[TowerTalk] Stacking Dissimilar Antennas

[sawyered at earthlink.net]

I have a 3el 15M Beam on top of my tower that is stacked with an 8 el 15M beam at 30 feet when pointed NE and a 5 el beam at 50 feet when pointed south.  None of the booms are the same length.  You need to compensate for the boom lengths and NOT use equal length coax (as you would identically stacked antennas).  The difference in length of coax is the free space wavelength of the difference in boom length and then coverted into physical length of coax using your Vf of the cable in question.

Essentially, you want a "receiver" to see perfectly in phase signals from the 2 antennas and the only way to do this is to lag the shorter boom antenna a little until the longer boom antennas signal is crossing the point on the tower where the shorter boom feed point is.  Then launch the shorter boom signal.  Now they will be in phase and essentially work like they are identical and stacked.

By the way, IT IS WORTH THE EFFORT.

73

Ed  N1UR