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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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