[TowerTalk] average spacing improves array

[Dinsterdog@aol.com]

If you don't care much for 4-sqrs, ignore this post- hi

Ok, my original dipoles on my K8UR type 40 meter 1/2 wave array were about 5 
feet from the top of the mast.  But we changed that today-

Using an assortment of rope, K0RF showed my a way to make the dipoles more 
vertical, by pulling out a portion of the top of the dipole, so that the 
majority of the top half of the dipoles are further from the top of the 
tower.  Yet, we were able to keep the feedpoints of the dipoles,  at the same 
distance from the tower, thus, insuring the 4-sqr pattern.  All the while, 
improving the average spacing between the antennas.

We simply tied a rope about 10 feet from the top of the tower to the the top 
of the dipole,  and ran about 300 feet of twin out from the tower and tied it 
to T-posts.  On a 65 foot tower, this resulted in the majority of the dipole 
hanging down almost vertical with just a bit of the dipole, where it was 
pulled out from the tower, horizontal. 

We then took the bottom of the dipoles and pulled them as straight down from 
the feed points, about 25 feet from the center of the tower, down to about 4 
feet off the ground.  We then tied twine about 4 feet from the bottom of the 
dipole, pulling it away from the tower, and folded back the rest of the wire 
towards the tower. 

So instead of a sideways V shape, the dipole is in a 1/2 square shape, with 
most of the dipole being vertical, except for about 5 feet at the top, which 
is almost horizontal, and about 10 feet at the bottom, which is also 
horizontal pulled back towards the tower, held in place by twine tied to a T 
post away from the tower-.

So what did this do?  Well, by having the ends of the dipoles around 30 feet 
apart at the top of the tower, vs 10 feet, and having most of the dipole 
vertical vs a sideways V shape, two things happened.

First, we saw greater effects of mutual coupling.  The array's resonant point 
jump 135KHz, vs  no jump from the other configuration, similar to that of a 
K8UR design. So it had a big effect you could measure-  

But not a lot of difference on F/B.  However, the computer model shows a 3-4 
dB improvement.  My guess is that the 4 sqr will be better now on DX reports, 
hopefully, by at least an S-unit.  

Why?  Well, if you look at the average distance of 40 meter 1/2 wave dipoles 
tied to the top and bottom of a 65 foot tower, with the ends tied close to 
the tower, lets say 5 feet from the top and about 2 feet at the bottom, and 
the feedpoint of the dipole pulled out around 25 feet, it's a lot less than 
the average distance of dipoles pulled out in a 1/2 square pattern.  

The model shows around 2-3 dB improvement, or about an S-unit- we shall see 
although a side by side comparison is impossible-

Of interest, where I was getting 2-4 s units better reports on my 80 meter 
1/4 wave vertical 4 0sqr vs my Butternut HF2V, I am still only getting 1-3 S 
unit better reports on the 40 meter array vs the Butternut vertical.  But 
then again, the Butternut HF2V is a lot better 40 meter antenna then it is a 
80 meter vertical, hi-  

Another side note, the minimum power dump of the 40 meter array slightly went 
up from less to 1/2% to around 1%.  Not much, but annoying-   

If you have a K8UR array, you'll need a ton of space to make dipoles somewhat 
vertical in a 1/2 square configeration vs the diamond shape pattern,  but the 
model say's it might be worth the efforts- 

So next time some asks you why the resonant point in a K8UR array seldom 
jumps vs a 1/4 wave vertical array, you can reply perhaps it's due to the 
average spacing of the elements.  We proved today that the greater this 
average,  the more effects of mutual coupling you will see regarding the 
resonant jump.    

At least thats what our results suggest-  73  Paul  N0AH

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