RE: Differential voltage probes 1

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

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 16:35 28/06/03 -0600, you wrote:
>Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
>
>
>So I am wondering what a good max voltage number and top frequency should 
>be?  We could push the voltage up higher I think, but the frequency will 
>probably just turn out at around 5 to 10MHz.  The high resistance dividers 
>are the problem.  I note Tek drops Z wildly at high frequencies to get 
>higher frequency response...  Note sure that is a great idea...
>
>This type of probe would drop CMRR and all that to "don't care"...

You own a Tek P6015 probe, so you know the lengths that need to be gone to 
if you want to keep a HV divider network flat to within a measly 2%. In 
this application you're trying to do the same, and worse still, to match 
two networks to each other. Using physically small resistors will help you 
by reducing parasitic capacitance and antenna pickup effects, but this will 
also reduce the voltage safety margin.

I think the tradeoffs involved mean that jobs like this would be better 
done by two probes. Probe 1 would be a reasonably fast 10x active 
differential probe, with maybe 500V common-mode capability and at least 
20MHz bandwidth, for looking at microcontrollers, gate voltages, etc, in a 
SSTC.

Probe 2 would be a 1000x passive single-ended HV probe (a cheap clone built 
along P6015 lines and filled with mineral oil) or a 1000x active 
diferential probe, good for 20kV (like the circuit you posted) for playing 
around your conventional coils. The bandwidth of this one only needs to be 
about 1MHz, indeed a low bandwidth might help by getting rid of spark gap 
rubbish.

Steve C.