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NNTP-Posting-Date: Mon, 08 Apr 2024 14:12:58 +0000
From: John Larkin <jl@997PotHill.com>
Newsgroups: sci.electronics.design
Subject: Re: Scope Probes off Ebay
Date: Mon, 08 Apr 2024 07:11:15 -0700
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On Mon, 8 Apr 2024 09:45:03 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:

>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

We get SMA connectors from Shining Star. Excellent.

Custom RF cables from RF Street. Purchasing notes say not to buy from
Lighthorse.