[Elecraft] EFHW

[Gmail]

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 <donwilh at embarqmail.com> 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.