When I lived in Northern Illinois I had a 110' tower (A fold-over non
guyed, aluminium Heights tower). For 160 & for 80 I had shortened
delta loops with the 160M apex held off 1' from the top of the tower,
the 80M apex was about 3 feet lower. I had servos inside which
controlled a vacuum variable at each feed point, this gave me 1.1
resonance throughout the bands.
Towards the end of my time there I replaced the servos and those
vacuum variables with some mounted Vacuum variables attached to
motorized assemblies I bought from Fair Radio. They were not easier
to use than the servos, the servos allowed you to instantly feel when
you reached the end of travel and the Groth counters I used made it
easy to plan where to set the adjustment to.
If I weren't concerned about covering all the band it would have been
easier to adjust them for one part of the band and leave them there.
A taller tower would allow a larger delta loop and greater bandwidth.
They certainly must have had some directivity and I'm sure other
ideas would have worked more elegantly but it worked great. I never
had trouble making DX Q's across the globe and it was a very nice
antenna all considering.
73,
Gary
KA1J
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