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Test your eq
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Issue #226 May 2009
Robert Lacoste recently wrote about transmission lines and time-domain reflectometry (TDR) in Circuit Cellar issues 224 and 225. Let’s explore that topic a little further.
Problem 1—Suppose we use a step waveform (instead of a narrow pulse) to excite the transmission line circuit shown below. What sort of waveform would you expect to see at point A?
Problem 2—Can you reconcile your answer to the previous question with the waveform created by pulse excitation that Robert Lacoste discussed in Circuit Cellar 225?
Problem 3—Suppose you have a circuit that is capable of producing step waveforms with very fast rise times. How can you use a transmission line to convert the steps to narrow pulses?
Problem 4—Joe is a ham radio operator, and he likes to operate on the 6-m band (50 to 54 MHz). One day Bill is visiting Joe’s “shack,” and notices that Joe has a tee adapter on the transmitter’s antenna jack, and in addition to the cable to the antenna, there is a second piece of coax attached to the tee that doesn't seem to go anywhere. It appears to be about a foot long.
Bill asks Joe about it, who laughs and says, “Oh, that helps keep me legal!” What’s going on here?
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