Originally Posted by

On Jan 10, 6:01*am, tzitzikas
wrote:
hi.
i have a transmitter about 150 watt (output an 813 tube 1400vdc) at
1431khz (salonika greece) and the antenna that i'm using is an inverted
L antenna (with a less than 5l/16 length ,about 20m vertical segment and
40m horizontal segment). the coupler that i'm using now is l-type . athttp://www.geocities.com/tzitzikas_ee/antenna.gifyou can see a
schematic of my coupler.
i would like to improve the efficiency of my antenna.
i would like to ask you which inverted L lenght is better for stronger
local signals:
1/2, 3/8, 5/16, 5/8 or 1/2 wavelenght? thanks

--
tzitzikas

The only way to improve efficiency is to improve the ground
radial system.
With the exception of current distribution possibly effecting
efficiency, which again actually leads back to ground loss
around the base of the antenna, changing the length of the
radiator only effects the pattern.
And being you are transmitting to locals using ground or
space wave, you want the polarization to be as purely vertical
as possible. So unless you can erect the longer length radiators
as verticals, using the longer lengths would probably hurt you
rather than help. You will have more radiation from the
horizontal section of the radiator, which is not what you want.
As far as the radiator, one of the best ones to use has already
been mentioned. The "T" vertical. You want to use a balanced
top hat, or wires, so that the radiation from the horizontal sections
cancels out. That will leave you with a mostly vertical polarization.
So it sounds like the me the best radiator is the longest vertical
wire you can erect, with a T horizontal section, not as an Inv L.
Once you do that, the only way to improve efficiency is to add
more ground radials.
The longer length radiators will only help your case if they are
fully vertical. A short vertical section with the rest horizontal is
going to hurt you, not help. Well, unless you are working NVIS..
But this is not the case operating a local MW station to other
locals.