Re: VSWR doesn't matter?

joseph2k wrote:
>> >> Do us a favor, compute the S-vectors for an incandescent lamp with a >> linear filament. >> Then follow though with the same for a transmitter, transmission line and >> a mismatched load. >> You will find that is the reflected S-vector that adds heat to the plate. > > By "us" I assume you mean "you". But sorry, what you're asking makes no > sense to me. Perhaps you can do this exercise and show what you mean. > > Roy Lewallen, W7EL

By us i mean all the competent engineers here, including Win, JT, JF, and many others. The list does not include the potty mouth prone misfits.

Somewhere in a this thread or a variant someone proposed that the power is somehow stored in the transmission line. That would result in an ever increasing stored energy; sooner or later the voltages and currents involved would destroy the conductors and insulators. (And promptly for transmitters above a few watts, with more that 1% mismatch.)

Well, standing waves (the SW in VSWR, voltage standing wave ratio) are interference patterens between the energy that is, indeed bouncing back and forth from end to end of the transmission line. That portion of the energy does, eventually, get dissipated is heat, instead of a useful signal from the antenna. This is why people want to minimize it, at least in transmitters. A low VSWR in a receive antenna/feedline just lets more useful signal get to the receiver, rather than being dissipated in the line as waste heat.

Antenna tuners compensate for that by adjusting the reactive impedance where the line meets the unit.

Admittedly, this is essentially from the 1963 Radio Amateurs' Handbook; maybe they've discovered some new form of science in the meantime, where standing waves don't dissipate any power, and now VSWR doesn't matter any more.

Thanks, Rich

Hope This Helps! Rich