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
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|