[time-nuts] Thunderbolt accuracy...??

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Dec 20 22:08:41 UTC 2008


Hej Magnus

Magnus Danielson wrote:
> Bruce Griffiths skrev:
>   
>> Mike
>>
>> A statement of accuracy is of little value unless you also give:
>>
>> 1) An estimate of the accuracy of standard used for comparison.
>>
>> 2) An estimate of the random and systematic errors in the comparison
>>
>> 3) Some details of the comparison method.
>>
>> 4) Averaging time and other pertinent info.
>>     
>
> True, but for an hobby enthusiast we could be a little less stringent 
> (as long as we remember we are cheating) if the goal is to say: Be able 
> to measure and maintain my 10 GHz signals to within 1 Hz on long term.
>
>   
Some description of the method and resolution at least is desirable.
If the some parameters arent known at least say so.
If the method isnt well defined no one else can make comparable
measurements on their frequency reference.
> Achieving the frequency stability below 1E-10 for tau = 100s and above 
> should not be too hard to achieve and some fairly easy means of 
> monitoring the state of a Thunderbolt should be able to indicate wither 
> this is met or not.
>
>   
You are being vague, do you mean ADEV, MDEV or what?
High frequency stability is only part of the  requirement, the relative
frequency offset also has to be known.
> It's not that we can't achieve better performance, but if we do not need 
> to be near the cutting edge but rather have fairly relaxed requirements, 
> let's not complicate maters more than necessary. The one thing we do 
> want to say is that things needs to be monitored, since there may be 
> many sources which could make the functionality be severely degraded or 
> lost.
>
>   
No excuse for omitting measurement technique details.
Such info is essential if others are to make meaningful comparisons with
their own measurements.
> Many forget the performance supervision aspect. GPS receivers in 
> particular seems to be (fairly) cheap magical boxes which makes things 
> work, and then they are forgotten all about until something breaks. The 
> type of actions needed to handle the case when the service is degraded 
> depends. For a ham it may very well be that he just does not really know 
> where he is on the spectrum right now... but the years of previous 
> measurements could at least given him some confidence on how much he 
> could expect to be off now that he is not able verify or steer his rig.
>
>   
The important requirements appear to be that the clocks at the 2
stations should agree to within a small fraction of a second and that
the relative ADEV of the receiver and transmitter LO frequencies for tau
of a few seconds needs to be better than around 1E-11 (for the upper end
of the SHF band). To make effective use of microsecond time offsets
between station clocks would require fully automated operation and
taking the propagation delay of the transmission path into account.
> (Sorry for the stereotypic identification of a ham as being "he", I know 
> for a fact there is female hams out there and also sharing the same 
> concerns as any male ham on where she is on the spectrum, but it was 
> just convenient to type it like that.)
>
> Cheers,
> Magnus
>
>   

Bruce



More information about the time-nuts mailing list