Transmission lines Was: UNIBUS extension card/cable sets
jnc at mercury.lcs.mit.edu
Thu Jun 25 11:02:53 CDT 2015
> From: John Wilson
> I chose the digital version of EE as my major precisely because I knew
> I'd flunk Fields and Waves. Transmission lines are black magic as far
> as I'm concerned!
I too have a hard time with analog in general, but transmission lines I seem
to be OK with.
The way I think about them is to model them as pipes, and the signal as a
sound (single pulse) sent down the pipe. Proper termination is like a piece
of cotton at the end of the pipe, it sucks up the sound and you don't get a
reflection. If you just cap off the end of the pipe (i.e. no termination),
the sound bounces, and you get an echo.
So if you have a small un-terminated branch, part of the pulse bounces off
the end, and comes back out, and then propogates both ways, so the original
pulse gets a messy trailer tacked on the back of it. Etc, etc.
I dunno how accurate this model of mine is, but it seems to work OK! :-)
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