yup. First job post uni was in a lab where we coupled up a signal generator to one end of a reel of coax, and used a twin beam scope to look at what came out the other end. Direct evidence for te speed of light! And pulse distortion. And reflection.
On a sunny day (Sat, 27 Jun 2020 16:38:07 +0100) it happened David Higton wrote in :
OP was discusing 74LS
Transitions are slower and it does not matter much if those are distorted. Measured that effect.
74LS inputs are not terminated.There is a lot of crap going around about RF. Here is a 1.something GHz board connected to raspi 1 GPIO:
scroll down for picture of the board backside. Where it is about 1 GHz (~ 30 cm wave length!!!) connections are short and direct, not wired. Wire length becomes important, 1/4 wavelength wires can do funny things. For the rest it is all simple.
Some interfaces for example between VCO an mixer and QAM modulator chip are 50 Ohm.
GPIO edges are FAST, yet the flat cable causes no problems and is in no way 'terminated'.
Aha. At last, someone else who understands transmission lines.
David
Yep I've seen the same, a so called professional wireman formed the wirewrap wires into neatly tied together bundles for address, data etc. Didn't work, and it was only running at about 1MHz too!
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