Topband: [Topband] Inverted "L" vs." T"

[Rick Karlquist]

K4SAV wrote:
> W7RH wrote: Further with the T portion as top loading the feed point
> radiation resistance will be greater for a given vertical
> height. This when coupled with an excellent ground system of 1/4 wave
> radials will make the antenna substantially more efficient than other
> types of loading. (Less Loss)
>
> Why does NEC not confirm this statement?  An example: A T antenna and an
> L, both with the same ground loss, the same vertical section length
> (49.5 ft), and the same resonant frequency.  The T calculates as a
> feepoint impedance of 18.1 ohms at 1.81 MHz.  The L calculates as 20.2
> ohms at 1.81 MHz.  If you calculate the radiation resistance, the L will
> be 1.5 to 2 ohms higher.

The higher radiation resistance and lower ground loss of the inverted
L is illusory, because the additional radiation represents horizontallly
polarized waves, which tend to be inefficient for communications purposes
on 160 meters most of the time, especially at typical inverted L heights.

If you do an NEC model with a second reference vertical, say 5
wavelengths away, and look at the amount of vertical power received by
the second reference vertical, then you will see that the horizontal
section of the inverted L contributes nothing, whereas a T top actually
increases received signal.

Hope that clears up this persistent misconception.

Rick N6RK