Re: HV Oscilloscope probe (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 28 Aug 2007 21:17:41 -0700
From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>, tesla@xxxxxxxxxx
Subject: Re: HV Oscilloscope probe (fwd)

At 08:02 PM 8/28/2007, Tesla list wrote:

>---------- Forwarded message ----------
>Date: Tue, 28 Aug 2007 18:57:48 +0200
>From: Herwig Roscher <herwig.roscher@xxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: HV Oscilloscope probe
>
>
>Hi coilers,
>
>As I have received no comments on my question, I assume that it has
>not made its way to the list. Therefore I would like to repeat it:
>
>"For measurements of HV and RF I have acquired a Modular Oscilloscope
>Probe
>TT-HV 250.
>
>Attenuation 100, Input impedance 100 MOhm/4 pF, Bandwidth 300 MHz,
>Risetime 1.2 ns
>
>Maximum input voltage  2500 Vp - but only up to 1 MHz. Above this
>frequency the permitted voltage is specified to fall logarithmically
>down to 6 v(!!) at 300 MHz.

Probably because it forms a capacitive divider.. the 4pF starts to be 
pretty low impedance (132 ohms at 300 MHz), and working into the 
usual 1Meg paralleled with 15-20 pF, it's only a 10:1 divider.


See, e.g., http://www.highvoltageprobes.com/faq.html for a discussion 
of HV scope probes.