[time-nuts] ADEV vs MDEV

[WarrenS]

Bruce said
> tight PLL method is useless for comparing GPSDOs or rubidium  standards 
> for long Tau

wow, Again we agree, but are off topic again.
Tight PLL is not the answer to everything (Just the hard things, like small 
Tau).
If you are suggesting a DMTD as a cheap and simple solution for long term 
ADEV numbers and drift,
You've  lost the whole point of how this all started, low cost and simple 
"1e13 at 1 sec".

There are so many simple, cheap and easy ways to do LONG term drift and taus 
to 1 part in 1e13, and Yes they all start with Phase.
Use phase for long term and use Freq for short term,  IF you like simple.


ws

*******************

----- Original Message ----- 
From: "Bruce Griffiths" <bruce.griffiths at xtra.co.nz>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Saturday, February 06, 2010 4:09 PM
Subject: Re: [time-nuts] ADEV vs MDEV


> As long as one limits oneself to measuring 10811As or similar for short 
> Tau.
> However the tight PLL method is useless for comparing GPSDOs or rubidium 
> standards for long Tau unless one replaces the VCXO with a sufficiently 
> very low ADEV.
>
> The DMTD system doesnt have this limitation as the reference source isnt 
> phase locked.
> The reference can be a GPSDO or an atomic standard without requiring any 
> modifications.
>
> Until you have actually demonstrated that results obtained using the tight 
> PLL method agree with the results obtained with accepted methods then one 
> has to remain suspicious of the range of validity of the technique.
>
> Bruce
>
> 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.
>>
>> BTW
>> 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
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to 
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
>
>
>
>