[R-390] More Voltage Divider Stuff

Barry n4buq at knology.net
Mon Mar 19 19:47:48 EST 2007


A few days ago, I posted some info on my 50:1 voltage divider project.
Someone posted that there's a possibility that the 1-ohm resistor in it
might have some inductance, thereby throwing off the calculations.

I wondered about this, so I set up a little test.  I connected one input of
the dual-trace scope to the same point where the signal generator is
connected to the divider.  I connected the other input to the divider point.
The generator has a high-output level so I was able to drive the scope to a
nicely-sized wave forms.  I set the "high" input to 1V/div and the "low"
input to 0.02V/div.  The image below is at about 1.6mc.

http://www.knology.net/~thelanding/R390A/traces.jpg

Note that both waveforms are pretty much identical in amplitude.  (The upper
one doesn't appear to touch the upper line, but I didn't quite have the
bottom of the waveform on the horizontal line either.)  In face, if I move
them together, they appear as one.

Just to verify things, I switched the inputs and reversed the V/div
settings.  The results were exactly the same.

I assume that if there is any inductance at play here, it is quite
negligible.  I wish my scope had a higher b/w, but the TEK 561A with the
plugins I have start falling off rapidly at this frequency.

I wonder if it is worth checking at higher frequencies with a better scope?

Barry - N4BUQ



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