[time-nuts] Small Symmetricom GPSDO

John Green wpxs472 at gmail.com
Sun Feb 21 12:55:59 EST 2016


I have been playing with one of those small, 2.75"by 4.5" GPSDOs that are
being sold on that auction site. Most of the ones I have seen any
discussion about have been Trimble, but this Symmetricom one looks similar
but is about half price. I have hooked it up a few times to see how fast it
can find satellites and how the LEDs work. Yesterday, I hooked it up and
compared the 10 MHz output to my Z3801 which has been running for about a
month now. I am using my Racal 1992 counter in time difference mode. It has
a resolution of 1 ns. The 10 MHz isn't present until it has "locked"on
satellites. Or at least I presume that is it. I didn't get any 10 MHz for
about the first 10 minutes. At first, it looked pretty stable. Then, I
decided it wasn't.  Now, I'm not sure. It acts differently to the Tbolt I
tested in the same manner before. While the Tbolt would sit steady on some
arbitrary time difference for maybe a half hour and then move 30
nanoseconds or so in a minute only to settle down again for a while, this
thing just slowly drifts back and forth. After thinking about it, I think
that is how it was meant to operate. It seems to have been an internal
piece of some other, larger piece of equipment. In that role it was most
likely meant to provide either 1 PPS, 10 MHz, or both at pretty good
accuracy pretty quickly after getting power. It isn't as good as say a
Z3801, but then I don't think it was meant to be either. It certainly isn't
nearly as big. I may put it in a case with a power supply and a buffer amp
and use it for an everyday standard. I certainly think it is good enough
for that. It seems happy running on 6.3 volts at around 600 ma. after warm
up. Has anyone else had any experience with one of these? What did you
think of it?


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