[time-nuts] Small Symmetricom GPSDO

Bob Camp kb8tq at n1k.org
Sun Feb 21 13:06:59 EST 2016


Hi

Both of these little beasts likely have much of the same basic smarts as their 
older / bigger cousins. The OCXO may or may not be quite as super low
phase noise as some of the others. Based on that, I would expect them to 
need to run for several days at least before you see what they really do or
do not do. That’s certainly the case with the Z38xx’s. It also applies to the TBolt, but 
in a somewhat different way. 

Bob

> On Feb 21, 2016, at 12:55 PM, John Green <wpxs472 at gmail.com> wrote:
> 
> 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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