TSSP: List Archives

From: "Terrell W. Fritz"
Date: Sun, 27 May 2001 14:34:18 -0600
Subject: Re: [TSSP] Topics on non-linear effects

Hi Paul,

At 10:58 AM 5/27/2001 +0100, you wrote:
>Terry,
>
>Excellent scope traces - packed with information - its going to
>take we a while to work through these.  The discharge current
>waveform looks pretty linear at first glance, with the 3rd harmonic
>around 20dB down in the FT.  On close inspection you can see
>some distortion to the trace, but clearly not a vast amount. 
>
>There looks to be an asynchronous component, probably the
>3/4 wavelength mode getting excited a little. I could do with a
>narrow band view of the 0-2Mhz region, could you capture a trace of
>about 800 cycles of the current waveform at around 0.2uS or 0.25uS
>per time step?  

Yep.
http://hot-streamer.com/temp/TerryCW/2001-5-27/Tek00000.gif
http://hot-streamer.com/temp/TerryCW/2001-5-27/TEK00000.CSV


>
>Interesting bit of fluff at around -7.6uS in TEK00002. A burst of
>ringing there, at around 74Mhz - wonder where that came from?

The voltage antenna has a bandwidth of 100MHz as does the scope.  The fiber
optic has a BW of 2MHz.  The fiber can go to 40MHz but the signals are so
low noise swamps them.  I could change out the sense resistor if needed?

Who knows what all the subtle things mean.  That fuzzy ring at 500nS in:

http://hot-streamer.com/temp/TerryCW/2001-5-26/Tek00003.gif

Really should not have been picked up buy the fiber optic current probe...

>
>Seems to me, the initial impression is that the prospects for a time
>averaged impedance look good.

I have used 220k ohms + 1 pF per foot of streamer in many models and it
always seems to work (disruptive coils).  All the resulting voltage and
current effects seem to work out well.  So perhaps a simple impedance will
work well as opposed to the much more nasty time varying case...

BTW - I'll work on getting the base current thing set up today.

Cheers,

	Terry

>
>Cheers,
>--
>Paul Nicholson,
>Manchester, UK.
>--


Maintainer Paul Nicholson, paul@abelian.demon.co.uk.