Homebrew HV hiZ scope probe

R=252.5e-3\n+)

It has been a loooong time; Tektronix made two high voltage probes - one with a significantly higher voltage rating. The one i have _did_ have the liquid inside but that has slowly leaked out over the ages; it is the P6015 rated at 20KV, 40KV peak. I think that is the top end in voltage.

Perhaps, but us mortals with a limited budget cannot order umpteen thousand feet of coax with a resistive center. The P6015 used ten feet of coax with resistive center (direct quote from manual). Cannot say what its resistance is..i read 657 ohms end-to-end on the cable, and the schematic states 150 ohms 10% at probe end, implying the coax center is about 500 ohms (~5 ohms per foot).

Since you specified 75 ohm cable, the R should then be 75 ohms instead of 60 ohms (pickie).

Yes...all it takes is a lot of $$ for the special order. Unless one is VERY fortunate to find it in a surplus house or willing to rat out the cable from a P6015..

Did a Baby Bird (GooGull) snoop..NGK resistive wires "utilize a construction method known as "variable pitch" wire winding to create resistance to radio frequency interference. NGK wires have a lower resistance than conventional carbon core wires (8k ohm/meter vs. 16k ohm/meter)." So these "better" spark plug wires have a "mere" 2.4K/foot resistance, which exceeds a desirable amount by about an order of magnitude. Excellent suggestion, however..

SACRILEGE!!!

If you were a true tree huger, you _would_ "pine" for them..

• Check.

That is exactly what was used as a reference by Fred Abse in his Spice listing (Belden 83265 is RG-178B/U 50 ohms) .. but data used was for the RG179 which is 75 ohms but otherwise rather similar.

Robert Baer wrote in news:_SGjs.67$ snipped-for-privacy@newsfe09.iad:

CUT

Any car repair shop. Used to hook up spark plugs.

He's just another sap...

On a sunny day (Mon, 29 Oct 2012 18:21:22 -0800) it happened Robert Baer wrote in :

Personally for a one case, I would take normal coax, pull the center conductor out, and insert thinner resistance wire. Should work for length of 1m or there about.

Not sure if that helps for your case.

Yeah, like dragging the center conductor out of a meter long piece of coax is an easy task, much less feeding another back through.

Standard RG-8 center conductor dielectric strength is 1.5kV.and they are not easy to get out. Fairly tightly bound to the core media.

Probably cheaper to find and get the right stuff.

Not any more. It has derated itself to about 12kV. It won't do 40kV anymore without the fluorocarbon.

If you can get the 114 from somewhere, you can recharge it. See the manual.

Then do what I did, resistors at each end.

Wrong. The value of 60 ohms was empirically determined from an .ac analysis, with the resistor values stepped. See my LTspice listing, all the necessary information is there, just uncomment the .step param card, and comment (or delete) the 60 ohm R parameter. Pick the value which gives the smoothest, flattest rolloff, at the HF end. Try without any resistors, too, you'll see what I mean about resonance.

The value of R is *not* the Zo of the cable (which is complex,anyway).

It's not nice to needle people like that.

DuPont (Ithought)(apperently 3M now) FC-40 also works. "Fluorinert"

Is "people like that" referring to the needling method or the "way" the person is?

If you follow the logical tree, I guess the answer is "both."