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ok thanks, unfortunately totally different layout to my A9 board. the manual isn't very helpful at all.

Yes. The typical instrumentation grade RF source (eg. signal generator) can be modeled as an ideal voltage source in series with an ideal 50 ohm resistance (impedance). It is a desirable condition in

I think the A9 CC Jumper is in position E33-E34. See the picture attached but I am not 100% sure because there were different A9 CPU boards for those series and they have slightly different layout.

A BNC sleeve is exactly what it sounds like it is. It fits over the bare probe tip, making a press fit connection to the inside of a female BNC connector so that you can make a good, albeit high

The problem with trying to do this with two probes in parallel (using a BNC T piece) is that you will end up with double the loading so I'd expect this test method to be doomed to failure if the aim

Do you have the adjustments tab which shows which jumper is the A9 CC jumper ? the manual I have just keeps saying move the A9 CC jumper, but doesn't actually say anywhere which jumper that is on the

Sorry - need a bit of clarification here. "BNC adaptor sleeve" - what is that? Does it fit over the probe tip or something?

I'll try that, Robert, thanks. It'll probably not be today owing to time pressures but I'll report back here in due course...

The 10073C should have come with a BNC adaptor sleeve. So should your "good" probe. To eliminate all loading and source imedance issues connect a BNC T to the signal generator output and directly

It's made for HP scopes and logic analyzers like the 16500C 16700B... Could be...

Yes, it's a Tek 2465A; the highest bandwidth scope I have.

Thanks for the offer, JMR, I'll see how I get on with some other tests before imposing on you. I have asked a colleague to measure the probe impedance at DC and it's a whisker over 2.2M ohms, so

It's worth adding a 10dB pad at the sig gen output to make sure the source Z is close to 50R and then the effective source impedance driving the probe will be about 25 ohms with the output termination

Also, when testing with your sig gen you need to terminate the sig gen with a good 50R load. I'd recommend using a short test PCB with some 50R microstrip on it with a good 50R termination at the far

I have no access to the probe until tomorrow morning. I have not as yet tested to check if it's 2.2M ohms, which sounds like a very simple quick and dirty test and would eliminate it as real or fake

The other thing to do is to make sure you are compensating it correctly. Also, you should see quite a difference in the response of the compensation if it is a genuine 10073C compared to a regular 10M

Oh yes, didn't take that into account, of course. Raymond

I recommend measuring it to see if it is a fake probe? A fake version might have a 10M input. If it is 10M then it's safe to assume it's a fake without doing any more tests. Hopefully, Jinxie already

Except that at 500MHz, a source sees only the 26Ohm, not 2.2MOhm (nor 10MOhm). What would the benefit to the OP be of testing that the 10073C's input resistance is according to its DC spec? Raymond

At 500MHz, it's not completely insignificant that the 10073C is a 2.2M probe. By designing for a 2.2Meg input divider (and not a 10Meg divider)? it makes it much easier to achieve good compensation