No subject


Wed Dec 3 18:34:25 UTC 2008


full-precision sine function.  Fill the drive file with multiple copies of 
this one-cycle file placed nose-to-tail.  Feed to soundcard hardware.  If 
the soundcard has some kind of buffer and buffer-repeat function, one can 
eliminate generation of the big file.

This kind of software approach would eliminate a whole lot of uncommon 
hardware, so we really ought to see if it can be made to work well enough 
for our purposes, as it would be such a big win.


> To broaden participation we need to broaden the scope of the project to
> include dual mixer system with statistically independent test sources as
> well as the more specialised case where the 2 input frequencies differ
> only in phase.
> 
> 1) Evaluate sound cards for suitablility.
> Initially use simple less stable sources and follow up with more stable
> test sources for the more promising cards.
> Need to measure crosstalk, temporal instability of interchannel phase
> shift, system noise etc.

Generally agree, but there is that undefined elastic term "suitability" 
again.

 
> 2) Develop robust algorithms for phase extraction.
> Use the data produced by the less stable sources and that produced by
> the more stable sources

Agree.

 
> 3) Repeat testing using a dual mixer system complete with offset LO.
> Test frequencies identical to evaluate system noise floor.
> 
> 4) Repeat testing using a dual mixer system complete with offset LO.
> Test frequencies differ to help the effect of residual crosstalk and
> other artifacts.
> 
> 5) Split the project into 2 branches:
> A) where mixer inputs differ only by a phase shift to be measured.
> Useful for measuring effect on ADEV of various components and their
> phase shift tempcos etc.
> 
> B) Where the mixer input test sources are statistically independent.
> Useful for measuring pairwise source ADEV etc.

Although these are likely future directions, we probably should focus on 
your Tasks 1 and 2 for now, and see how much we can wring out of commonly 
available soundcards.  Tasks 3 et seq may change depending on the results 
of 1 and 2.

Our two Task 1 items appear to be compatible.

Joe



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