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Scope for UWB

Discussion in 'Electronic Design' started by oopere, Mar 29, 2007.

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  1. oopere

    oopere Guest

    We are in the process of acquiring a fast (12GHz) scope for testing
    impulsive UWB systems. We are considering the agilent DSO 81204 and
    the tektronix DSA 7124. Can anybody share his/her experience on any of

    I have been using tek scopes for a long time and think they are
    excellent. Almost no experience with agilent scopes excepting a mixed
    signal scope. However, in a demo I saw, a tektronix DSA 70804 seemed
    not to work as nicelly as could be expected: visible distortion in a
    1GHz sinusoidal signal, plus some non-intuitive zooming after a single
    shot capture. Seems there are different A/D techniques in both scopes.
    Comments are welcome!


  2. Phil Hobbs

    Phil Hobbs Guest

    I recently bought a refurb 7 GHz, 20 GS/s Tek scope (I forget the model
    number, they're all Wintel PCs with data acq hardware nowadays.) I
    bought the old one because the new one had something like 8% overshoot
    on the step response. (No, this is not Gibbs effect due to brick-wall
    filtering. It's due to a crappy vertical amplifier.)

    The new one was an early production sample, and I really leaned on the
    rep about maybe it got fixed, I don't know. A scope with edge
    artifacts like that isn't too useful, even if you _can_ play Halo on it.
    The Agilent folks seems to be going through one of those occasional
    periods in which they discover how to make scopes. They will probably
    forget again soon--the HP/Agilent track record in oscilloscopes is
    mixed, to put it kindly. I'll never forget the joy I felt about 18
    years ago in finding a _digital_ HP scope on the corporate surplus list
    for free. When it arrived, I discovered that I had to drill down three
    menu levels to set the vertical gain. It went right back on the surplus

    One thing that Agilent continually gets wrong is that they refuse to
    show you the actual measurement data. The trace on the screen has been
    massaged, compensated, filtered, and totally pimped by the time you see
    it. For my money, that's as bad as the ugly Tek impulse response.

    To the scope makers of the world: Just show me the measured data and let
    me interpret it myself.


    Phil Hobbs
  3. oopere

    oopere Guest

    Thanks for your inputs. Now I got to see an Agilent scope working with
    the same sinusoidal input signal. It really seems that there is less
    distortion. Agilent folks says this is due to very good matched A/D
    converters (at these speeds it seems the only choice is to interleave
    several A/D converters: Agilent interleaves 2 and Tek 5).
    However, your comment saying that Agilent refuses to show actual data
    has triggered an alarm: it could be that agilent's scope is cheating
    (i.e. filtering), because there was really a huge difference in the
    trace appearence for a simple sinusoid. In the Tek scope, it really
    seemed that some samples were either taken at the wrong time or there
    was a huge uncertainty in the quantization.

  4. Ian

    Ian Guest

    There's no way to cheat - the next signal you look at might be a
    completely different waveform. It is just easier to see the effects
    on a sine wave. You can see the effects on a square wave readily
    in the frequency domain.

    There's an article in the Agilent Measurement Journal about some
    of what they did at:

    (Agilent employee)
  5. Phil Hobbs

    Phil Hobbs Guest

    It isn't strictly true that there's no way to cheat--except on a
    single-shot measurement. Repetitive sine waves are easy.


    Phil Hobbs
  6. Ian

    Ian Guest

    Averaging on repetitive waveforms acts to smooth out noise.
    Systematic errors in the timing of the interleaved A/D's can't
    be fudged like that, you have to find a way to fix the problem.
    The article also says specifically that the sine wave plots were
    taken as a single-shot measurement.

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