// #eevblog — 2019-08-10
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00:01:57 <DHess_US> I'd just be happy of LED bulbs lasted more than 6 months here. I'm going broke replacing them.
00:02:48 <steve30> I bought some Philips ones for the kitchen in 2013 which are still going strong.
00:02:54 <steve30> But back then they were £10 each.
00:03:39 <DHess_US> CFL's and incandescents dont' last any longer. But at least the incandescents were less expensive.
00:38:46 <ifishtoo> looking for 1:1 50ohm probe. Found some old used hp stuff on ebay. Does anybody know if we can get affordable/cheap after market 1x 50ohm probes anywhere?
00:50:52 <DHess_US> Well, this is annoying. I've been spraying my wool socks with DEET in the mornings and now the tops of my feet are getting itchy and breaking out. I had to wrap my big toes in gause before putting my socks on.
00:51:08 <DHess_US> ifishtoo, there is no such thing.
00:51:31 <DHess_US> If you want a 1:1 50 probe, then it is called a piece of 50 ohm coaxial cable.
00:52:19 <DHess_US> 1:1 active probes exist but they are not generally 50 ohm inputs. You can always add a feedthrough termination to one.
01:16:23 <ifishtoo> Acutally it is called a low-z passive divider probe. I did not know it was thing until a few hours ago. I watched a video on eevblog about measuring ripple on a smps.
01:17:16 <ifishtoo> Another one about tracking down the source of common mode interference.
01:18:40 <ifishtoo> Used in pairs, a-b channels. Invert channel b.
01:19:08 <DHess_US> ifishtoo, you can't have a 50 ohm passive divider probe which is 1:1 because that is no division.
01:19:32 <DHess_US> Or rather, a 1:1 50 ohm probe is a length of coaxial cable.
01:19:57 <ifishtoo> Go watch the videos. I don't know what I am doing enough to argue with anybody.
01:20:08 <DHess_US> A 1:10 low-z passive probe is a 50 ohm coaxial cable with a 450 ohm resistor in series at the probe tip.
01:21:28 <ifishtoo> It is a 50ohm pass through terminator ant the input, a length of coax, another 50 ohm resistor very close to the probe tip.
01:21:29 <DHess_US> 1:10 high-z passive probes which are commonly used to measure ripple and noise on power supplies use a special coaxial cable which has a controlled resistance per unit length but the series resistance is insignificant compared to 1 megohm making them 1:1.
01:22:00 <ifishtoo> here is the thread. https://www.eevblog.com/forum/testgear/fifty-ohm-probes/
01:22:08 <DHess_US> That would make a 1:2 low-z probe
01:23:10 <ifishtoo> Here is the probe design http://www.emcesd.com/1ghzprob.htm
01:24:13 <K> hm, doesn't 50ohm business usually mean you have a bnc connector to connect your scope to?
01:24:17 <ifishtoo> https://www.ebay.com/itm/Tektronix-Generic-1-1-Probe-with-Hook-Attachment/264232935339?hash=item3d85829fab:g:jZ4AAOSwqD5chPNl:sc:USPSPriority!97301!US!-1
01:24:30 <K> i.e no poking the pcb
01:24:33 <DHess_US> Your second link is a 40:1 probe
01:25:31 <DHess_US> The ebay link is a high impedance probe like I described.
01:26:23 <DHess_US> Ebay crashed my browser. Give me a couple minutes here and I have a link for you to read about probes.
01:26:48 <ifishtoo> http://hpmemoryproject.org/an/pdf/scop_probe_cat1988.pdf
01:28:36 <DHess_US> For power supply ripple, 1x high impedance passive probes are usually the way to go. They work great in add and invert mode which is recommended in the ATX power supply specification.
01:29:00 <DHess_US> There are better ways but that way is the most available.
01:30:00 <DHess_US> Incidently for calibration of add and invert mode, start off connecting both probes to the same point and then adjust the gain of one channel for minimum signal. This matches the DC gain of both channels for maximum common mode rejection.
01:31:10 <DHess_US> Tektronix wrote a book called "062-1146-00 - Oscilloscope Probe Circuits - November 1969" which you can search for online.
01:32:24 <ifishtoo> Agreed. But the better way involves the purchase of a low voltage differential probe. Spendy.
01:33:15 <ifishtoo> Here is the video where dave shows how to use two 50 ohm probes in differential set up. https://www.youtube.com/watch?v=Edel3eduRj4&t=1826s
01:33:58 <ifishtoo> Sounds like a good book. Thanks.
01:34:49 <DHess_US> The problem with low voltage differential probes is low common mode voltage range which makes it difficult ot use them for power supply noise measurements.
01:35:06 <DHess_US> They are the best way if you can do it.
01:35:37 <DHess_US> Personally I use a Tektronix 7A13 with a pair of x1 high impedance passive probes or a 7A22 if up to 1 MHz is acceptable.
01:36:21 <DHess_US> But even the +/-10 volt common mode range of a 7A13 is not enough for a 12 volt power supply.
01:36:28 <DHess_US> And that is exceptional.
01:37:06 <ifishtoo> The probe I meant to link to on ebay was an hp 10026a. It is in the document link i Posted above.
01:37:13 <DHess_US> Some differential probes support an AC coupled mode. Or you can AC couple externally.
01:37:34 <ifishtoo> So you are using 1mohm 1x probes in a-b mode?
