Topband: INV L Directionality

[George (K8GG) & Marijke Guerin]

Jerry, K3BZ wrote:

----- Original Message ----- 
From: "Jerry Keller (K3BZ)" <k3bz at arrl.net>
To: "(Reflector) TopBand" <topband at contesting.com>
Sent: Friday, August 31, 2007 9:07 AM
Subject: Topband: INV L Directionality


> Is an inverted L directional at all?  If so, is it directional off the 
> sides
> of the horizontal element?
> 73, Jerry K3BZ

Many on the Topband Reflector have modelled inverted-L antennas.  There is 
generally a 1 or 2 db vertically polarized gain away from the top loading 
wire.  If the toploading wire is long, i.e., more than 1/8 wl, then there is 
also a horizontal polarized sky wave.

This can be also seen in the models for the EWE antennas, where the "far 
end" is returned to the ground with a loading resistor.  The inverted-U then 
becomes highly directional away from the horizontal wire direction.

Relative to 165 and 185 foot long inverted-L's they approach 1/4 wl 
horizontally on top of the vertical wire, which sends a lot of energy nearly 
straight up, reducing the low angle energy.  One can build a 1/4 wl 
inverted-L and feed it with an UnUn or L-network or maybe go 7 feet (2 
meters) long and put a shunt capacitor to ground to raise the impedance to 
about 50 ohms.  (The extra wire is about 2 uHy of inductance as half of an 
L-network)

73        George    K8GG