No, end fed halfwaves are not dipoles. They are monopoles. Take a look at the ARRL antenna book, LaPort, Johnson or any of the classic antenna books. There is a reason why all the AM broadcast Stations with halfwave end fed antennas have radial systems that consist of 120 radials that are 0.4 wavelengths long. Look at the licenses for KRLD, WIP etc. they can be found on fccinfo.com. I don't think KRLD would have spent over 200,000$ replacing their ground system If end fed half wave antennas were dipoles and did not need a radial system to be efficient radiators. The best way to picture an antenna (ARRL Antenna book) is as a capacitor with displacement current flowing between the plates. With a dipole each of the plates is a antenna element. With a monopole, one plate is the radiator and the other plate is ground. Since even good ground is a poor conductor, a large resistor has been inserted in the circuit. The radial system acts to reduce that loss resistance and increase the power radiated. Ray W8LYJ
Sent from my iPad > On Feb 11, 2017, at 16:46, Don Wilhelm <[email protected]> wrote: > > Ray, > > I think that is 'stretching' the facts a bit. > A halfwave dipole is a halfwave dipole whether fed at the center or at an end > or somewhere in between. > The radiation pattern and efficiency is the same. > The problem is that an end fed resonant dipole does need a little bit of a > counterpoise (0.05 wavelength) in order to be able to feed it properly. > > 73, > Don W3FPR > >> On 2/11/2017 4:07 PM, Gmail wrote: >> As was said previously, all end fed antennas are monopoles with >> displacement current flowing from the antenna element to earth. Unlike >> dipoles where the displacement currents flow from element to element. >> So without an adequate radial system to reduce the ground loss all end Feds >> regardless of length are only about 10% efficient. >> There are good reasons why 45 years ago when coax became readily available >> we switched from endfed monopoles to dipoles. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
