Re: Scope Probes off Ebay

On 08-04-2024 06:40, Chris Jones wrote:

On 8/04/2024 11:36 am, John Larkin wrote:

On Mon, 8 Apr 2024 11:06:52 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:
>

On 8/04/2024 2:57 am, John Larkin wrote:

On Sun, 07 Apr 2024 14:51:29 +0100, Cursitor Doom <cd@notformail.com>
wrote:
>

I never learn. I bought a used "Agilent 500Mhz probe" off Ebay for 50
quid as the highest bandwidth probe I thought I had was a 150Mhz Tek
one. Anyway, I have a large selection of old probes lying around so
decided to check to make sure the "Agilent" one was genuine. Not
surprisingly it turns out it isn't. I haven't calculated what it's
real bandwidth is. I've established it's not as sensitive as the
150Mhz one and that's all I need to know. Whilst I was going through
this palarva, I tested a old probe I came across that I've never used
before and was amazed at the improvement in signal I got with it. I've
just Googled its part number and it turns out it's a 3.5Ghz passive
probe! I never even knew I had one so fast. I would never have ordered
the "500Mhz" one if I'd known I had this forgotten-about one already.
So the fake's going back for a refund and I won't be ordering  any
more probes from anywhere in the forseeable future.

>
The HP54006 is a 6 GHz probe, into a 50 ohm scope.
>
https://www.dropbox.com/s/lxq4ujmkvo755uy/HP54006_probe.zip?dl=0
>
They show up on ebay now and then. There's one now, asking $150.
>
You can make your own with some of those Caddock resistors. The
Caddocks have some magical recipe. And unlike a fet probe, they are
hard to damage. I use them to probe 7 ns 1400 volt spikes in my
Pockels Cell driver.
>
And you can do a GHz at least with a 1-cent axial or mini-MELF or 0805
resistor on the end of a coax. 450 ohms makes a 10:1 probe. Fast
circuits are often low impedance circuits and don't mind a 500r or 1K
load.
>

>
>
Which Caddock part number?

>
In the zip file.
>

  Thanks, I only looked at the pdf before. For usenet posterity the zip file contains Agilent document 54006-90002 and a photo of a probe made from a SMA connector with a resistor marked MD1248 950 1%, and a packet of resistors marked CADDOCK Part No. 0699-2371 (MD1247) Rev B Model MG680 Resistance 450 Ohm Date 12-7-88 Date Code 8845 amongst other things.

This is comparison with sub pF probes vs just a resistor/coax. Seems the performance from the coax is very similar to high end active probe. From:
http://www.sigcon.com/Pubs/straight/probes.htm
Notice, that you can
have a rather long pigtail on the coax probe and it won't affect the signal.