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

[K4SAV]

Please disregard message below - sent to the wrong reflector - Jerry

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.
>
> Note: If you do these calculations with a Mininec ground, you will get 
> in incorrect answer because there will be a low horizontal wire over a 
> Mininec ground.  That always produces an impedance that is too low and 
> a gain that is too high.  You have to use a real ground and simulate 
> the radials, or do the calculations in free space.
>
> Jerry, K4SAV
>