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From: Jeroen Belleman <jeroen@nospam.please>
Newsgroups: sci.electronics.design
Subject: Re: Scope Probes off Ebay
Date: Mon, 8 Apr 2024 09:45:03 +0200
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On 4/8/24 00:11, Cursitor Doom wrote:
> On Sun, 07 Apr 2024 12:08:43 -0700, John Larkin <jl@997PotHill.com>
> wrote:
> 
>> On Sun, 07 Apr 2024 18:14:25 +0100, Cursitor Doom <cd@notformail.com>
>> wrote:
>>
>>> On Sun, 07 Apr 2024 09:57:13 -0700, John Larkin <jl@997PotHill.com>
>>> 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.
>>>
>>> Funny you should say that, but the 3.5Ghz probe I mentioned (a Tek
>>> P6056 to be precise) has a fragile resistor assembly in the tip
>>> according to the datasheet and it's easily damaged by rough handling.
>>> I'd be very interested to know what the secret sauce is in the
>>> Caddocks and why they're more robust than whatever Tek used in the
>>> P6056.
>>>>
>>>> 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.
>>>
>>> Many years ago when I was somewhat impecunious, I used to improvise
>>> like that, but these days I prefer to just buy whatever I need ready
>>> made. Some of those top-end RF patch cables can be ruinously expensive
>>> to buy ready-made, but what are you gonna do? No matter how good you
>>> are with terminations, you'll never emulate the quality standard of a
>>> properly made, high quality patch lead. When you're as ham-fisted and
>>> half-blind as I am, it's a no-brainer to buy 'em ready-made!
>>
>> Amazon has some crazy cheap coaxial jumpers and SMA and SMB connectors
>> and adapters. All the ones I've got so far have been fine. For bench
>> work of course, not production.
> 
> What do you mean by "fine"? How did you go about characterising them
> and what were you looking for specifically?  IME you get what you pay
> for and cheap connectors are very seldom worth it. Buy cheap, buy
> twice as they say.

Not necessarily. I used to buy phase-matched sets of SMA cables
from Huber & Suhner. Then, one day, because H+S did not reply to
a new request for a quotation, I got them from JYEBAO in Taiwan
via a French representative. They were cheaper *and* better.

Jeroen Belleman