On 10/11/22 10:47, John Larkin wrote:> "Avoid ground loops" makes no sense for fast stuff, and doesn't even > make sense for audio or thermocouples.Says the man who's obviously never operated an audio system in a hall where you can get >1VAC between the grounds of different outlets.
spread spectrum cheating
Started by ●November 3, 2022
Reply by ●November 9, 20222022-11-09
Reply by ●November 9, 20222022-11-09
On Wednesday, November 9, 2022 at 9:33:14 PM UTC-4, Clifford Heath wrote:> On 10/11/22 10:47, John Larkin wrote: > > "Avoid ground loops" makes no sense for fast stuff, and doesn't even > > make sense for audio or thermocouples. > Says the man who's obviously never operated an audio system in a hall > where you can get >1VAC between the grounds of different outlets.Even among engineers, few people understand grounding concepts. There are times when "every possible ground" is not a bad idea, like car starters. But in multi-rack electronics, it's best to have one ground to every cabinet, in a star topology. At least, that's what I've always read and it seems to work on the systems I've used. I've seen discussions of *which* end of a shield should be grounded, usually it's the driver end, unless it's bidirectional, of course. But using a shield to provide a chassis ground is clearly not a good idea. What's wrong with providing one really good ground? -- Rick C. + Get 1,000 miles of free Supercharging + Tesla referral code - https://ts.la/richard11209
Reply by ●November 9, 20222022-11-09
Clifford Heath <no_spam@please.net> wrote:> On 10/11/22 10:47, John Larkin wrote: >> "Avoid ground loops" makes no sense for fast stuff, and doesn't even >> make sense for audio or thermocouples. > > Says the man who's obviously never operated an audio system in a hall > where you can get >1VAC between the grounds of different outlets.Don't they make transformers for that situation? Of course, nowadays everything is probably WiFi. Look at the stage microphones used by Taylor Swift, Madonna, Rihanna and others. -- MRM
Reply by ●November 9, 20222022-11-09
On Wed, 9 Nov 2022 10:50:43 -0800 (PST), "John Miles, KE5FX" <jmiles@gmail.com> wrote:>On Wednesday, November 2, 2022 at 8:00:11 PM UTC-7, John Larkin wrote: >> We make a bunch of boxes that go into a semi fab tool. One measures an >> optical waveform and shoots it to a bigger box, over three twisted >> pairs (clock, data, data) using shielded RJ45 ethernet type stuff. >> > >Probably a dumb question, but those clock and data signals are source- >terminated to drive ~100 ohms, right? If you have standing waves >on the wire pairs, I can see them exciting the ungrounded shield at the >current points, making a very effective antenna. Radiation from the cable >could easily be 30 dB worse than expected. > >-- john, KE5FXBoth ends are terminated, so there should be no standing waves.
Reply by ●November 9, 20222022-11-09
On Thu, 10 Nov 2022 12:33:07 +1100, Clifford Heath <no_spam@please.net> wrote:>On 10/11/22 10:47, John Larkin wrote: >> "Avoid ground loops" makes no sense for fast stuff, and doesn't even >> make sense for audio or thermocouples. > >Says the man who's obviously never operated an audio system in a hall >where you can get >1VAC between the grounds of different outlets.Critical signals should be differential. And with audio, you can transformer isolate.
Reply by ●November 9, 20222022-11-09
On Thu, 10 Nov 2022 02:45:40 -0000 (UTC), Mike Monett VE3BTI <spamme@not.com> wrote:>Clifford Heath <no_spam@please.net> wrote: > >> On 10/11/22 10:47, John Larkin wrote: >>> "Avoid ground loops" makes no sense for fast stuff, and doesn't even >>> make sense for audio or thermocouples. >> >> Says the man who's obviously never operated an audio system in a hall >> where you can get >1VAC between the grounds of different outlets. > >Don't they make transformers for that situation? > >Of course, nowadays everything is probably WiFi. Look at the stage >microphones used by Taylor Swift, Madonna, Rihanna and others.RF doesn't have ground loops! Fiber doesn't either.
