Re: Antennas
Posted by
KEN-3 on
Dec 10, 2011; 9:07pm
URL: http://elecraft.85.s1.nabble.com/Antennas-tp7082240p7082320.html
A center fed half wave dipole is only 75 ohms in free space (I guess the ISS qualifies) or at a few specific heights (approximately .23, .46 and .74 wavelengths above ground). At other heights, it varies from as low as 45 ohms (over real ground) to as high as 100 ohms.
That's why I specifically said "at the PROPER HEIGHT is still a 50 ohm feed".
My statement wasn't really a broad statement, was it? It was pretty specific.
I have been reading the Handbook and the Antenna Book since the 10th edition came out in 1964.
Ken WA8JXM
> I get my elecraft mail in journal form so my response is delayed. I had to mention that people who make broad statements about feed lines and antennas should check the antenna book and handbook before producing the wrong information.
>
> Here is an example:
>
> "The impedance of the feed line does not change the impedance of the antenna. A half wave length dipole at the proper height is still a 50 ohm feed regardless of whether it's fed with 50ohm line or 600 ohm line."
>
> Last time I checked a dipole (single wire 1/2 wavelength center fed) is 75 ohms. The part of the statement about impedance of the feed line is correct but with swr on the feedline the apparent impedance can can different
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