Topband: PHASED VERTICALS

[Bill and Liz McHugh]

I have just completed installation of a second vertical to work with my first one, using the Christman feed method.  Everything works well end-fire: very low SWR, about 3 S units F/B.  But the bandwidth is MUCH wider than I had expected.

Each vertical is 80 ft top loaded with three 36 ft wires each, the antennas are spaced 1/4 wavelength, each has 64 radials under it ranging in length from 40 to 135 ft, each shows a 2:1 SWR bandwidth of about 80 khz by itself when the other antenna is left floating.  Both verticals show R=40-45 and X=5 with SWR 1.17:1 at point of resonance.  The array in either end-fire mode is significantly broader than 80 khz....more like 150 khz or more.

Is it possible that the top-loading wires are creating a mutual coupling situation which broadens out the response curve?  Has anyone had a similar situation using phased top-loaded antennas?

BTW the 1820 khz resonant point on each vertical rises to 1860 when the antennas are phased, and I believe this is a normal situation.  Though I am feeding the antenna through a 50 to 28 ohm unun which seems to provide very low SWR on end-fire, on broadside the SWR is about 2.1:1, which is about what one would expect, and I am currently attempting to solve that problem.

Any input on this would be most welcome. 

Bill, VE3CSK