Tag Archives: coax

Guess the cable length to win stickers!

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!