Path: ...!weretis.net!feeder6.news.weretis.net!usenet.blueworldhosting.com!diablo1.usenet.blueworldhosting.com!feeder.usenetexpress.com!tr2.iad1.usenetexpress.com!69.80.99.27.MISMATCH!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Mon, 08 Apr 2024 23:47:18 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Scope Probes off Ebay Date: Mon, 08 Apr 2024 16:47:18 -0700 Message-ID: References: <4l851jte21egs8mmkqou4proepifknb7v7@4ax.com> <55j51j5n2p9chajruolqrmqs57smippb5t@4ax.com> <6zKQN.497949$ET2.221186@fx12.ams4> <6qu71j1qp2kvre2f0mk8l84haq03u9k3d4@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Lines: 94 X-Trace: sv3-Vx1m4VN+8HRQQrJ8TQ/Lw81VvTfw6tUKy6520q//tJdjnTTOqDOW8nsIvqnhviY2dn3JxJxQv/4TkwV!dKufRWaBj3HPMzZVitJyDxScXgnEQjyrIz2UJdgGNsFiCJN0ilxMy89PwfEk1zHNTJ9LXuDP1Cga!3Z7fPA== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 5658 On Tue, 9 Apr 2024 01:42:22 +0200, Klaus Vestergaard Kragelund wrote: >On 08-04-2024 16:24, John Larkin wrote: >> On Mon, 8 Apr 2024 15:30:57 +0200, Klaus Vestergaard Kragelund >> wrote: >> >>> 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. >> >> We often probe without a ground connection at all, with fet and Z0 >> probes. You get a bit more noise but you see what's going on. >> >> Critical signals get their own "probe" built into the board, with a >> coax connector. >> >> https://www.dropbox.com/scl/fi/jpy8onicfd1yrlzyp8qc2/T660_Phemt_Oscillator.jpg?rlkey=f5uzzmpmc3z6edqz48c47o31q&raw=1 >> >> That's the clock from a triggered LC oscillator. >> >> https://www.dropbox.com/s/674b2w56c0q9orn/Burst_1.jpg?raw=1 >> >> >> SMB, when there's enough room. >> >> >I do that too, also for all PSU rails. And add resistor in series with >the feedback path of PSUs, then it real easy to do gain/phase measurements > >I add 900ohm resistor on the board before the UFL, I guess you do the same? 450 usually, for 3.3v type signals. High voltage dividers are another story.