[time-nuts] Beginner's Atomic Clock

[Dana Whitlow]

All of the available Rb standards that I've seen have a 10 MHz output,
Some have a
1 PPS output as well.

The nice thing about a Rb is that its short term stability (seconds to
minutes and perhaps
even longer) is much better than that of a GPS timing receiver.  The bad
news is that Rb
standards exhibit long term frequency drift in the neighborhood of a few
parts in 10^11
per month.  A pretty fair compromise is to use an Rb standard that is
disciplined by GPS
PPS pulses with a loop time constant on the order of a day or so.  The SRS
model PRS-10
seems to be well-regarded and can be had for $1500 factory new.  Many are
on sale by
ebay and similar sources- however these are often left over from telecom
service and
are actually a modified model that has had the PPS locking facility removed
so that the
original buyer could save a few bucks.  My PRS-10 is one of these.

The Rb standards seem to prefer being powered up continuously, and if one
is turned back
on after any significant storage without power, it can cake several days to
really settle down
to its steady state behavior.  Also, because of the long-term frequency
drift, one must
periodically retune the unit back on frequency by referring it to GPS.
Both units I own
(a PRS-10 and an L-PRO) have an analog tuner port, wherein application of 0
to 5V DC
tunes the frequency of the Rb through the range of +/- a few parts in
10^9.  This has been
straightforward but a bit tedious; if I want to get it within a few parts
in 10^12, even a good
10-turn pot is barely adequate to the task, and I'm sometimes turning the
shaft through
an angle so small that I'm not sure I even moved it until I've observed the
phase drift
against  GPS for an hour or more.

So, that's my version of Rb 101.  See what others have to say as well, as
I'm also fairly
new at the game.

Dana   (K8YUM)


On Mon, Sep 16, 2019 at 4:02 PM pisymbol . <pisymbol at gmail.com> wrote:

> First off, thanks to everyone who replied.
>
> On Mon, Sep 16, 2019 at 11:00 AM Bob kb8tq <kb8tq at n1k.org> wrote:
>
> > What are you really trying to do here?
> >
>
> Take over the world - one epoch at a time.
>
> If it’s a “from scratch” atomic standard, then you just aren’t going to get
> > there. Sorry about that ...
> >
>
> Ok.
>
>
> > If it’s a wall clock sync’d to an external radio service then indeed you
> > might get there.
> >
>
> Well, I want something maybe in between. Currently I think I have that: I
> have a RPi disciplined to the Adafruit Ultimate GPS HAT via chrony (PPS
> etc.). This works well.
>
>
> > In-between those two lie tings like buying eBay telecom Rubidium’s,
> > attaching them to a power supply and you have a working standard.
> >
>
> So I think this is what I'm talking about. I want something a little bit
> more esoteric than a GPS 1PPS. Can you explain a bit about these
> prepackaged Rubidium standards? Upside/downside etc. Do I have to
> maintain/check these black boxes?
>
>
> > Lots of very different directions this could go and and they all could be
> > called an atomic clock …. Not at all knock on doing something, just
> > confusion
> > about what exactly you want to do.
> >
>
> Again, take over the world. Sorry for not being upfront about that. That
> would have made things A LOT clearer.
>
> So I guess: How can I get a simple Rubidium standard that outputs a
> reference frequency as a discipline to say ntpd or chrony.
>
> Btw, I'm a noob. Please be gentle.
>
> -aps
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>