track digging into the 5120. The
> 53100a has a very different “heritage” than the TSC gear. The 5330
> “TimePod” would be a better thing to dig into to see its history. I’m
> guessing 52100A is a typo.
> 
> The .TIM files are generated by TimeLab so that’s a good place to look
> for grubby details of this or that. They are “just” text files with a lot of
> embeded comments that document what’s what on each line.  Maybe
> not *quite* a “just read it and it all makes sense”, but there is a lot of
> information in the file itself. I would suggest starting by reading through
> the file that TimeLab puts out.

What Bob says. :)   It's true that the .TIM file format is meant to be self-descriptive to some extent, but it's also true that we really ought to document it formally at some point.  I've been holding off for the next major revision of the file format, which is intended to support multichannel measurements and per-sample metadata in a single file.  That will probably be an extensive-enough overhaul to render existing documentation obsolete.  That said, feel free to email me -- or post here -- if you have questions.

> 2.  There will be some debugging required in my test setup, and it
> would be very useful if I could independently demodulate the
> Amplitude Modulation (AM) and Phase Modulation (PM) components of the
> phase noise, and present the low-passed waveforms in voltage versus
> time form.  Signals leaking in for other places may well be
> recognizable by resemblance of the demodulated AM or PM baseband
> waveform to other signals known to exist in the system under test.  I
> was thinking that the TIM file may be a start.

This would really need to be addressed with direct access to the I/Q data stream from the hardware, which isn't on the road map right now.  If the goal is to track down signal leakage, though, it is very effective to look at the AM and/or PM spurs, and also the frequency-difference view.  As long as you select a measurement bandwidth that's wide enough to include the source(s) of concern, they will show up as periodic artifacts in frequency difference measurements as well as ripple in the ADEV trace.

As far as the fundamental principles of operation go, they are covered reasonably well in the manual.  Again, any specific questions, just say the word.  The TSC patents are mostly aimed at working around deficiencies in the early RF ADC chips and DDS IP cores that were available when Sam Stein's team did the original groundwork.  I wouldn't say they're a waste of time to study, but they are of historical rather than operational interest.  As a source for further reading, the 5120A/5125A manuals are likely to be more helpful than the patents.

-- john (TimeLab support guy)