[Elecraft] Rb & GPS DO comparison

[Ken Alexander]

Hi Brian,

Interesting post.  I've read of others using GPS this way, but what does this kind of accuracy buy you when maybe 1 in 100,000 other hams go to this kind of trouble?

73,

Ken Alexander
VE3HLS


--- On Wed, 7/20/11, Brian Alsop <alsopb at nc.rr.com> wrote:

> From: Brian Alsop <alsopb at nc.rr.com>
> Subject: [Elecraft] Rb & GPS DO comparison
> To: elecraft at mailman.qth.net
> Date: Wednesday, July 20, 2011, 2:41 PM
> 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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