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 these?
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!
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 it...so 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 list.
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.
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.
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:
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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