[time-nuts] time-nuts Digest, Vol 21, Issue 22

Robert Lutwak Lutwak at Alum.mit.edu
Fri Apr 21 05:34:08 EDT 2006

The extra 3 kHz or so is due to the buffer gas shift of the Rb hyperfine 


Robert Lutwak, Senior Scientist
Symmetricom - Technology Realization Center
34 Tozer Rd.
Beverly, MA 01915
(978) 232-1461   Voice           RLutwak at Symmetricom.com   (Business)
(978) 927-4099   FAX             Lutwak at Alum.MIT.edu  (Personal)
(339) 927-7896   Mobile

----- Original Message ----- 
From: "Normand Martel" <martelno at yahoo.com>
To: <time-nuts at febo.com>
Sent: Thursday, April 20, 2006 10:44 PM
Subject: Re: [time-nuts] time-nuts Digest, Vol 21, Issue 22

> Help me! I need explanation!
> Robert Lutwak wrote:
>>With that said, the Perkin-Elmer rubidium on the IIR
>>satellites is an outstanding clock, unquestionably
> the
>>best rubidium ever manufactured for any application,
>>with short-term stability an order-of-magnitude
> better
>>than the IIF cesiums.  The drift is also remarkably
>>low for a rubidium oscillator, compared to commercial
>>rubidium, and, with daily updates, they will
>>outperform the cesiums, though the cesiums will beat
>>them outside of a week or so.
> Well, i've got the PDF brochure for the Perkin-Elmer,
> and it's indiscutably an outstandingly superb Rubidium
> frequency standard (458 000 hours MTBF!!!), but
> there's something that ticks me here, and i've seen it
> on other rubidium standards. Let me explain:
> On the brochure, the output frequency is 13.40134393
> MHz and in the RF section of the block schematic, we
> can see that the 13.40134393 MHz OCXO is multiplied
> 510  times (classic x6 followed by an SRD x85) before
> driving the physics. If my calculator is OK, that
> gives me 6834685404.3 Hz. However, the hyperfine
> transition of Rubidium is at 6834682612.8 Hz! A
> difference of 2791.5 Hz (0.40843 PPM)!!!! I don't
> understand! That's not a Lada, that's a "Ferrari"
> grade standard!
> As i wrote earlier, i've seen a similar difference on
> another (Efratom, if i remember) Rb standard! Can
> someone explain me? I don't understand!
> Thanks for your attention!
> Normand Martel
> Montreal, Canada
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