[time-nuts] Any thoughts on best rubidium?

Jose Camara camaraq1 at quantacorp.com
Fri Sep 23 17:04:36 UTC 2011

I think you are right, often the internal, free running osc will give you better results. You can use the GPS or rubidium to calibrate the internal one just before you need some more accurate absolute frequency measurements on the SA. 

It will depend on what measurement you are making, and whether phase noise or frequency accuracy is more important. For day to day use, the external ref will work, except when perhaps you need to look at very close skirts, where maybe the internal alone can give you lower noise. In most cases, you don't really need either (checking a filter, EMI, radio output, etc.) but a lot of thing in this list is because we can, not because we need.  :-)

Get a real clean, low phase noise 3rd signal, measure it using the internal and external osc, look at the skirts. They might even be the same, if the limit is elsewhere in the SA signal chain.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Robert Deliën
Sent: Friday, September 23, 2011 9:25 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Any thoughts on best rubidium?

I'm missing the PRS10 in this list. I have been wanting to buy one for a long time, but didn't because it has been a solution to no problem for all this time.

But now I have bought a spectrum analyzer, a Rohde & Schwarz FSIQ3, with tracking generator and lots of options. It would be nice to have a PRS10 as it's external reference. I already bought a Resolution-T timing GPS receiver to discipline it over the long term.

But PRS10 standards are quite rare lately: I think I've seen only on eBay in the past year and prices have doubled since the time they showed up in numbers. And I'm starting to doubt if it will be worth the effort. My instrument has the B4 option, for low phase noise. The specifications of the internal reference are pretty good:
Aging per day					1x10−9
Aging per year					2x10−7
Temperature drift (0°C to +50°C)	8x10−8
Total error (per year)				2.5 x 10−7
No phase noise specifications on the internal reference are specified, but a plot for the instrument overall is (http://www.livingston-products.com/products/pdf/130413_1_en.pdf).

I'm starting to wonder if connecting PRS10 as an external reference would actually improve overall accuracy, because it may introduce extra phase noise. And even if I've finally got one: How to tell it's an improvement without a reference?

Any thoughts please?

>> * FE-5680A
>> * SLCR-101
>> * Efratom 10MHZ Rubidium FREQUENCY Standard FRS-C
>> Is there any reason to chose one over another for the application I have?

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