[time-nuts] The home time-lab

Bob Stewart bob at evoria.net
Fri Jul 8 14:53:40 EDT 2016

Hi Tim,
I've learned a lot from the responses to my original post.  I had almost come to the conclusion that a UPS wasn't going to do it for me before I started this.  Unfortunately, I can't afford to have a Generac running 24/7, so I was hoping for alternatives.  The idea of an inverter type system sounds good in theory.  The cost and complications were a concern.  It's probably more of a case of "fear of the unknown" than anything else.  But, I was uncomfortable with actually going out on a limb and putting one together.  So, I ordered a 1KVA Sola constant voltage transformer.  With any luck, it'll do enough that my testing will settle down.  If not, then I'm going to add a power-line monitor of the type using a small transformer and a sound card.  That would identify times where tests weren't reliable.  And that should be enough.

Thanks to everyone who posted.  I certainly got my money's worth!


      From: Tim Shoppa <tshoppa at gmail.com>
 To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
 Sent: Friday, July 8, 2016 1:27 PM
 Subject: Re: [time-nuts] The home time-lab
Everyone else is talking as if these blips can be protected from, by having a UPS supplying your precious lab equipment.
I strongly disagree.
What happens, is you have transformers, fluorescent ballasts, and motors (e.g. HVAC blowers) in the vicinity of your lab equipment. Probably on a completely different AC branch circuit, and not even necessarily in the same room but maybe in an adjacent room or above or below your lab. With an inductive load, every time there's a sudden power cut, a large back-EMF develops and then the power suddenly comes back on and then there's a sudden large current as the magnetic fields are built back up. It's these transient magnetic fields from your non-lab equipment, that is what's disrupting your measurement.
If you now add a UPS in the vicinity of your lab equipment, and it of course has a transformer in it, it will likely add to the disruption in a power glitch.
Of course things are a little different if you banish all AC power from a few hundred feet of your lab and only run sustaining charging current for the DC batteries developed in a far-away DC supply :-).
Tim N3QE
On Thu, Jul 7, 2016 at 8:44 PM, Bob Stewart <bob at evoria.net> wrote:

I hope this isn't too far off topic, as this is having a big impact on my testing.

I decided to run an A/B test on one of my GPSDOs: comparing the phase of the two 10MHz output channels.  In the middle of the night, there was a long series of 35ns pops in the phase data.  Strangely enough, there was nothing in the data collected directly from the unit involved.  The preceding two days we had had a number of switching transients where the lights blinked but nothing shut down.  So, putting one and one together, I suspect that a fair percentage of the strange results I've been getting has been power-grid related.
So, what to do?  I've been looking at UPS devices, and I don't even understand enough to waste my money on a bad one.  The two big questions seem to be "on-line" and "sine wave".  Make that three: can I trust the mfgs claims?  Is there something affordable that could run a pair of 5370s and maybe another 50W worth of DUTs for up to an hour or two and not be prey to power-line transients?  Or would it be more cost effective to somehow monitor the power line for spikes or phase jumps and blow off tests or cut out the offending data?  From time to time we get a thread on power-line nuts.  Should I have been paying more attention?

Bob - AE6RV
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