Electronics

Guess the cable length to win stickers!

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Part 1:

An HP 3312A function generator is connected to an Agilent DSO1014A oscilloscope via a length of coaxial cable.  The function generator is set to generate a square wave of frequency 1MHz.

Based on the screen capture below, what is the length of the coax cable?

Unterminated Cable
Agilent DSO1014A Screen Capture

The first person to post a comment with:

  • the correct answer within ±10% of the actual measured length
  • a general explanation of how you arrived at this number (show your work!)

gets some free stickers as a reward!

Hints:

    1. The coax is labeled RG58A/U.
    2. The input impedance of the DSO1014A is nominally 1MΩ + 18pF.
    3. In case it’s not obvious, the scope photo shows two curves.  The bottom curve is a zoomed in version of the top one, showing the rising edge only.  This means that the time per division for the bottom curve is different from the top curve.  Thankfully, Agilent shows the time/div at the bottom of each so you don’t have to guess!

      Part 2 (Extra Credit):

      The function generator claims to have an output impedance of 50Ω.  Is this true?  Can you make a rough estimate of what the actual output impedance is, based on the screen capture above?

      Note: Random guessing is not allowed.  Please show that you made some honest attempt to solve the problem, even if it is by unconventional means!

      Electronics

      Tools!

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      Peter Edwards of Casper Electronics shared a picture of his workbench today via Make.

      With the exception of the audio recorder and circuit bending tools, pretty much every piece of equipment on that bench can be found on mine as well.  I even have the same yellow bins!

      There’s a great writeup on his site describing each numbered tool in the photo.  If you started from scratch and bought all of the items on his list, you would have a great instant electronics workshop.

      Books and Resources

      Coombs: Printed Circuits Handbook

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      Printed Circuits Handbook

      If The Art of Electronics is the bible of electronic circuit design, then the Printed Circuits Handbook is almost certainly the bible of printed circuit board (PCB) technology.

      I say this because even if you disregard the volumes of useful information inside (much of which I have never seen elsewhere online or in print), this book deserves to win ‘bible’ status thanks to its 1000 pages and phonebook-quality heft!

      All joking aside, this book is a great resource for anyone is serious about making good PCBs.  I have worked with PCBs as a design engineer for several years now, and I learned something about printed circuit boards within minutes of opening the cover.  Hours later, I was still flipping pages.

      How could I walk away from a book that contains in depth discussions of topics like the difference between water soluble and no-clean flux and how to clean the leftover residue from each?  Ever wondered what the myriad of surface finish options your PCB vendor offers you really mean?  This book will explain the difference between HASL and ENIG, and why you shouldn’t blindly check the box that says “lead-free” without considering the consequences on your assembly process.

      This is the kind of stuff they don’t teach you in school, and as a design engineer I have received only glimpses of in the industry.

      Some of the highlights of this book for me are:

      • The most thorough discussion of PCB manufacturing that I have ever seen (almost 300 pages!).  Want to know how the PCB you just got was made?  One layer or sixteen layers, it’s all in here.
      • Lots of information about custom laminates, high density interconnect techniques, microvias, blind/buried vias, plating and surface finishes, solder masks, conformal coating, etc.
      • Several charts of current handling ability of PCB traces, planes, and vias.
      • A chapter on thermal design of PCBs.
      • Lots of information about soldering techniques.  Ever wondered how soldering works and what flux really does?  It’s in here too.
      • Seven (!) chapters on design, manufacturing, and test of flex circuits.

      Be forewarned that the technical level of this book is fairly high.  It is clearly targeted towards people working in the PCB industry, but most engineers and even serious hobbyists would probably get something out of it.  That said, this is definitely not a book for beginners!

      (And to the other design engineers out there: Want to one-up the manufacturing and reliability guys in the break room?  Read this book!  :-))

      Printed Circuits Handbook (McGraw Hill Handbooks)

      Join the resistance.