[GPS_Standard] Interesting QEX article, GPS help needed!

[Bert, VE2ZAZ]

Hi Bob,

Yes, I have read the article. The author does mention that the Rb oscillator
can be disciplined using GPS-derived systems (such as mine). While this is
true, I don't see the real benefit of doing this. Here is why.

Rb oscillators have a good long term accuracy, so they drift much less over
a long period (months, years). They perform much better than OCXOs in
free-running applications. But this comes at a price: around $300 on the
used market. So their prime target application is a standalone,
non-disciplined reference. In GPS-disciplined applications, the Rb
oscillator's inherent long term stability is lost since you adjust the
oscillator every hour or so. Why would you pay this much when you can get
the same long term performance for 1/4 to 1/3 the price with an OCXO?

Rb oscillators have other drawbacks. Their short term stability and phase
noise characteristics are worse than good OCXOs (such as the HP units). The
Rb lamp has a limited operational life, usually guaranteed to be at least 10
years when purchased new. Do you know how much life is left out of that unit
you see on Ebay? Also, Rb oscillators are fancier devices and adjusting them
is not as trivial as tweaking a potentiometer (I have not tried it myself
but this my understanding, so don't quote me on this). There are a few
adjustments and doing a good job requires knowledge of the inner guts, field
adjustments, etc....

There is a good summary of the relative performance of different oscillator
types at the following IEEE link:

http://www.ieee-uffc.org/freqcontrol/quartz/vig/vigcomp.htm

I hope I have answered your questions.

73's

Bert, VE2ZAZ


----- Original Message -----
From: <k7hbg at dslextreme.com>
To: <gps_standard at mailman.qth.net>
Sent: Friday, November 30, 2007 10:10 PM
Subject: [GPS_Standard] Interesting QEX article, GPS help needed!


Hi Bert
 After reading the article by John Raydo, "Atomic Frequency Standard" in
the latest QEX issue I knew that I must possess the Rubidium Standard
featured in the construction project.
 Have you seen this article? If you have, I'm sure you noted the reference
to your star performer. Could you give us any thoughts on using your GPS
unit with the Rubidium unit to further enhance its accuracy and
stability?
 Best regards, Bob K7HBG







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