[TowerTalk] Shadowing

[Pete Smith]

OK, guys ... I had no idea when I mentioned a pair of Force 12 antennas as
examples of potential shadowing that this would evolve into a wrangle over
those particular antennas. Let's try to get general again.

Just for fun, I modeled a simple test case.  I took the 3-el NBS yagi model
that ships with EZNEC, and scaled it to 7 and 28 MHz.  The free space gains
and patterns were substantially identical (to a couple of hundredths of a
dB) to those of the reference antenna (at 50.1 MHz), which I took to mean
that the scaling was substantially OK.

Next, I modeled the 10-meter yagi at 50 feet above an average MiniNEC
ground.  It showed 14.99 dBi gain and 9 dB F/B ratio.

Then I added the 40-meter yagi to the model above the 10-meter yagi at
various heights, with the following results:

40/10 hts (ft)		10m gain		10m F/B
---------			---------		-------	
80/50				15.46 dBi		9.5 dB
70/50				15.28 dBi		10 dB
60/50				14.03 dBi		9 dB

I'll leave the interpretation to you, except to note that according to
NEC-2, the 10-meter antenna is clearly "seeing" the 40-meter antenna above
it as far as 30 feet away.


73, Pete N4ZR
Contesting is!

The World Contest Station Database 
is waiting for your input at
http://www.qsl.net/n4zr 



--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com