Well, Glenn, I would lean toward voltage-feed at the base, since you have that insulated tower! Because of the lower current, the ground-losses would be minimized, and the current maximum would be fairly high on the tower, resulting in a nice low-elevation angle, omni-directional radiator for long haul 80m DX work. Of course you would need a robust tapped parallel LC network with a robust inductor, probably mad of copper tubing and a really high voltage air variable capacitor, or better, a vacuum variable and there would be some substantial switching challenges to switch the feed between 80 and 160, that would be avoided with your trapped top loading approach, but full-power 80m traps 90' in the air are non-trivial components also! I LIKE the voltage-fed 1/2 wave vertical approach and have had wonderful success with it on 40m, where I fed the vertical 1/2 wave through a 1/4 wave 450 om line for an almost perfect match!! Great antenna. And I used it as the driver for a wide-spaced 3-element vertical 40m yagi for Peter 1 Island and Bouvet and it was a killer antenna for SE Asia on the evening LP.
So, that's my $0.02! If it were me, I'd leave the top-loading alone and do the work to voltage feed that insulated tower! Should be a great antenna for both 80 and 160, and has the advantage that all the tinkering and tweaking can be done at ground level! GL and have fun!! 73, Charlie, K4OTV -----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Glenn Biggerstaff Sent: Saturday, February 28, 2015 8:16 PM To: topband@contesting.com Subject: Topband: 160 Tower on 80 Hi all, I have a 90 foot Rohn 25 tower with an insulated base and insulated guy wire sections for top loading ,base fed for 160 meters. It work great ,but I would like to use it on 80 meters as well. The 3 ideas I have considered are voltage feed at the base with a resonant LC network at the base, but I am a little worried about the voltages present at legal limit power. Second idea,disconnect the top loading and put a trap between the top loading and the tower to divorce the top loading on eighty then an L network at the base for 80. Third idea, run a wire as a sloper either a quarter wave fed against ground or a 1/2 wave dipole from the tower. Any thoughts or alternative ideas would be greatly appreciated. Glenn WW4B _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband