[TowerTalk] Re: Can takeoff angle be too low?

Pete Smith n4zr@contesting.com
Thu, 21 Dec 2000 15:38:14 -0500


At 01:12 PM 12/21/00 -0600, N4KG wrote:
>My interpretation of the VERY HIGH (>5 WL) antenna
>observation that there are NO observable nulls is as 
>follows:
>
>Since the peaks occur at approximately 5 degree intervals
>and the earth is not perfectly flat, reflections from minor
>slopes (1 to 3 degrees) in the foreground tend to "fill in"
>the nulls.  At lower heights, these minor slopes may move
>the upper or lower edge of a lobe 1 or 2 degrees, but that
>is of little consequence when the lobes are >8 degrees wide.
>This is only a guess.  Any other theories? 

It also seems likely to me that there is considerable slewing and smearing
that results from the passage through the ionosphere -- After all, the
mechanisms at work are a combination of refraction and reflection, both
imperfect, plus probably some other things that are seen empirically but
not understood on the molecular level.  

If you haven't already done so, Tom, you might find it intriguing to look
at the field strength maps that are produced by the VOAAREA program in the
VOACAP suite.  The patterns require a lot of thought to relate to the
antennas on either end of the path!  It is very hard/practically impossible
to see the regular variations in signal strength up- and down-path that you
might expect with antennas with well-defined vertical lobes.

73, Pete N4ZR

Contesting is ... Extreme Radio

The World Contest Station Database 
is back up and running at
http://www.qsl.net/n4zr 



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