Often it's not possible to erect a full 1/4-wave vertical, especially on 160m or even more so at 600m. It appears that we will be getting a 600m band 472-479 kHz where the wavelengths is about 2000'. That makes the antennas a serious challenge. I've written the following article on verticals with heights between 0.05 and 0.125 wavelengths. The modeling was done at 1.83 MHz but most of the discussion uses dimensions in wavelengths and is applicable at any frequency including 600m. The discussion illustrates how critical the height of a vertical is and the absolute need to use some form of capactive top-loading if any reasonable efficiency is to be achieved. The article focuses on the mult-wire umbrella type of top-loading but also discusses the critical issues relating to ground systems and conductor loss. As I always try to do, the article includes some experimental confirmation of the NEC modeling results. Download Short 160m verticals
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