Reply by ●November 10, 20222022-11-10
On a sunny day (Thu, 10 Nov 2022 12:33:07 +1100) it happened Clifford Heath <no_spam@please.net> wrote in <1726152b585b226c$2$549519$5aa10cad@news.thecubenet.com>:>On 10/11/22 10:47, John Larkin wrote: >> "Avoid ground loops" makes no sense for fast stuff, and doesn't even >> make sense for audio or thermocouples. > >Says the man who's obviously never operated an audio system in a hall >where you can get >1VAC between the grounds of different outlets.Indeed, even here at home it is sometimss a problem.
Reply by ●November 10, 20222022-11-10
On a sunny day (Wed, 09 Nov 2022 12:41:42 -0800) it happened John Larkin <jlarkin@highland_atwork_technology.com> wrote in <ds3omhpt2tbe0fnr448i24vuqp3nr36hug@4ax.com>:>On Wed, 9 Nov 2022 11:11:06 -0800 (PST), Lasse Langwadt Christensen ><langwadt@fonz.dk> wrote: > >>torsdag den 3. november 2022 kl. 04.00.11 UTC+1 skrev John Larkin: >>> We make a bunch of boxes that go into a semi fab tool. One measures an >>> optical waveform and shoots it to a bigger box, over three twisted >>> pairs (clock, data, data) using shielded RJ45 ethernet type stuff. >>> >>> When we originally did it, they told us we were exempt from ROHS and >>> EMI standards, but now we aren't. ROHS is no big deal, but the little >>> box makes a continuous 62 MHz clock, differential at 5 volt swings, >>> and radiates too much. >>> >>> We can't lowpass filter the fundamental of course. We can't drop the >>> amplitude much. A common-mode balun might help some. >> >>if it is balanced why do you need such a massive swing? >> >> > >The original design, about 10 years ago, used a big swing and a >receive-end attenuator to give a lot of common-mode rejection against >ground loops. This system is spread over floors of a big expensive >building. > >We were exempt from EMI standards then.Go optical?
Reply by ●November 10, 20222022-11-10
On Wednesday, November 9, 2022 at 7:15:44 PM UTC-8, John Larkin wrote:> On Thu, 10 Nov 2022 12:33:07 +1100, Clifford Heath > <no_...@please.net> wrote: > > >On 10/11/22 10:47, John Larkin wrote: > >> "Avoid ground loops" makes no sense for fast stuff, and doesn't even > >> make sense for audio or thermocouples.> >Says the man who's obviously never operated an audio system in a hall > >where you can get >1VAC between the grounds of different outlets.> Critical signals should be differential. And with audio, you can > transformer isolate.Differential is good, but an audio transformer and ~100 ohm transmission line has to have inductance large compared to 100 ohms at 20 Hz; to get a factor of four, that comes to about 900 mH; it's not gonna be a small transformer if the wire resistance is to be kept low. SPDIF, and your choice of coax or fiber, is a better transmission choice than transformers.
Reply by ●November 10, 20222022-11-10
On Wednesday, November 9, 2022 at 11:17:04 PM UTC-4, John Larkin wrote:> On Thu, 10 Nov 2022 02:45:40 -0000 (UTC), Mike Monett VE3BTI > <spa...@not.com> wrote: > > >Clifford Heath <no_...@please.net> wrote: > > > >> On 10/11/22 10:47, John Larkin wrote: > >>> "Avoid ground loops" makes no sense for fast stuff, and doesn't even > >>> make sense for audio or thermocouples. > >> > >> Says the man who's obviously never operated an audio system in a hall > >> where you can get >1VAC between the grounds of different outlets. > > > >Don't they make transformers for that situation? > > > >Of course, nowadays everything is probably WiFi. Look at the stage > >microphones used by Taylor Swift, Madonna, Rihanna and others. > RF doesn't have ground loops! Fiber doesn't either.No, but shields connected at both ends along with other ground connections do. -- Rick C. -- Get 1,000 miles of free Supercharging -- Tesla referral code - https://ts.la/richard11209
