RE: NEC-LIST: QUESTION

Don:

As others have noted, the difference is real, and some of the reasons have
been given. In a real setup, you have to include the effects of the feed
line. It can go vertically (i.e., orthogonally) up to the horizontal dipole
and be brought away along the ground at right angles to to horizontal
elements. For a vertical dipole, the feed can either be that for a sleeve
dipole, and drop vertically down to the ground and away at right angles
along the ground, or it can be brought out horizontally from the feed at
the height of the feed for some distance and then away.

I have measured these feedline effects with both the SRI XELEDOP airborne
pattern measurement system and with the sounder technique I developed for
measuring the gain toward the zenith with a pulse-type ionospheric sounder
(see July 1973 Trans. AP).

The XELEDOP measurements of horizontal and vertical half-wave resonant
center fed dipoles were calibrated for absolute gain using a method I
developed, and later verified with NEC. The horizontal dipole puts out
more, but the radiation off the end of that dipole is "vertically
polarized."
When the horizontal HF dipole is very low to the ground (e.g., 2 feet),
the predominant radiation is the vertically polarized radiation off the end
and not the broadside radiation shown in text books for the dipole pattern.
This has been a misleading figure for many people.

Hope this helps.

Regards,

George Hagn

Original Message:
-----------------
From: Don Belcher dbelcher_at_wherenet.com
Date: Fri, 14 Feb 2003 08:37:21 -0500
To: nec-list_at_gweep.ca
Subject: NEC-LIST: QUESTION

Hello,
I am a fairly new user so this is probably a dumb question but I have been
comparing simple half-wave dipoles over typical earth, oriented vertically
and
horizontally. The patterns look as you would expect however if one overlays
the patterns, it sure looks like the horizontal is radiating a lot more
integrated power than the vertical (meaning it looks like the overall
radiation efficiency of the antenna/earth "system" is higher with the
horizontal). Of course the overlays are at the broadside azimuth for the
horizontal....

Just for grins, I am using a 21 MHz half-wave dipole about 20 feet high at
the
feed point.

Is there some factor of 2 or something similar that I am missing or is it
all
pattern effects and fooling me bacause I am looking at the horizontal's best
azimuth?

thanks
Don
dbelcher_at_wherenet.com

--
The NEC-List mailing list <nec-list_at_gweep.ca>
http://www.gweep.ca/mailman/listinfo.cgi/nec-list
--------------------------------------------------------------------
mail2web - Check your email from the web at
http://mail2web.com/ .
-- 
The NEC-List mailing list <nec-list_at_gweep.ca>
http://www.gweep.ca/mailman/listinfo.cgi/nec-list