Topband: 80M Dipole at 105 ft ?

[Donald Chester]

My base-insulated Rohn 25 tower is 127' tall, with 80m OWL-fed dipole attached at 119'. I use the tower as 1/4 WL 160m vertical (actually a vertical tee since the dipole adds considerable top loading), with 120 quarter-wave buried radials each 133' long. I tried loading the vertical on 80m as a half-wave several times, but stateside it has never been impressive at any distance. From Europe and the Pacific Northwest, my signal was reported to peak at about the same strength with both antennas, but with the vertical, the fades were much deeper.  The dipole always had the more solid signal. I never tried the vertical to KH6, VK/ZL or East Asia. I would have thought that with the extensive ground radial system, the half-wave vertical would have been superior for DX, but that has never yet been the case.

Using a balanced tuner, I can load the 80m dipole on 160m as a quarter-wave, but as expected, the vertical usually does better everywhere, except in the 25-100 mi. distance range.  In Nashville, about 50 miles airline from here,  the short dipole is about 30 dB stronger on 160m than is the vertical.

The OWL to the dipole runs up through the inside of the tower structure, spaced at the geometric centre of the triangle.  The close proximity of the feedline to the tower through nearly its entire length, closely couples the dipole to the tower when it is used as a vertical, even though there is no solid electrical connection between them.

Don k4kyv