[time-nuts] The home time-lab

Bob Stewart bob at evoria.net
Thu Jul 7 21:49:25 EDT 2016

Hi Tim,
I don't see how it could be related to a clock chain in my unit.  I'm quite literally running the two outputs from one unit through about a meter of coax each to the 5370.  These two outputs are from a single 74HCT365.  Pins 12 and 14 of the chip (the inputs) are tied together, and pins 11 and 13 each go through a 50 ohm resistor and a 0.1uF cap to an SMA connector.  So, even if the software did something really bad, I don't see how it could cause such a blip in the data.  This should be measuring just the hardware, not the software.  The other input to the 5370 is the PPS pulse from the LEA-6T on the unit buffered through a M74VHC1GT125, which I use to gate the time sample through the EXT input.  The EXT level is at preset.  And since I had had a few anomalies days before, I set the A and B channel levels to about midpoint in the active range.  I'm using 50 ohms, divide by 10, DC, positive slope on both inputs.  I had gotten the same sort of thing days before using preset on all inputs.

By the way, I've seen exactly the same sort of thing on my other 5370.  It was one of the reasons I chose to get the "new" one.  So, unless it's something inherent to the 5370, it pretty much has to be something external to the test setup.  The only thing I can think of is the power grid.

Bob -----------------------------------------------------------------------------------

      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: Thursday, July 7, 2016 8:16 PM
 Subject: Re: [time-nuts] The home time-lab
1/35ns is about 30MHz. Is there anything in your clock chains that is ticking at 30MHz, such that a false count or slipped count induced by inductive disruption, would cause a 35ns phase jump?
Related thread: https://www.febo.com/pipermail/time-nuts/2016-May/098028.html

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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