Tom,
Yes I agree that my example is very extreme and one that an amateur
operator would not intentionally create as a permanent antenna system.
I have some meetings with a couple old RF matching gurus next week. We
will have some fun digging through the article. If anything
enlightening surfaces, I will post it to the reflector.
Thanks,
Jay
Tom Rauch wrote:
>
> Jay,
>
> What Best forgot, and what you also neglect to mention, is
> amateur antennas with MODEST SWR VALUES work just fine with
> some mismatch even using regular coaxial cables.
>
> Loss is nowhere near the "match efficiency" or "reflected power"
> would indicate, IF the transmitter or receiver end is matched with a
> matching network.
>
> If the transmission line has low matched loss, it will also have less
> mismatched loss. That why open wire lines can be operated with
> extreme SWR and still have excellent efficiency.
>
> Best, despite openly flaunting his "experience and credentials",
> initially had that concept totally wrong! I'd respect him today if he
> had been able to utter the words "I made a mistake".
>
> With lines under 1/4 wl, minimum line loss can (and usually does)
> occur with an INTENTIONAL mismatch! That's because an
> overwhelming amount of line loss is due to conductor resistance
> and NOT dielectric losses (as many people seem to think).
>
> Air insulation in feedlines offers less loss mainly because
> impedance is higher for a given conductor size. There is less
> current and lower I^2 R losses because the line has higher
> impedance for a given conductor size, or the same impedance line
> uses a LARGER conductor.
>
> The change by matching at the load in TYPICAL installations when
> using feeders with very low loss is negligible, just as is the change
> when the line is short.
>
> There are some exception. Situations can add significant loss...
>
> 1.) Lines with significant initial matched loss
>
> 2.) Line where VAR power in the line becomes extremely high
> (current becomes extremely high in areas of the line).
>
> Your use of the plasma coupling as an example is about like telling
> us about losses when feeding an unloaded six foot mobile whip on
> 3.5 MHz with a tuner at the rig.
>
> When a person spews several pages of complex math based on an
> extreme examples (as Best did), or gives an example based on a
> SWR that would make most calculators overflow (as you did), it
> probably does more harm than good to the people who are trying to
> learn.
>
> The poor bloke trying to understand what it all means is left with a totally
> wrong impression.
>
> Bottom line is.... if feedline loss is fairly low in a matched condition
> a system can tolerate a fairly high SWR with NO noticeable
> change in performance on receive or transmit if a matching network
> is placed somewhere in the feedline system.
>
> Feeding a six meter dipole on 160 meters is more in line with your
> Plasma example. Feeding a dipole cut for 21MHz on 18 MHz is
> more in line with the real world.
>
> 73, Tom W8JI
> w8ji@contesting.com
>
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