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.