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
-----------------------------------------------------------------------------------
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
From: Tim Shoppa <[email protected]>
To: Bob Stewart <[email protected]>; Discussion of precise time and frequency
measurement <[email protected]>
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 <[email protected]> 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
-----------------------------------------------------------------------------------
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
