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  • EEVblog #311 – Jim Williams Pulser Followup

    Posted on July 16th, 2012 EEVblog 11 comments

    Some follow-up measurements on the Jim Williams pulse generator circuit.
    With a special guest appearance by a rather expensive scope

    The Amperes T-Shirt is available HERE

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    11 responses to “EEVblog #311 – Jim Williams Pulser Followup” RSS icon

    • EEVBlog, Not sure if you got my message on twitter. I was wondering how much longer
      you’ll have that 13GHz scope. I built a small board with some fast CMOS logic inverters (forget exact part number) that can produce square waves rather than just pulses, and I found that the rise and fall times were <300ps when I had the opportunity to measure it on a scope like the one you've borrowed. If you'd like to have a play with that little square wave generator, I could send it to you. As I'm in Australia it should get there next day.

      Another interesting thing to do with those fast oscilloscopes is to stick about 2.5cm (1") of wire into the input connector (or preferably an adapter, don't want to damage the scope's connector!), then get a plastic bag and put a 5-10 coins in it, then jingle the bag of coins a metre or so from the little antenna wire. It is quite surprising how many volts can be induced in the little antenna just from the coins, it's pretty easy to get several volts, so start off far away or use an attenuator. I found out about that phenomenon here:
      http://emcesd.com/tt2004/tt090104.htm

      Chris

    • Excellent investigation Dave.

    • No ocilliscopes were actually harmed during the filming of this video.

    • It looks like you used coaxial adapters from “One Hung Low” – these cheap adapters can be a real problem in terms of maintaining constant impedance. For that matter, even high quality adapters are subject to problems.

      Where the lack of constant impedance will show up is in ripples as the direct and reflected waves combine in and out of phase. This could be why you see so many lumps in the pulse.

      It would be interesting to see if a BNC attenuator of high quality would smooth out some of the lumps.

      Inexpensive (Mini-Circuits) BNC attenuators are rated to 2 GHz, whilst their SMA and N versions are rated at 18 GHz or so.

      Jack

    • I see we got a preview of what Dave’s tearing down this tuesday!

    • I would really like to buy one or two of these pulse generators (built and tested). Is that possible. Seems like a really useful tool.

    • So when are we going to see a teardown of this scope? Dare you open the box? :o I’m sure Agilent will let you, just might want to get some insurance first… :)

    • I like your Blogs but sorry you stick the Attenuator with about a hundred of bnc adapters directly into the scopes connector :-P Please use a little Cableadapter even more so its a 150k $ scope as an Electrician it hurts when you see this :-)

      Greetings from Germany ;-)

    • HI Dave!

      I’ve seen this little flat bit in the rising edge at 7:00 min before, in my Signal Integrity class. The additional coax forms a transmission line of course, which is not terminated! :(
      So you have to wait the propagation delay of the t-line to have the full peak due to the reflexion at the end.
      I’ve modeled your case in LTSpice with the tline component and got a similar result.

      Greetings from Germany ;)

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