[time-nuts] LF power supply noise

Magnus Danielson magnus at rubidium.dyndns.org
Sun Jun 21 16:01:33 UTC 2009


>   Hi Magnus,
>   I was having the same problem with funny colors until I  switched to
>   LCD monitors. The problem went away:)
>   I did  try putting a large steel plate between the  543310A  and the
>   2467B. The plate was 12"X12"X1/4" (30.48cm X 30.48cm X 0.635cm), and
>   I checked  it  with a magnet to verify it was magnetic,  but  it had
>   little effect.

Maybe it was not a suitable variant of steel. I used a pair of backsides 
from a pair of 10 U Schroff racks, no particular steel at all, and it 
proved useful to reduce the effects. Just as Bruce pointed out, steel is 
not one thing, but magnetic permeability can change quite drastically, 
so I just had good luck where as you didn't have such a good luck. Also, 
aligning it properly for the field should increase the coupling effect 
between the steel and the transformer... which is the important part.

>   One of  the  reasons  I was attracted to the  543310A  was  it could
>   display 14  digits  of frequency in one second.  Sine  then,  I have
>   figured a  way to resolve 16 digits in one second, so  that  part of
>   the spec is no longer interesting.

As was described by J. J. Snyder in "An Ultra-High Resolution Frequency 
Meter" in the FCS 1981 (as available from IEEE UFFC) I assume, basically 
using the fact that adding more measurements in a dense time raises the 
degrees of freedom and allows for quicker interpolation.

Modern counters like HP 53131, HP 53132 as well as Pendulum CNT-90 or 
Fluke 6690 uses similar approaches.

As being reported, such mechanisms does not fair well with ADEV 
calculations, and especially the overlapping variants of ADEV and den 
MDEV and TDEV which was inspired by that particular article, so using it 
twice forms unwanted filters.

>   The 543310A can do a single-shot time measurement with  a resolution
>   of 200ps, and gets down to 1ps with averaging. The HP5370B does 20ps
>   single-shot, and  will  resolve  100fs with  averaging.  But  I have
>   figured a  way  to measure 2ps single-shot, and  a  bit  better with
>   averaging. So that part of the spec is not so interesting any more.

I assume you really mean HP 53310A and not HP 543310A, even if your 
typing is consistent. The listed numbers is when weigthing in how 
various jitter sources combine upon averaging and should be considered a 
bit conservative.

By all means describe what you mean by 2 ps single-shot resolution.

>   The 543310A  will display the phase and frequency changes  in  a PLL
>   step response.  But  you  can get  the  frequency  response  just by
>   looking at the VCO DC error voltage. And if you look at  the voltage
>   across the  bottom  capacitor in a type 3 loop,  you  get  the phase
>   response. Here's a picture:
>   -------------------------> to VCO
>         |
>        --- C1
>        ---
>         |
>         |----------O < -  Phase Error
>         |       |
>        --- C2   \
>        ---      / R1
>         |       \
>         |       |
>        ---     ---
>         -       -

You should recall that when HP built their line of analyzers, they where 
thinking "what can we make this cool ZDT core do?" rather than 
attempting to build the best analyzer for all responsens.

>   So about  the  only  thing left of  interest  is  histograms  of the
>   jitter. Unfortunately,  the 543310A cannot store  enough  samples to
>   really make an interesting graph. What I would like to be able to do
>   is similar  to an invention I made for the disk  industry  long ago,
>   called Phase Margin Analysis. There is a brief description on my web
>   page at
>   http://pstca.com/patents.htm#phasemargin

Somewhere in my map of apps there is a HP appnote for doing the same, to 
discs, intended for disc industry, back in the days.

The HP 5372A and onwards (HP 5373A and HP 53310A) include hardware 
histograms, to increase the rate of histogram builing. Use that rather 
than the software more histograms. I don't know the details for the HP 
53310A as I have never used one, but having a look at them it looks like 
it also has the fast histogram measurement engine, which is also 
described in detail by the patent... the HP 5371A did not have the 
hardware histogram, so it uses software instead.

>   There is  a  more  detailed description  in  the  paper,  "Effect of
>   Bitshift Distribution on Error Rate in Magnetic Recording",  by Eric
>   Katz and Tom Campbell, at
>   http://pstca.com/pdfs/katz.pdf
>   But it doesn't look like the 543310A will be able to do that.
>   Now that I can beat most of the performance specs of the 543310A, it
>   doesn't seem  worthwhile  to  spend much time  trying  to  solve the
>   problem of stray magnetic fields.

The 53310A was a nice convenient tool at its time, but it's performance 
isn't up to spec with modern times. It seems like HP didn't pursue it 
into much deeper levels after its VXI instruments, where as others went 


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