[time-nuts] ADEV vs MDEV

Bob Camp lists at cq.nu
Sun Feb 7 00:26:21 UTC 2010


I believe the statement:

"Both systems are equally limited by the reference oscillator"  

was part of the same paragraph as the comment on 10811 short term stability.

Neither system, no matter how well set up will get below the stability of the reference oscillator. 

I have indeed read a lot of threads here. I've also tested a *lot* of oscillators. Finding a 10811 that consistently does <=1.0x10-^13 at 1 second is *not* an easy task.

Far more to the point - the tight loop requires a voltage controlled reference. Weather it's a 10811 or something else, it needs voltage control. The heterodyne approach does not. You do  need to get luck with your frequencies if the heterodyne reference is not tunable. Something like a 10811 is indeed needed in a tight lock system. 


On Feb 6, 2010, at 6:55 PM, WarrenS wrote:

>> "An ADEV noise floor of 1E-13 isn't likely when using an HP10811A as the VCXO for example."
> How quickly one forgets and gets lost on these long topics.
>>> "If you accept that the measurement is going to limited by the  Reference Osc,
>>> for Low COST and SIMPLE,  Can't beat a simple analog version of  NIST's "Tight Phase-Lock Loop" "
> And which method are you saying is NOT limited by the Reference Osc??
> Correct, not going to get to 1e-13 at one sec with a HP10811A,
> nor likely with any other Ref Osc that most Freq nuts have.
> SO Seems like that is GOOD enough noise floor limit to use for a "low cost & simple" configuration.
> A well setup "Tight Phase-Lock Loop" method will go below that..
> and a good HP 10811A can go below 1e-12 at 0.1 sec. (at a bandwidth of 30 Hz)
> ws
> ***************
> Bruce Griffiths said:
>> The noise of the OCXO used as a VCXO will limit the noise floor.
>> An ADEV noise floor of 1E-13 isnt likely when using an HP10811A as the
>> VCXO for example.
> Bruce
> *****  Original Topic *************
>>> I would appreciate any comments or observations on this topic.
>>> My motivation is to discover the simplest scheme for making
>>> stability measurements at this performance level; this is NOT
>>> even close to the state-of-the-art, but can still be useful.
>>> Pete Rawson
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