Re: Replacing cable on P6075A probe


Tom Lee
 

Not quite right to compare 250 to 10Meg and declare 200 to be therefore ok. By that logic, zero ohms should be just fine, too. Yet, Tek went to the trouble to use resistance wire. Clearly there's a reason!

The purpose of the resistance wire is to damp out reflections due to mismatch. There's a Goldilocks optimum for each length that balances bandwidth against aberrations. If you deviate from that balance, either parameter degrades.

That said, you're probably not going to notice any dramatic change. But if you had before and after measurements, you'd see a difference.

Tom

Sent from my iThing, so please excuse the terseness and typos

On Nov 17, 2020, at 5:24, "Brent W8XG" <brent@pwg.net> wrote:

No, I did not do a YouTube video. But I've seen one out there. I didn't have a replacement cable or other parts. I cut my cable off at both ends as close as I could to the strain-relief parts, then tested the cable. It tested good, so I knew I'd cut out somewhere the break. I used the typical wire strippers to remove the insulation. I was very slow and methodical. But I was surprised at how fine that wire was. Then I had to clean out both strain relief's, with a Dremel. Once cleaned out, I pried them open just a little, to be able to slip the cable in and then crimp.

So my cable is now a little shorter. The 250 ohm's is likely about right given the size of the wire, but I didn't measure it. So my cable might be 200 ohm's now. But with the 9k resistor in there to make it a 10x probe, I doubt it matters much.

I don't know what the grommet is for. Maybe it's to slip over the cable and then crimp to become strain relief??

Regards,




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