I'm afraid someone already got a patent on electrostatic discharge.
I'm afraid someone already got a patent on electrostatic discharge.
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... "If it doesn\'t fit, use a bigger hammer!" --------------------------------------------------------------
John Larkin a écrit :
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Probably. Lots of people don't understand this and I've seen this kind of mistake (opened shield) recommended in lots of highly regarded EMC books.
But that's really nice for us. (Joerg?)
-- Thanks, Fred.
Oh yeah? You young punks have it easy. Back in my time, we didn't have plastic chairs. If we wanted to make sparks, we had to rub two cats together.
-- Paul Hovnanian paul@hovnanian.com ---------------------------------------------------------------------- Have gnu, will travel.
only if you bolted the camera to your head...
At the receive (instrument) end, the ungrounded end of the coax shield becomes the hot side of a resonant "vertical" antenna. Any voltage there becomes 100% common-mode signal on the inner twisted pair.
What's wrong with a little current in the shield? The signal pair isn't affected. But volts, or tens of volts, of common-mode RF can be nasty.
John
Just hit the top of your head with your fist. You'll see the typically underdamped transient response of your visual tracking system.
John
When I was a kid, my brother built a Heathkit TOOB amp; in the low level circuits, they only ever grounded one end of the shields.
Cheers! Rich
Yeah! But shhht, don't spill the beans here, at least not until I am retired :-))
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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No, which is precisely the reason to ground only one end of the shield.
Cheers! Rich
Inside a steel chassis pan, it wouldn't matter. But then Heathkit was hardly an authority on signal management.
John
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It could become really, really nasty if the cable length happens to be close to 1/4, 3/4 and so on wavelength of the offending RF signal. If the shield current is of concern it can be broken by a wee ferrite.
Probably the litmus test for RF stuff like this is when people schlepp it to Otis Street and see if it can survive Sutro Tower.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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Now wait a minute, they engineered darn good stuff. The old HW100/101 transceivers were among the best ever made back in the tube days. Still got one. No noises or buzzes whatsoever and its performance in the vicinity of strong signals is stellar. The only not so good thing was the two rubber pulleys because they cooked out too fast, but you could keep a stash of them in the drawer.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
I think I'll retired after you, but this kind of misconception is sufficiently widely spread that we don't have to worry :-)
-- Thanks, Fred.
They had more volts in them as well
-- Dirk http://www.transcendence.me.uk/ - Transcendence UK http://www.theconsensus.org/ - A UK political party http://www.onetribe.me.uk/wordpress/?cat=5 - Our podcasts on weird stuff
Oh, I am not worried at all :-)
But I am concerned about what happens when guys like you and I are in their 90's, the hands are shaky, the mind ain't what it used to be and the senior living place doesn't allow a Tektronix mainframe in the rooms. The next generation doesn't have anough analog engineers.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Yup. Once people get fixated on "ground loops" they are forever lost to reason.
Ditto high-speed "return currents."
John
Bad focus but shows the concept, when I was a teenager I made almost everything in wood, nicely polished, several layers of laquer, some more polishing:
I usually spent a lot more time on the enclosures than on the electronics but the stuff is still working.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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Or a nice wideband ESD spark. Then the receive-end differential signal might see a kilovolt p-p common-mode ring.
If
Right. That's easy to add as needed.
It's terrible here. Scope traces are gross fuzz, and all sorts of opamp front-ends like to rectify stuff.
You should see the spectrum of a 10" clip lead.
We did do a useful simulation of a system that has a superconductive magnet/front end on one side of a room and some ADCs on the other side. We convinced ourselves that we need to go differential.
John
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Toob amps didn't rectify RF as well as silicon does.
John
[snip]
Won't matter. We'll all be deep into communal despair :-(
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Think things are bad now? Wait until Obama "takes care" of you.
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