Path: ...!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Klaus Vestergaard Kragelund Newsgroups: sci.electronics.design Subject: Re: Scope Probes off Ebay Date: Mon, 8 Apr 2024 15:30:57 +0200 Organization: A noiseless patient Spider Lines: 62 Message-ID: References: <4l851jte21egs8mmkqou4proepifknb7v7@4ax.com> <55j51j5n2p9chajruolqrmqs57smippb5t@4ax.com> <6zKQN.497949$ET2.221186@fx12.ams4> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Mon, 08 Apr 2024 13:30:57 +0200 (CEST) Injection-Info: dont-email.me; posting-host="0269f4d691e5163a633039893c63d832"; logging-data="3707917"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX190b/qRPloynUBaw6JoVIfiadLYo7uTAAA=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:gKKCJQj5jUV4sKcX0CYqIIBqHAw= Content-Language: en-US In-Reply-To: <6zKQN.497949$ET2.221186@fx12.ams4> Bytes: 4037 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 >> wrote: >> >>> On 8/04/2024 2:57 am, John Larkin wrote: >>>> On Sun, 07 Apr 2024 14:51:29 +0100, Cursitor Doom >>>> 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.