ars.w5omr at gmail.com
Sun Dec 31 10:38:24 EST 2006
Jack Schmidling wrote:
> Ed Sieb wrote:
>> You're missimg nothing, Jack.
>> There is no issue, really. Hooking up 50 ohm coax to a 75 ohm anteena
>> provides an SWR of 1.5:1, which is not excessive.
> From a student's point of view, most of the discussions on the subject
> start out with titles such as the importance of matching antenna to
> feed line. A 50% error or 25% deviation does not seem trivial.
> But from a practical standpoint, as 75 ohm coax is readily available,
> wouldn't it be better to use that?
Electronics is sometimes called "the exacting science of
approximation". Sometimes when you're building a circuit, your
calculatoins require (arbitrarily) a 432,354 ohm resistor (for
example). Resistor makers don't -make- a 432,354 ohm resistor. You
could get by with a 427,000 ohm resistor, or even a 470k ohm resistor,
and makde adjustments as necessary if it's *that* critical in your circuit.
The Exacting Science of Approximation.
We would -all- love to have things work in the REAL world, as well as
they do, theoretically, or on paper. Practical experience says that
nothing is ever perfect, so we get as close as we can, and then don't
worry about it.
If you're open-minded enough to listen to a suggestion, in order to feed
an antenna, consider using 450 ohm ladder line, or some open-wire
feedline, instead. The Velocity factor of wire is immensely faster than
coax, and therefore not nearly as lossy.
73 = Best Regard/*S*/
Happy New Year, ya'll!
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