Cable impedance upper limit in Radcom Plus?
RSGB members may have seen the latest Radcom Plus e-magazine. In it there is an interesting article on transmission lines, but I am not sure I believe everything it says. The author says that the Heaviside Telegrapher's Equation does not tell the whole truth about transmission lines (true - it only applies in the low frequency approximation of EM, otherwise known as circuit theory) so there are other modes apart from the usually dominant TEM (true - but usually irrelevant until you get to very very high frequencies).
The contentious part is where he claims that no transmission line can have a higher characteristic impedance than free space (i.e. 377R), and that if you calculate a higher one assuming TEM then the other modes adjust it downwards to get below this limit. He claims that this explains anomalies seen in precision RF labs. He also says that this new theory explains the 'single wire' feeder.
If 377R is an upper limit then I would expect some anomalies to be seen with a 300R line, and some people claim to have used 450R open wire feeders. I am very sceptical about this particular claim, especially as he does not explain it but merely refers us to other publications - which may or may not say what he thinks they say.
What do others think?
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