At 13:39 5/25/03 +0000, Barry wrote:
>I didn't notice any significant F/S until at least 90 degrees from
>the heading. I've heard others talk about 30-40 db F/B, but this is
>nowhere close. I'd like to hear others' experiences.
Barry,
A while back I evaluated the flag, pennant, diamond, and delta, as well as
the K9AY. Of all of them the delta configuration consistently produced the
poorest performance. It was the most susceptible to degradation caused by
nearby resonant objects and had the poorest F/B even when in the clear.
Yes, I know that the computer predictions differ, but I don't think anyone
has ever made an EZNEC to EZNEC QSO yet! And yes, I know that the delta
configuration is the easiest to build, but I'm sure you know there is no
free lunch. If you need to have a deep null with better F/S, you will
eventually wind up with the flag configuration. Why not just quit fooling
around and go right to it?
If you insist on making the most of the delta there are a couple of things
you can try. First off make sure that your matching transformer is the
isolation type of a known good design. Also make sure that the winding
insolation is not compromised. Any leakage between the windings will
decrease isolation and possibly cause unwanted IMD products in the band.
The other thing to watch for is to make the antenna as dimensionally
accurate as possible. Each wire length should be as close a possible to
EXACT length with no sags/droops in the span. Even small departures from
perfect symmetry will cause a dramatic reduction the depth of the rear null.
Good luck & 73,
Larry - W7IUV
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