[time-nuts] Frequency Ensemble

[Bob kb8tq]

Hi

TAPPR needs that order for 25 TICC’s …… :)

There are indeed many ways to do it and each has it’s advantages and disadvantages. 
With a DMTD sort of system, you can’t grab “off the shelf” hardware to get things up
and running quickly. Also the isolation / ground loop / spur problem is very likely to 
get you on a DMTD like system with 20 to 30 devices on the same “party line”.

No ideal answer, just a lot of tradeoff’s.

Bob

> On Mar 17, 2019, at 4:48 PM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Sun, 17 Mar 2019 10:58:49 -0400
> Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> The first thing you need (after all the standards) is a way to do precision 
>> comparisons of all your devices. There are an infinite number of ways to do
>> this. Let’s say you buy 26 TICC’s to do the job ( TAPPR needs 25 ordered to
>> get the next batch going so that would solve two problems at once :) ). A
>> PPS from a single source with good short term stability (maybe an OCXO) goes
>> into one side of all of them. A pps from a DUT goes in the other side (yes
>> there are other ways …TAPPR needs that order ….).
>> You then have 26 devices each reporting how a single standard compares to 
>> the “main OCXO”. 
> 
> 
> I would use here a variant of DMTD: Instead of comparing pairs
> of standards, have one offset frequency generator feed multiple
> mixers, one for each standard. This way, the standards can be
> compared to eachother more easily. Downside of this is, that
> the precision of this comparison depends on the stability of
> the distribution of the offset frequency signal. Though, under
> the assumption that ground loops can be kept in check, this
> should be easier to ensure than having pair wise comparisons
> not drifting away too much. When using TICCs, with their high
> measurement rate, I would also go for an offset frequency in
> the order of 1kHz instead of the customary 1-10Hz. This will
> help getting away from the flicker noise region and also give
> a much higher slope of the signal to work with, reducing the
> white noise of the measurement. Additonally, this should
> also give higher precision at tau = 1s, as the system is now
> averaging down from 1ms instead of 100ms (when using 10Hz),
> which could potentially give a boost of a factor of sqrt(100ms/1ms) = 10.
> 
> 			Attila Kinali
> 
> -- 
> <JaberWorky>	The bad part of Zurich is where the degenerates
>                throw DARK chocolate at you.
> 
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