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From: Klaus Vestergaard Kragelund <klauskvik@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Scope Probes off Ebay
Date: Mon, 8 Apr 2024 01:04:56 +0200
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On 07-04-2024 18:57, 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.
> 

I did some consulting job recently. One of the guys insisted we buy the 
expensive probes, I carried on with my 900ohms 20:1 10 USD probe. By the 
way, the resistor on the end probe is not sensitive to pigtails, so in 
many cases it's better than the expensive probes