On 04/25/2014 10:30 PM, Tom Van Baak wrote:
Hi Everyone,
I'm newer to this forum but I really enjoy reading the discussions. I have
a pretty basic question.
I'm wondering why one would chose an Rb Oscillator over a traditional OCXO?
It does not immediately appear there is a phase noise advantage in the Rb..
Thanks,
~Shane
Welcome to time-nuts. Good question.
In some applications the exceptional long-term frequency accuracy and stability
you get with Rb is more important than the better phase noise, smaller size,
lower power, better short-term stability, longer lifetime, or cheaper price
that you get with an OCXO.
When you buy a new OCXO, it might be accurate to 4 or 5 or 6 digits,
out-of-the-box. You have to mechanically (screw) or electronically (EFC)
calibrate it to get closer. If you want, say, 9 digits of accuracy, then you
may have to re-calibrate it every day or at least once a week.
When you buy a new Rb, it might be accurate to 9 or 10 or 11 digits,
out-of-the-box. If you want, say, 9 digits of accuracy, then you may have to
calibrate it every couple of years.
Size, weight and cost may also be issues.
In todays age of modernization, a well-sized OCXO or rubidium isn't an
option, and well, smaller OCXOs exist while rubidiums starts to become
really scarse below a certain volume, and when the volume come downs
further, the CSAC is the only atomic reference and then you only see
OCXO and TCXOs.
Cost-wise some high-performance OCXOs gives the rubidiums a match
performance-wise (even if they need a bit more trimming) but not
price-wise or even volume-wise.
Them some telecom rubidiums just isn't very good at phase-noise, but
have fair stability for the size and cost.
In the end, there is no one choice which always fits, it *really*
depends on what you need it for, and the requirements, then it plays
itself out as you look through the options.
Cheers,
Magnus
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