[Elecraft] Long wire antennas MORE

[Don Wilhelm]

Dave,

All information I have seen says that the counterpoise needed for an 
EFHW is 0.05 wavelength - at 40 meters, that is about 3.5 feet.

If you make it longer than that, it becomes an offset center fed 
antenna, longer than a halfwave, in other words, it is a random length 
wire.  Both the half wavelength wire and the counterpoise wire will radiate.

73,
Don W3FPR

On 1/12/2018 7:43 PM, David Gilbert wrote:
> Well, since you brought up EFHW there is a relevant comment I've wanted 
> to make for a while.
> 
> An EFHW with a counterpoise wire (which everyone seems to claim is 
> important to have) is basically just an extreme version of an off-center 
> fed dipole.  A half wave dipole has its lowest impedance at the center, 
> where the current is high and the voltage is low.  As you move out away 
> from the center the current decreases and the voltage increases, which 
> is equivalent to saying that the impedance increases.  As you get to the 
> end of the wire the current obviously goes to near zero except for 
> capacitive currents while the voltage goes very high ... meaning high 
> impedance.  The "counterpoise" for an EFHW is merely an extension that 
> puts the feedpoint back toward the center where the impedance isn't 
> quite as high.  And as with any dipole, it isn't critical how that 
> "counterpoise" is physically arrayed because the current there is small 
> so it doesn't affect the pattern much ... just as is the case with a 
> dipole with drooping ends.
> 
> I think if everyone viewed EFHW antennas as off-center-fed dipoles there 
> would be a lot less confusion about how they work.