In a message dated 1/19/2008 4:15:10 P.M. Greenwich Standard Time,
gdslagel@yahoo.com writes:
I've been using the HFTA software to try and get an
idea of the optimum distance to stack a couple yagis
for best performance. I'm stacking 10/15/20
tribanders for increased performance. I was really
surprised that on most bands the optimum performance
seems to be with them separated by only about 10'...
for instance 65' and 56'! I expected it to be more
like 20' to 30'!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There is a caveat somewhere about this from N6BV. It is something
like...when using very close spacing (like 10 feet) for HF antennas, the HFTA
program
by N6BV will give false results.
If your top antenna height is going to be 65 feet, it would be in your best
interest to have the other at 32 feet if you are going to operate all bands.
It is a little too close for 20 but should do well on 15 and 10...assuming
you are running a garden variety tribander of normal boom length.
The HFTA is a wonderful tool if used with caution. Out here in a VERY
mountainous terrain N6BV's program was invaluable in designing my stacks. I
wanted to stack three KT36XAs but I found that with my terrain anything higher
than 90 feet was a total dud for 20 through 10 meters. The result will be
90/56/29. But, that was an optimization for my QTH.
I too was amazed with how much gain I could achieve with spacing of 10 feet,
until I read the instructions for HFTA. Generally you will need a minimum
of .5 wavelength for the stacks to start to play and from what I've read,
.65-.75 plays about the best. Of course this depends on boom length.
I hope this helps.
Bill KH7XS/K4XS
**************Start the year off right. Easy ways to stay in shape.
http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|