[AMRadio] l00p antenna


Geoff w5omr at w5omr.shacknet.nu
Sun Jan 9 13:09:03 EST 2005


While I'm posting messages here, I have a question for the 
consortium...  I've posted this in another group, so just gonna 
cut-n-paste it here.

-------------------------------------
It is my intentions on putting up a new antenna.  A Loop.  I 
ordered a 100' roll of 18ga 450 ohm ladder line, and it came in 
this past Thursday.  I already had a 500' spool of 12ga pull-thru 
wire that I recently obtained at a local home improvement center. 
  The plan is to lower the current Inverted Vee, change the coax 
out in favor of the 450 ohm ladder line, then add another 120+ 
feet of wire from one end of the Inverted V end to the other, 
creating a 240+', pulled apart, folded dipole (aka; Delta Loop). 
  That's the plan.

My house sits basically in the center of the property.  The lot 
dimensions are 60'wx130'd (maybe slightly less).  The long parts 
of the lot point North and South.  The Inverted Vee (and any 
other antenna I put up on 75m) will have to be broadside East and 
West.

The tower is sunk in 1 full yard of concrete, in the center of 
the lot, but in front of the house.   In order to feed the 75m 
Inverted Vee in the middle of it's 120' length, I have to support 
one leg, off of center where the feed point is, with the feed 
point directly over the top of the house.  When I put the loop 
up, I want to be able to pull the feed point up to it's apex. 
The feed point will be at/about 65', while each end will droop 
down to around 20'.  The bottom part of the Delta Loop will be 
flat, across the lot, from one end to the other.  This also means 
that there will be more wire on the north side of the tower (over 
the house/back yard) than on the South side of the tower (over 
the front yard, toward the street).

The question is, is it going to matter, in a delta loop antenna, 
where it's fed?  I understand about changing the polarity from 
vertical to Horizontal, if you feed a Delta say, in the corner of 
the loop.  Would I be better off feeding the antenna in the 
middle of the bottom flat stretch of wire, or continue with 
feeding the antenna at the highest apex?

I know experience is the best teacher, and more than likely the 
answer will be "try both, and see which one works best for you" 
and in all likelihood, that's probably what I'm going to do.  But 
if someone already has been down that road and has come up with 
some conclusive evidence as to why one way is better than the 
other, I'm all ears.
Thanks for yours.

http://w5omr.shacknet.nu/~w5omr/hamstuff/loop/loop.JPG

73 = Best Regards,
-Geoff/W5OMR




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