[Elecraft] Rb & GPS DO comparison

[Igor Kosvin]

"Anybody got a hydrogen 
maser handy?"
I do. Not at home of course, but at work. We actually manufacture them. If
you really want to test your GPS DO, let me know. This is the company that
made LPRO as well. Here are some numbers for you:
LPRO accuracy spec when it left the dock - better than 1e-11 (relative
frequency. Multiply by 10,000,000 to get frequency offset in Hz), aging
drift - better than 1e-11 per month. Useful life of LPRO - usually 15 years.
Make your math how much it drifts over life.
GPS satellites have either very good Rb clock or average Cs clock. The
accuracy spec of recovered GPS clock is better than 1e-12. The drift is not
important because the clocks up there are adjusted once in a while to keep
accurate.
Hg maser is mostly praised for frequency stability, not accuracy per se, but
its accuracy is also impressive - better than 1e-14 after 1000 seconds
averaging.
By the way, if you have way to use GPS Do with your K3, I would prefer that
over LPRO. You did capture pros of LPRO. Here are the cons: high power
consumption (need to heat large Rb lamp and resonant cell to over 100C°) and
limited life. The surplus one you get from eBay is probably have most of it
useful life gone.
73,
Igor, N1YX  

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Brian Alsop
Sent: Wednesday, July 20, 2011 2:41 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] Rb & GPS DO comparison

Guys,

This may be of some use to those interested in locking the K3 to an 
external source.  The issue of what kind of source to used has been the 
subject of a number of postings.

Clifton labs did the above comparison. Jack's Rb standard came in at 
about .0004 Hz relative to a GPS DO at 10MHz.

I was wondering how accurate the EBAY purchased LPRO-101 Rubidium 
oscillator was.  (I wanted to use it as a master oscillator for my test 
equipment and perhaps later the K3.)

Comparisons to WWV indicated that in all liklihood it was well within 1 
Hz.  There was no way to determine if it drifted within that range.

Curiosity finally got the best of me.  I purchased an EBAY Trimble 
Thunderbolt GSP Disciplined oscillator.  Supposedly, it is more accurate 
than the Rb secondary standard. Assuming it's truth, the Rb secondary 
standard was evaluated via the phase drift method using a dual channel 
scope.

Out of the box, the Rb standard came in at 0.0075 Hz (10 MHz) of the 
GPS-D0. With a little tweaking of the ten turn pot in the LPRO-101, the 
two are well within 0.001 Hz (nominally 0.0008Hz) at 10MHz.  There is a 
small drift component of 0.0002Hz after 3 hours after lock. Tweaking 
isn't straight forward.  The appears to be a few minute latency period 
after a tweak.  One can't simply stop the phase angle from moving by 
turning the pot.  Doing so results in an over correction a few minutes 
later.

It's difficult to tweak the Rb standard beyond this degree of accuracy. 
  It takes more than 20 minutes to determine a data point.  To do better 
would take some automation and a phase detector running for several days 
to get sufficient statistics.  Next project is building a phase 
detector.....

I'm pleased.  The Rb standard has lots of advantages:  Price, minutes to 
locking on, portability and simplicity.

The next question: How accurate is the GPS-DO?   Anybody got a hydrogen 
maser handy?

Now what to do with the GPS-DO?

Remember when decent receiver dials had only 5 KHz markings?

73 de Brian/K3KO






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