01:37:57 <DHess_US> I've done that also. It works great with some oscilloscopes but the common mode voltage limit still applies.
01:38:15 <DHess_US> So you either need to AC couple or live with much reduced sensitivity.
01:38:52 <DHess_US> Most oscilloscopes only have an input common mode range of 10s to 100s of millivolts.
01:39:13 <ifishtoo> You said " Tektronix 7A13 with a pair of x1 high impedance passive probes or a 7A22 if up to 1 MHz is acceptable. " What is a Tektronix 7A13 ?
01:40:33 <ifishtoo> 'Never mind. I see it. The only plug in module we have is a 1a1 dual trace.
01:41:12 <DHess_US> The 7A13 and 7A22 are essentially differential probes which connect to common high impedance passive probes.
01:41:46 <DHess_US> So with a pair of x1 high impedance passive probes, they become a low voltage differential probe but with limited bandwdith.
01:41:56 <DHess_US> But a 7A13 is plenty fast for power supply measurement.
01:42:40 <DHess_US> YOur HP link doesn't say anything I did not say.
01:42:48 <DHess_US> A 1:1 50 ohm probe is a piece of coaxial cable.
01:44:23 <ifishtoo> maybe I can find a letter plugin model W 23mhz Diff Comp for our 585a
01:45:36 <DHess_US> There is a good chance.
01:46:33 <DHess_US> I think the one you want is the 1A5.
01:47:50 <DHess_US> I have a 545 and a 547
01:48:03 <DHess_US> But only CA and 1A1 plug-ins.
01:49:06 <DHess_US> But the 1x high impedance passive probe way with add and invert mode works. Get a pair of big film capacitors to put on the tips for AC coupling if you need a response lower than 600 Hz.
01:52:32 <ifishtoo> okay. The ic on this chinesium boost converter is supposed to be at 15khz.
02:04:58 <ifishtoo> We have the type 82 adapter so we can run letter series plugins
02:05:53 <ifishtoo> Whats the difference between a differential amp and a differential comparator?
02:06:50 <ifishtoo> Oops . type 81 adapter.
02:12:14 <DHess_US> Nothing really. Differenital comparators are also differential amplifiers.
02:12:31 <DHess_US> The difference is that a differential comparator also has an internal reference for slideback measurements.
02:13:06 <DHess_US> So you can use them to make precision voltage measurements.
02:21:51 <ifishtoo> bye for now.
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09:01:04 <EEVBlog> New EEVBlog Tweet: Some intern-bot at @mashable has just gone and dug up 5 year old debunked tech and mashed a video together (see what I did there) to make it look like they are producing content. You pay people at Mashable to produce this crap? LOL https://t.co/fNJmFlXeZS https://t.co/acaWxcd5je
11:04:44 Quit: ThunderSqueak_ ([email protected]) Quit: Leaving
11:42:16 <EEVBlog> New EEVBlog Tweet: Random pcb found in the middle of a field https://t.co/GP2GJii2Ta
12:28:23 <Halcyon> Morning all
12:28:28 <Halcyon> Well... afternoon
13:09:58 <Ampera> hi Halcyon
13:09:59 <Ampera> how do fren
13:15:43 <Halcyon> Im good
13:15:50 <Halcyon> Had a good sleep in, didn't get up until midday
13:16:04 <Ampera> you're turning into me
13:16:14 <Halcyon> Hehe sort of. I've had a long week, needed it
13:16:26 <Ampera> soon you'll be crying yourself to sleep, staring at an empty monitor for hours on end, and eating plastic crap
13:16:32 <Halcyon> Hahah never
13:19:51 <Ampera> good, I don't think you could handle my pain without killing yourself
13:19:58 <Ampera> and I don't want to see you die, I want to see me die.
13:20:17 <Halcyon> Aww that's one of the nicest things you've said to me :P
14:55:38 <EEVBlog> New EEVBlog Tweet: RT @lukeweston: That’s a cute idea - just an offset dish, no electronics, no power. Phone sits at the offset focus. It’s pointed at Alice S…
16:39:22 <EEVBlog> New EEVBlog Tweet: The new parramatta stadium is pretty impressive https://t.co/24jLrtwX38
18:09:08 <steve30> hi
19:37:41 <damian> what's the nicest thing i've ever said to you Halcyon
19:37:44 <damian> hey steve
19:59:12 <Halcyon> damian: I think you showed me your penis?
19:59:17 <Halcyon> I'll take that as a compliment :P
20:25:47 * steve30 hugs Halcyon
20:30:17 <Halcyon> Awww hi Steve :)
20:31:49 <Halcyon> DogWomble, go to your voice channel
20:34:38 <steve30> Grandma had a power cut yesterday, so we just had to go and set the clock on the oven for her
20:34:50 <Halcyon> Naw
20:35:00 <Halcyon> Want to join us in a game of Cards against humanity Steve?
20:35:10 <steve30> no thanks
20:35:14 <Halcyon> Okies
20:35:26 <Halcyon> Would you be interested in golf later?
20:35:53 <steve30> Its a bit wet outside to be playing golf
20:36:00 <Halcyon> On Steam :P
20:36:07 <steve30> I'll curl up on your lap and purr though :)
20:36:15 <Halcyon> Of course
23:09:28 <Halcyon> Ampera, you up?
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