[time-nuts] On some pitfalls of the dual mixer time differencemethod of h...

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Oct 1 19:25:46 EDT 2006

Magnus Danielson wrote:
> From: SAIDJACK at aol.com
> Subject: Re: [time-nuts] On some pitfalls of the dual mixer time differencemethod of h...
> Date: Sun, 1 Oct 2006 13:53:57 EDT
> Message-ID: <c80.290792e.32515ab5 at aol.com>
>> Hello Ulrich,
> Ulrich and Said,
>> the latest generation of TSC intruments (the TSC5120A for example) uses a  
>> new strategy: they use four ADC's to sample and cross-correlate two oscillators  
>> completely in software. All the mixing etc is done in the software domain. 
>> That  makes for cheap hardware, and works quite well. They had a tutorial about 
>> this  at this years UFFC in Miami.
> You also get some insight when picking up the manuals from their web. It is a
> quite different animal in implementation than the old hardware correlatetors
> are, which has both benefits and drawbacks. It is however a very modern
> approach indeed.
> Cheers,
> Magnus
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Interesting as the techniques employed may be, the resultant performance 
is still inadequate for characterising state of the art oscillators.
The instrument phase noise floor is higher than that specified for 
current low noise (but not necessarily low drift) crystal oscillators.

The Allan deviation of current state of the art cryogenic sapphire 
oscillators is more than an order of magnitude lower than the noise 
floor of these instruments.


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