Path: ...!weretis.net!feeder6.news.weretis.net!feeder8.news.weretis.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: Tue, 9 Apr 2024 01:42:22 +0200 Organization: A noiseless patient Spider Lines: 87 Message-ID: References: <4l851jte21egs8mmkqou4proepifknb7v7@4ax.com> <55j51j5n2p9chajruolqrmqs57smippb5t@4ax.com> <6zKQN.497949$ET2.221186@fx12.ams4> <6qu71j1qp2kvre2f0mk8l84haq03u9k3d4@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Mon, 08 Apr 2024 23:42:21 +0200 (CEST) Injection-Info: dont-email.me; posting-host="25a0df557d28e34d12509c1e8ade0efb"; logging-data="3993199"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/qxBHgt5XGUEiexafJN8hCW9P8OFqd5tk=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:nPHJp1TEhH3rbPXNYNadaPyALd0= In-Reply-To: <6qu71j1qp2kvre2f0mk8l84haq03u9k3d4@4ax.com> Content-Language: en-US Bytes: 5194 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?