Transmission lines Was: UNIBUS extension card/cable sets

Toby Thain toby at
Thu Jun 25 11:14:16 CDT 2015

On 2015-06-25 12:02 PM, Noel Chiappa wrote:
>      > 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! :-)

For the YouTube generation - there's Dr John Shive's 1959 video:

Note, there's an intro of 1 min 20 seconds.


> 	Noel

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