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An unusual Oscilloscope phenomenon

Discussion in 'Hobby Electronics' started by David L. Jones, Jun 25, 2009.

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  1. Check out a rather unusual phenomenon you can see on your oscilloscope in my
    latest blog (#14):
    http://www.alternatezone.com/eevblog/
    See if you can get it to happen on your scope!
    I'll offer a free subscription to my blog for the best screen shot posted
    :->

    Oh, and the probe doesn't have to be shorted either.

    Have fun.
    Dave.
     
  2. Got it immediately, because I once worked in lab that had cheap plastic
    chairs that generated 1cm sparks when you stood up!

    --
    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
     
  3. No. Where?

    Dave.
     
  4. Yep, an open Altronics box!
    Curiously though the contents were made in Australia and not China - how
    novel!

    Dave.
     
  5. TonyS

    TonyS Guest

    IIRC head signals mostly went via twisted pair. If they had a shield as well we
    would certainly not ground them on both sides.

    Tony
     
  6. Back in the old days, they used to generate 1/2" sparks.
     
  7. Dennis

    Dennis Guest

    Nasty stuff that Bakelite.
     
  8. amdx

    amdx Guest

    If you set the time base correctly and crunch down on a carrot
    you will see a complex waveform on the scope.
    Very difficult to store on a digital scope though. :)
    Mike
     
  9. Dennis

    Dennis Guest

    When I started out with a government run telco and some of the gear was
    still in nice wooden cases. Over the years I saw pallet loads of test gear
    consigned to scrap. Loads of bridges, wood cased multimeters and bakelite
    AVO meters. These things sell for quite a few dollars nowadays - aint
    hindsight nice!
     
  10. terryc

    terryc Guest

    Lunch pictures?
     
  11. Nico Coesel

    Nico Coesel Guest

    I'm afraid someone already got a patent on electrostatic discharge.
     
  12. Fred Bartoli

    Fred Bartoli Guest

    John Larkin a écrit :
    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?)
     
  13. Rich Grise

    Rich Grise Guest

    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
     
  14. Joerg

    Joerg Guest

    Yeah! But shhht, don't spill the beans here, at least not until I am
    retired :))
     
  15. Rich Grise

    Rich Grise Guest

    You *want* large amounts of high-frequency common-mode noise?
    [/QUOTE]
    No, which is precisely the reason to ground only one end of the shield.

    Cheers!
    Rich
     
  16. Joerg

    Joerg Guest

    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.
     
  17. Joerg

    Joerg Guest

    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.
     
  18. Fred Bartoli

    Fred Bartoli Guest

    Joerg a écrit :
    I think I'll retired after you, but this kind of misconception is
    sufficiently widely spread that we don't have to worry :)
     
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