[Test-Equipment] Tek P6057 question: Test-Equipment Digest, Vol 85, Issue 19

[Jeff Furman]

Ron, I can't speak specifically about this probe, but generally, you can't 
get meaningful results at 1 Ghz if you use a ground wire. There should be 
a ground ferrule right at the tip for a very short ground connection, or 
possibly mating to a pcb mounted coax connector just for probing. You 
might have found some of these minimal connectors buried at the bottom of 
probe pockets.

Just using the specs, my reactance chart suggests the reactance of 1pf at 
1 Ghz is around 158 ohms. The resistive value, 5K ohms is a high value 
compared to 50 ohms, so, this probe might be used for bridging 50 ohm 
lines (158 ohms reactance is only 3x Zo here.) This might be just 
tolerable if you're desperate to see a signal.
As orders of magnitude go, a 3.16 or greater ratio starts to look like a 
factor of 10 on a log scale (3.16 is 'only' 5Db down from 10.)

I suppose this probe is used with the scope input set to 50 ohms rather 
than 1 Meg ohm (5k/50 = 100.)

I assume this is a passive probe which is likely 10x cheaper than an 
active probe with much higher input impedance. I suspect this is at the 
practical limit for passive probes, I doubt a x1000 passive probe could 
have a 0.1pf input capacitance, but rather still near 1pf.

73, Jeff AD6MX


>
> Message: 3
> Date: Sun, 29 May 2011 11:44:32 -0400 (EDT)
> From: bonddaleena at aol.com
> Subject: [Test-Equipment] probe question
> To: TekScopes at yahoogroups.com, test-equipment at mailman.qth.net
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> Hi. While going through my Tek probes, I came across a strange one. Although the P6057 was not listed in the Tek chart I found on the WWW, I found several descriptions for it.
> It's:
> 100X
> 5K ohms
> .5 Watts
> What's puzzling is there is no ground wire. It has a VERY low capacity (around 1pF), and it's supposed to be good to 1 GHz.
> I don't know if there is a part missing. It doesn't appear so and the description states no grd ref. It DOES have an "IDENT" button.
>
> Any help out there?
>
> ron
> N4UE
>