[Towertalk] OCF Longwire with moveable feed point

[n4kg@juno.com]

On Mon, 22 Apr 2002 "Terry O'Neill" <cpa2000@yahoo.com> writes:
> 
> The Antenna Book (17th edition) suggests a 3.5 wl single wire 
> antenna has a take off angle of about 28 degrees. It does not 
> indicate that the TO angle is dependent on the height of the wire, 
> but I would guess it has to be at least 1/2 wl high to achieve the 
> indicated TO angle.
> 

TakeOff Angle is VERY much dependent on height of the antenna.
The Radiated Pattern over ground is computed by multiplying the
Free Space Pattern of the Antenna times the Ground Reflection
Coefficients which are a function of the height of the antenna in
Wavelengths.  

See pages 3-11 to 3-13 of the 17 th Edition of the ARRL Antenna
Book for those patterns for half wave (dipole) antennas broadside 
to the antenna, at 45 degrees to the wire, and off the ends of the wire.

To see the effects of height on a Long Wire Antenna,
you would need to model the antenna at different heights.
Compare those patterns with the free space patterns.

The NULLS in the Long Wire patterns are REAL.
To obtain 360 degree coverage requires multiple antennas
to fill in all the pattern NULLS.  I use a 20M dipole fed with
ladderline which only radiates broadside to the wire from
10 through 30 meters to fill in the pattern nulls of my 80M
dipoles when used on the high bands.  ALL of my WARC
Band DXing has been done using various dipoles for 20,
30, and 80M resulting in over 320 countries on each band.

Tom  N4KG



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