[Elecraft] Rb & GPS DO comparison

[Brian Alsop]

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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