Re: Streamer formation on the scope...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Terry wrote:

> I feed a 100mAp-p square wave in and got this:
> http://hot-streamer-dot-com/temp/02090601.gif
> The data file is at:
> http://hot-streamer-dot-com/temp/02090601.CSV

> The input is in blue as picked up by a 60MHz 10:1 probe.  The top is
> the output.  The output looks nice and stable but feeding the 50ohm
> A33120a's output right into a 1 ohm resistor through about 3 feet of
> coax causes a big spike... 

Yup, you've quite a high ISWR there!  Perhaps a 50ohm termination
would have been better :)

Must be quite a bit of capacitance floating around somewhere to get
a fundamental ringing with such a long period with only 3' coax.

The probe bandwidth looks to be a lot narrower than 40Mhz with a 
pronounced roll-off from quite a low frequency.  Can you capture
a white noise current at a timebase of 1uS/div?  Two traces would be
nice, one with the noise source turned on, and another with the
source off to get the background.  Use a 50ohm load to terminate
the test current, and a 50ohm load at the scope end of the coax leading
from the fibre optic receiver.  That'll take all the cable responses
out of the picture and we'll be able to see the true amplitude response
of the probe (although not its phase response!).

So far it looks as if those ringing signals from the breakout current
could be of rather higher amplitude than the low frequency calibration
suggests.
--
Paul Nicholson
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