[time-nuts] Any thoughts on best rubidium?
magnus at rubidium.dyndns.org
Mon Jul 11 00:06:21 UTC 2011
On 07/11/2011 01:37 AM, Dr. David Kirkby wrote:
> I'm looking to get a rubidium source to use as a reference for a
> spectrum analyser, frequency counter or similar test equipment. All
> these need a 10 MHz input.
> I've looked on eBay and found a few that seem to be in plentiful supply
> * EFRATOM 10MHZ LPRO-101
> * 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?
For the spectrum analyzer, if dynamics and closed-in noise is dear to
you, the closed-in phase-noise becomes of interest to you. The wide
phase-noise will mostly be canceled by the bandwidth of the lock-in PLL
and replaced by the spectrum analyzers own noise.
For frequency counters it really depends. Some will just switch in
whatever you feed them and others will phase-lock to it. If you
phase-lock, then high-frequency noise on the input is mostly cancelled
by the PLL bandwidth, but for those that switch in, the full bandwidth
becomes visible. Granted, it needs to be fairly noisy to make a huge
impact on measurements. Mid-term stability (1-1000 s) is however where
most of the rubidiums should give you quite a good match regardless.
It might be worth-while to use a good low-noise oscillator locked to a
rubidium to get the mid-term stability from the rubidium and short-term
from the oscillator. Granted, there will be a noise-bump as the
cross-fade between these phase-noises occurs.
I can't recall exactly which specs the above rubidiums have. However,
some of them are more modern and have a MCU sitting there and keep some
control-loops which the others doesn't have, and added stability is to
Anyway, now you should see how I reason with preferences and such.
Hopefully you can put it together with your equipments behaviour and
your measurement needs and then spec sheets to a suitable solution.
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