[time-nuts] Next upgrade

Adrian Godwin artgodwin at gmail.com
Wed Nov 22 23:08:40 UTC 2017


I've got several of the Ref 0 boxes but none of the Ref 1. I've added an
Oncore GPS receiver to one of them as per Peter Garde's notes and it works
well.

But I'd like it to run with an unmodified Ref 0 too in the ref0/ref1
configuration. Not that I need an HA reference but just for interest. I've
only had a quick look so far and found that connecting the two together
with a 15-pin cable didn't work.

Has anyone looked into this ?


On Wed, Nov 22, 2017 at 11:01 PM, Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
>
>
> > On Nov 22, 2017, at 5:16 PM, Jerry Hancock <jerry at hanler.com> wrote:
> >
> > Three questions:
> >
> > 1) Now that I’ve split my Lucent RFTG-U into a REF0 and REF1 unit with
> both supplying 10Mhz and 1PPS, is there a way to combine the outputs or
> some other technique to improve the short and/or long term performance?
>
> You can monitor one against the other. Ideally you would want three
> GPSDO’s and a
> monitoring setup. That way you can figure out which of the three has gone
> bad.
>
> >
> > 2) I’ve become interested in Rubidium Disciplined Oscillators recently
> and was now thinking of purchasing one of the PRS-10 that I see on Ebay. If
> I did that and replaced one of the DOCXOs from one of the Lucent boxes,
> what impact would this have on the overall performance both with and
> without (when in hold-over)?
>
> If you go into holdover, you are the exception. Most setups rarely go into
> holdover. When they
> do, it’s because a hurricane just went over the house. Generally that’s
> not when the focus is going
> to be on timing experiments.
>
> > Basically, is it worth the money to upgrade one of the boxes to a
> Rubidium disciplined oscillator assuming the GPS signal is rarely lost?
>
> Not worth the money if you are only looking at holdover and have a typical
> setup.
>
> >
> > 3) Figuring the PRS-10 will cost around $250 when all is said and done,
> is there a better option to improve my GPSDO system?
>
>
> Disciplining implies continuously correcting. Rb standards age much less
> than a typical
> OCXO. Oddly enough their temperature stability may not be as good as a
> high end
> DOCXO. It is fairly common to try to stabilize the environment your
> standards operate in.
> To the extent you are successful this reduces the need to deal with
> temperature.
>
> The net effect is that disciplining an Rb at a rate (filter / control loop
> / manual tweak) of less than
> a few days actually makes the Rb worse. Coming up with software to “back
> off” on the tuning is
> not as simple as it might seem.
>
> This comes back to the fact that the GPS signal (or any of the sat
> signals) are quite noisy. You
> need to average them over a *long* time to get good performance. Rb’s are
> enough better than
> a GPSDO OCXO that the time ranges really stretch out ….
>
> >
> > I basically use the GPSDO as a reference for any equipment that takes an
> input. I have no monetary need for a reference, just an interest.
>
> For most normal test equipment, a GPSDO output is “plenty good enough”. As
> a source for fancy
> timing experiments … maybe not so much. As a phase noise reference or a
> spur free source for
> microwave games … also not the best way to go.
>
> Bob
>
>
> >
> > Thanks.
> >
> > Jerry
> >
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