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Is this oscilloscope working nornally?

Discussion in 'Electronic Basics' started by Ricky Spartacus, Oct 17, 2003.

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  1. I`m new to oscilloscopes. Do all scope built the same when trying to
    see a digital signal? If you look at these scopes at this website
    below, you`ll find that the square waves on some scopes look normal
    but others just a dash lines. Normal being that we see a rise
    (vertical) line and a horizontal line when probing digital signals.

    If you look at model 5020 you`ll see block of square wave but on 5020G
    just dash lines. Is model 5020G scope not working properly? If not why
    is it doing this?
  2. Baphomet

    Baphomet Guest

    Normally, the criteria to see rise times is a good high frequency response.
    I think that for optimal reproduction, the frequency response x the risetime
    = .35 . I suspect that the problem you are seeing is more one of sloppy
    photography than anything else because several of the higher frequency
    scopes don't show the risetime whereas several of the lower frequency scopes
    do. The horizontal or flat portion of the waveform is more indicative of a
    good low frequency response, and I believe all of the scopes shown go down
    to D.C.
  3. CFoley1064

    CFoley1064 Guest

    If you look at model 5020 you`ll see block of square wave but on 5020G
    Hi, Ricky. It's normal. You need very fast vertical deflection compared to
    horizontal on digital signals. For analog scopes, you adjust the intensity of
    the trace so it's comfortable. You can get better visualization of the rise
    and fall, but you have to bump up intensity to the point that the slower,
    "flat" parts are too bright and start to fuzz. Generally a tech will keep the
    intensity turned down as low as is comfortable, because you want to avoid
    phosphor "burn-in", you can get crisper lines, and jacking up the brightness
    also puts more stress on the scope.

    If you're interested in looking carefully at the digital signal's rise or fall,
    you set the scope to trigger on + (rise) or - (fall), then expand the time base
    to look closely. If you're just looking at digital signals, though, usually
    you just assume it's a clean transistion unless you have reason to believe
    otherwise. (It's also possible, since the 5020G has a built-in function
    generator, they're trying to indirectly spin how clean the function generator
    digital output is???)

    I've owned a Gold Star scope similar to the 5020C for about 15 years
    (out-of-town field service, needed an inexpensive low-end scope in a pinch),
    and have _never_ had a problem with it. If you're looking for a low-end scope
    to start out with, and you're on a limited budget but still want to buy new,
    it's not a bad choice.

    Good luck.
  4. I'm wondering what kind of signal the top trace on the first scope is, Ive
    never seen anything like that before?
  5. I think it might be a video "stairstep" signal, bit IIRC the standard
    stairstep goes black to white, while that one is white to black. (but
    it's been over 20 years since I worked in a TV studio)
  6. Dan Dunphy

    Dan Dunphy Guest

    On dual channel, single beam scopes, there are 2 ways to get dual
    trace. Alternate, and chop.
    Alternate mode switches channel data on every sweep, so chanel 1 wil
    be on every other sweep, with channel 2 in between. This is effective
    on all but fairly slow sweep speeds, in where there is not enough
    persistance to show both channels.
    For this, you use chop, where the channel info switched back and forth
    several to many times during a single sweep. It the chop speed is near
    your sweep frequency, or a multiple of it, you will see a dashed
    lines, which I think is what you are describing, and sometimes they
    will walk across the screen, depending on the chop frequency relation
    to the sweep frequency.
    The pictures were too small to tell, in the link below.
    If you can put your hands on the scope, simply switch modes and you
    can determine what is going on.

    lineOn 17 Oct 2003 02:00:50 -0700,
    Colorado Springs, CO
    My advice may be worth what you paid for it.
  7. <snip>

    Welcome to the world of analog video. That signal appears to be either
    SMPTE color bars with subcarrier filtered off, or the 'Y' channel of
    (Y, R-Y,B-Y) color bars. It is being displayed at horizontal line
    rate. The time from sync pulse to sync pulse (the most negative
    portion of that signal) should be 63.555555.... microseconds.

  8. Baphomet

    Baphomet Guest

    It looks like it's a dual channel two trace scope which I take to mean four
    traces. It's really almost impossible (at least for me) to tell what they
    are but the bottom looks like a quasi-square wave (it could even be in
    chopped mode running at a high sweep speed looking like a square wave), and
    the others might be a sawtooth, and a pulse. It's almost definitely not one
    unique waveform.
  9. Baphomet

    Baphomet Guest

    Congratulations -

    You have come up with the first Rorshach Test for electronics :)
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