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In Reply to: RE: Digital coax cable length posted by Peter C on July 17, 2017 at 11:20:22
" I don't see how it's true."
As you may see from the link this effect in co-axial cables has been known about since the late 1940s. There is lots of information online if you care to search.
Most calculations regarding SP/Dif connections conclude that 1.5 metres is the optimum length for attenuating the first reflection sufficiently.
Follow Ups:
I can't access the text because I'm not an IET member. I'm afraid that if I pay the $20 for the article, I may not understand much of it if it gets highly technical. Can you share the article, or do you think someone with a non EE background would get much from it if purchased?
Edits: 07/19/17
It will indeed be highly technical but you really don't need to know the details of the scientific research to buy a cable.
All you need is to read the precis contined in the link. This says that this is a paper published by the Insitute of Electrical Engineers ( note copyright notice) in 1952 and is based upon research undertaken from 1945 and 1948. It concerns reflections in a coaxial cable due to impedance irregularities. More particularly it is about differing methods for measuring it. If the effect did not exist then there could be no examination of measurement procedures.
Unless you believe that the IEE would be involved with a bogus paper and you have the technical wherewithal to effectively peer review the paper if you want to dispute it, all that you need to take on board is that the effect exists and has been recognised over a long history by major institutions. Therefore no one is fooling you by claiming that co-axial cables have signal reflections caused by impedance changes.
I would add that reflection of energy caused by a change in impedance is also well known in mechanical science.
Of course as the signal is reflected back along the cable the cable's electrical properties , particularly resistance, will mean that it is attenuated, hence the preferable length(s).
If you want to know more in layman's terms then Google is your friend. Like this kind of thing:
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