kj7gs babbled,
"Is an antenna's radiation resistance the same thing as its feedpoint impedance?"
No!
"it's the equivalent resistance that would be read if a resistor were put in place of the antenna"........
No, it's the resistance that, if inserted in place of an antenna, would consume the same amount of power that is radiated by the antenna.
"If so, then my next question"....
then you simply assume that they're the same. if you already think you know the answer then why ask the question? they are not the same. so premise for next 2 questions is invalid.
you have the answer to your first question. the fact that you didn't understand the answer doesn't make the properties of the two any more alike.
are you looking for someone to agree with you or argue with you?
"Isn't this the same as its complex impedance?"........
how can a pure resistance (measured in ohms) consuming the same amount of power radiated by an antenna be the same as a "complex impedance" (ohms, jXl and jXc) consisting of not only resistance, but also unknown values of capacitive and inductive reactance as well? how "different" is that?
and if we're going to discuss "spherical geometry" then you should know right off the bat that this doesn't have anything to do with your inability to understand the answer to your first question. the basis for spherical geometry as it pertains to antennas is the "isotropic source reference", a reference that only exists in theory and probably always will since it deals with the example of an antenna in the shape of a geometrically perfect sphere being used as a reference for determining the gain of other antennas. being so, we can never actually connect a feedline to the center of the sphere without disturbing the surface and in essence destroying the surface geometry of said sphere, so it remains a reference in theory, albeit an important one becuase it helps us define the ability of an antenna to produce gain, which put simply is the ability of a given antenna design to eliminate signal radiation in wasted angles and directions and concentrate radiation at angles and in directions useful for communications purposes. since the isotropic source radiates signal equally well in all directions it is the sensible reference for determining the gain of a particular design.
you should spend more time understanding the meaning of the terms used in the definitions and the concepts therein and then the "difference" would be a little more obvious.
"So how does a properly mounted quarter-wave whip exhibit 50 ohms without any matching network applied?"
by properly mounting it....when you mount it in the center of the vehicle on the roof. (standard passenger vehicle) since this location is central to the bulk of the vehicle and usually at the highest point, the body metals gradual "lowering" as we move away from the base of the antenna in most or all directions closely simulates the "drooping radials" of a ground plane antenna in that it raises the input impedance typically seen at the feedpoint from the typical 32 - 36 ohms to the required 50 ohms....
so....one more time.
impedance is the total passive opposition offered to the flow of electric current. (opposition to current flow)
radiation resistance is the value of resistance that when substituted for the antenna will consume all the power that is radiated by the antenna. (total absorbtion of all power at the load)
yes, those are different.
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