Hi folks,
The other day, I was trying to troubleshoot a 100MHz amaplifier in a piece of equipment ( actually, a Cushman CE-3 Spectrum Monitor ). I was using a 150MHz tektronix scope with a 10X probe. I was getting different results with each measurement, it was driving me crazy.
My friend Bob, the RF guru, said "Your trouble is that you're using the HI-Z input to the scope. For VHF, Hi-Z is crap. It just doesn't work. Especially if you have a pigtail for the ground." Guilty as charged...
He then asked if the scope had a 50-ohm input ( which it does ). "Then just make up a probe with a 450-ohm series resistor, and some little ground clip. That's all you need. It will be stable, and it will work up to about a gig. The impedances in this RF stuff tend to be low anyway, so you don't really need Hi-Z."
Makes sense. Any way to buy a probe like this off he shelf?
- Jerry Kaidor ( snipped-for-privacy@tr2.com )