Re: Water probe: signal processing now ok

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Paul Nicholson <paul@xxxxxxxxxxxxxxxxxxx>

Hi Marco,

Thanks for the update.  I've been following exactly the
same lines, starting with the Fiber_vamp.csv file of
27th Jan, and obtain similar waveforms.  The probe
response is in

 http://www.abelian.demon.co.uk/tmp/Fiber_vamp.ift.gif

Marco wrote:
> I came up with this solution:

> - convolution in the frequency space: FFT of input divided
> by FFT of probe, then IFFT to get back to time space

> Inverse convolution in the time domain is very unstable.

The deconvolution is implemented by FFT, division, then inverse
FFT, so I'm not sure where your instability is coming
from - it should be the same as your first solution.  Is there
another method for deconvolution?

> - Hanning windowing to cut the slices: avoids spikes at the
> slice boundaries, 50% overlap to achieve a gain of 1

Yes, a simple and very effective method for chopping long data
sets into manageable chunks for FFT, filtering, inverse FFT,
then stitching it all back together to produce seamless
output.  I use it a lot for processing data from radio
experiments.

> the secondary is indeed responsible for that [100kHz] peak.

Glad that's confirmed.  We need to remove that peak from
the impulse response  (we dont' want to deconvolute that
resonance - it's part of the system being measured!).

What of the resonances at 5.6Mhz and 9.2Mhz?  I believe you
concluded these were genuine probe responses, not coax
resonances?

> Note that the responses are so clean now because we have been
> averaging (within the o-scope) 200 readings of the step.

Are you still using the fiber and video amp?  Can you email me
the latest scope trace data for the step?

> It seems to me like the next step is to switch Thor on and
> to make some measurements at full operation.

Yes, and you'll also need to do some below-breakout firing to
calibrate models.  It will be a major step forward to have some
precision topvolts waveform data.  At last there is a hope for
moving forward on the issue of discharge loading.

--
Paul Nicholson
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