[TowerTalk] modeling a v shaped dipole

[Gary Slagel]

Thanks Jim,
 
I'm wondering if I can take advantage of this to create a switched, 3 legged antenna that will have the same gain/pattern as 2 switched broadside dipoles.   Looking at the diagram below, I'll switch from using wires 1 and 3 for a northeast/southwest pattern to using 2 and 3 for a northwest/southeast pattern.  This would work nicely for me cuz there's a big cliff to the north side of this setup so I can't get a support out that direction.... not to mention less wires to hold up in the air.  Does that make sense?  Again, it all depends on the vee enclosing a 90 degree angle being just as efficient as a broadside dipole! 
 
 
                              north
-------------------------------o  o--------------------------------
            1                   |                2
                                 |
                                 |
                                 |  3
                                 |
                                 |

Gary Slagel/N0SXX
Hot Springs, SD
http://marina.fortunecity.com/sanpedro/351

--- On Fri, 9/25/09, jimlux <jimlux at earthlink.net> wrote:


From: jimlux <jimlux at earthlink.net>
Subject: Re: [TowerTalk] modeling a v shaped dipole
To: "Gary Slagel" <gdslagel at yahoo.com>
Cc: "TowerTalk" <towertalk at contesting.com>
Date: Friday, September 25, 2009, 11:03 AM


Gary Slagel wrote:
> I didn't do a very good job of describing the antenna.  I'm not really folding the ends back into a C.   I'm making a flat V.... like an inverted Vee but with the ends horizontal rather then drooping to the ground.  
>  
> I didn't expect much effect as I brought them back to enclose a 135 degree Vee but I was surprised that when the Vee was enclosing only a 45 degree angle, EZNEC still showed it with an identical pattern to a broadside dipole.   So... if the pictures I drew below are understandable, I wouldn't have thought these two dipoles would have an identical azimuthal pattern!
>  
> ----------------o o---------------- broadside dipole viewed from above
>  
>                 o o               45 degree vee dipole viewed from above
>               /      \
>             /          \
>           /              \
> 


Oh yeah.. the pattern will be almost identical.. The "phase center" of 
the bent dipole is about 1/4 to 1/3 of the way from apex to tails, 
depending on the angle.



Think of the far field as being the sum of the fields from a bunch of 
little chunks along the antenna.  When you bend it, the direction of 
current is slightly different, but since it's matched on the other side, 
the "off center-ness" cancels.  So now, all you've really got is the 
same as if you had a sort of stepped dipole (with magic non radiating 
interconects):

                 o o
               -     -
             -         -
           -             -



_______________________________________________





Gary Slagel/N0SXX
Hot Springs, SD
http://marina.fortunecity.com/sanpedro/351