[TowerTalk] XM240 addendum on interaction

AA4NC@aol.com AA4NC@aol.com
Sun, 11 Oct 1998 18:35:38 EDT

As I reported yesterday, I was extremely pleased overall with the Cushcraft
XM240, especially the SWR curves. Today we mounted a 5L 6m beam 5' below and a
4L20m beam 11' below the XM240. Even at these distances, there is some
interaction between antennas, although it actually improved the SWR on the
As measured with the MFJ 259 which was the most conservative meter that I
have, the 2:1 points went from 7.007/ 7.260 to 6.990 / 7.280 with the addition
of the other antennas. The FT990 and WM-1 meters also confirmed this shift.
I would assume that the pattern and gain were also affected, but I have no way
of measuring this.
This is something to keep in mind when stacking antennas. Even though 9-10'
stacking distance is recommended, there is still some interaction there,
although I doubt it is too detrimental. Moral: If you have a big mast - use it
(but not if it's aluminum !! :>)



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