x1 'scope probes

A FET probe is better still. I got a couple of Tek P6201s in good shape off eBay for $60 each a few months ago.

Cheers

Phil Hobbs

Yeah, but.... Is there any use to a x1 probe?

I had* this old 'big' TEK x10 probe that only had 8.8pF of C. Now all the new little x10 probes that come with scopes are ~16pF.

George H.

I think it has to do with flat response across the bandwidth. A piece of wire can serve as a "probe," (#22 or #24 will plug right into a BNC center conductor jack, I don't recall which) but you might get artifacts at some frequencies because of strays and stuff.

It's been many years, but I think if you stick a resistor at the end of the raw coax, and some kind of capacitor in shunt with the resistor, it can flatten out the response.

Try each of these on your calibrator output, (1X probe, naked wire, naked coax, coax with a series resistor, and coax with a shunted series resistor) and see what the corners look like - that should give you your answer.

If your 'scope doesn't have a calibrator, then slap together an astable and see what _its_ corners look like. :-)

Have Fun! Rich

Scope probes use special "coax", namely tiny resistance wire in a big tube. This is supposed to keep the capacitance down and reduce ringing.

A short coax can be better than a 1x probe, especially as regards RF pickup.

As Phil says, fet probes are great. Much cleaner and almost no loading. They even work well without a ground clip. They sometimes work well with the tip just near the signal.

John

As old-time circuit columnist Tom Kneitel used to say, 'Scope probes are marked "10:1" because they ten to one away when you aren't looking.'

I can't remember the last time I used a 1x probe. I have a few that have 1x/10x slide switches, but they're always on 10x. Maybe you could havn one out as bait to catch the guy that walked away with your good one. ;)

Cheers

Phil Hobbs

That's a good idea (looking with the 'scope calibrator), I'll give it a whirl.

Hmm everything looks the same...(I used a function generator and not the 'scope cal terminals.) OK enough screwing around. It seems to me that a x1 probe is no better than a piece of coax.

George H.

Ahh, a bit of capacitve coupling. I've recently been wrapping a bit of insulated wire around the pin of an opamp that I want to probe. Then a square wave on the wire gives you a pulse of current into the circuit. You can send in a triangle wave and get a square wave of current. Very nice for seeing if there is any difference between the light response and electronic response of a photodiode circuit.

Sure you can just tack a small cap on instead, but not as much fun as a piece of wire.... It's half a gimmick!

George H.

I have seen a tutorial on scope probes that described all the whys and hows, I think it was Techtronix, but could have been HP. The paper describes probes made with coax for low impedance and high freq probes. Good article, saved it on the harddrive that died :-) I'm sure it is still available.

I've been searching, haven't found the one I remember, but see these.

I bought these 100 MHz probes on Ebay:

Will those work on any scope?