Cheap P6100 probes = junk?

[eccerr0r]

Re: Cheap P6100 probes = junk?

I chanced upon getting an official Tek P6120 x10 probe. Alas it's only a 60MHz probe, but I can assume that Tek really means 60MHz. I tried hooking up a P6100 probe to Ch.1 and a P6120 to Ch.2 and tried comparing the two...

Unfortunately no fast edge to check rise time...

Alas other than mucking with the compensation a bit to match my scope... can't really tell much difference using the calibrator output (not unexpected...). The calibrator output doesn't really have a fast rise/fall time.

[eccerr0r]

Re: Cheap P6100 probes = junk?

ALLRIGHT... I built an avalanche pulser (breakdown testing of a 2N3904 and 150V supply, 20pf cap discharge) on a breadboard, and tried measuring rise time with the cheap china probes... On my Tek 2465, I got... 1.96ns risetime. This is scope + probe + breadboard...

My 20MHz scope... Being non-digital and 100ns/div is the fastest sweep, was tough to tell. I estimate around 20ns rise time, maybe less.

I also have some Tek P6120s which are rated 60MHz probes.
Rise time = 1.88ns on the Tek 2465...

What the...

Well at least the china P6100 probes are almost as good as the P6120's.

[stj]

Re: Cheap P6100 probes = junk?

it's possible the tek probes can go over-rating,
and the chinese meet spec.

i'v seen people on EEVblog using 100MHz scopes to view upt 300MHz signals - although not perfectly!

[eccerr0r]

Re: Cheap P6100 probes = junk?

Well if the probe isn't rated for 300 and you run it at 300, it just means it's attenuated. Trouble is, indeed, it's a bit iffy to use them because now the 300MHz component is attenuated but the 100MHz component isn't, so your waveform looks a bit distorted from reality (!)

But it looks like in Tek's world with their screwy formula,
P6100 = 1.96ns => 180MHz
P6120 = 1.88ns => 194MHz (!)
20MHz scope = 20ns => 17.5MHz ... At 17ns it would be 20.6MHz, but in any case the scope is limiting bandwidth, not the probe.

[eccerr0r]

Re: Cheap P6100 probes = junk?

Hmm... and my third scope (DSO), using its onboard rise time measurement, says ~1.6ns rise with the cheap china probe (!). However this DSO is using multisampling to get a waveform (Tektronix 2440: 300MHz frontend, 500MS/sec backend). Ah... the conveniences of a DSO...

All in all I guess other than the possible crappy construction issues that will cause the probe to disintegrate on you, the P6100 does indeed meet 100MHz spec. Thumbs up. I do wonder if there are "clones of clones" of these probes (seems like there are multiple versions) - and whether they are up to snuff.

Hmm. I may have to build the pulser into a self contained unit, hopefully to reduce parasitic inductance to stop ringing and to test other things later. Though I will have to figure out how to squeeze in a power supply for it...

[eccerr0r]

Re: Cheap P6100 probes = junk?

Pictures!

My Tek 2440, Tek 2465, and 20MHz VuData scope output from the pulser and the cheap china probe (P6100)

I don't know why the 2440 rings so much worse than the other two...Something weird going on. Termination was off on this run but didn't help much with it on.