[time-nuts] ADEV vs MDEV
warrensjmail-one at yahoo.com
Sun Feb 7 01:14:28 UTC 2010
> 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
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.
----- 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
> 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
> 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.
> 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
>> 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.
>> ***** 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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