[time-nuts] Disciplining a Rubidium with a Thunderbolt.
wb6bnq at cox.net
Tue Jul 12 08:44:11 UTC 2011
Just to clear the AIR, all Rubidium frequency standards have a crystal oscillator as
the primary signal source within the Rubidium device. The Rubidium portion of the
standard is just a very high Q filter whose properties can be controlled such that
it's filter's center frequency has extremely small drift. That small drift factor is,
typically, way less then the resulting factors that control drift in a Quartz
In order to gain the properties of the Rubidium's longer term stability and the short
term noise properties of a very good Quartz oscillator you would need both items. You
select a very good Quartz device and phase lock it to a really good Rubidium (with its
own Quartz oscillator). You would adjust the loop constants to correct at a very slow
pace consistent with the quality of the very good Quartz oscillator.
To get to the next level (connection to the Nation's reference), you would discipline
the Rubidium against a GPS device with an even slower loop. So, in the end you have
two separate loops with three separate devices. This is not your "Nickel & Dime
store" plug-and-play set up. It would have to be set up with care and some
experimentation to get it right.
For a reference on the basic process, you should read the QST article on Brooke
Shera's GPS disciplined oscillator system. Contained within it is a description of
the loop process I referred to above. To utilize his method would require upgrading
his circuit design (some parts not available any longer) and some software upgrading
as well to account for those changes.
To obtain the QST article go to Shera's web site at http://www.rt66.com/~shera/
Also click on the "more information line" for further reading.
"Dr. David Kirkby" wrote:
> On 07/12/11 02:15 AM, Tim Tuck wrote:
> > Hi all,
> > Just wondering how many people have used John Miles work @
> > http://www.ke5fx.com/tbolt.htm, or similar, to discipline a rubidium
> > oscillator and if so...
> > 1. what was the RB of choice ?
> > 2.have any measurements of phase noise etc. been published on such a rig ?
> > 3. Are there any published how-to's etc. available ?
> > I'd like to build such a beast as my lab standard so any help appreciated.
> > thanks
> > Tim
> I'm no expert on this, but I believe that the rubidiums have poorer phase noise
> than crystals, so unless holdover performance is an issue, there is no advantage
> in using a rubidium over a crystal as long as GPS lock is maintained at all times.
> The Stanford PRS-10 rubidium looks to be quite nice, as it has a 10 MHz crystal
> to give good phase noise and also the rubidium for medium term stability. It can
> be disciplined easily, as it has a 1 pps input.
> Alas the PRS-10 is not as plentiful (i.e. cheap) as some other rubidiums.
> There may be better ways, but a PRS-10 and a timing receiver which outputs 1 pps
> looks to be a relatively easy way to get the short term peformance of a crystal,
> the medium term performance of a rubidium should the GPS get unlocked and the
> long term stability of GPS.
> I'm looking for a lab standard too, so I'd be interested in what other replies
> you get. For me personally, for a short term solution, I'm thinking of using an
> undisciplined rubidium.
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