[time-nuts] Running voltages through MVAR (In re: HP5065)

Tom Van Baak tvb at LeapSecond.com
Sun Aug 23 15:13:23 EDT 2015


I abuse ADEV too! It really works well in some cases, doesn't it. Very clever of you to try it on a 5065A with voltage, current. etc. I assume you use the y-form (frequency) not the x-form (phase) in this case?


1) The scale is more intuitive, I find, when sqrt is used -- so I'm curious why you chose MVAR instead of MDEV?

2) When plots mostly head down with a -1 slope, consider TDEV instead of MDEV, which effectively rotates by 45 degrees turning -1 slopes into 0 slopes. For some kinds of data a rise above a normal (zero) slope is more informative than a bend of a steep -1 line. Psychologically too, it removes the "things are working better and better as time goes on" impression that happens with a -1 slope, e.g., when ADEV is used on data from a locked loop.

3) Before you settle on MDEV, also try ADEV. There are cases where the massive averaging inside of MDEV ruins interesting noise periodics that would show up in ADEV. Then if you want to combine (2) and (3) you can compute ADEV(tau) * tau. Look at http://leapsecond.com/tools/adev5.c for the undocumented z flag. Like the real TDEV is to MDEV, this is a sort of TDEV for ADEV, but without the sqrt(3). It plots a zero slope where ADEV would plot a -1 slope.


----- Original Message ----- 
From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Sunday, August 23, 2015 11:16 AM
Subject: [time-nuts] Running voltages through MVAR (In re: HP5065)

>I have decided it is finally time to come clean about one of my
> "trade secrets":  I sometimes run voltages through MVAR.
> Sometimes I also run temperatures, kilowatts and anything else
> I happen to have a time-series of through the MVAR.
> In this case, it tells us a lot about why the C-field current of
> my HP5065 is unstable:
> http://phk.freebsd.dk/hacks/HP5065A/20150822_mvar/index.html
> I'm not done collecting data for the resulting effect on the HP5065
> performance, but so far it looks like the MVAR floor is half of
> what it used to be.
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
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