On 6/16/2025 6:13 PM, john@kk9a.com wrote:
A fan dipole or the loaded dipole that K9YC suggested would have a consistent
pattern with no deep nulls and ~50 ohm impedance on the designed bands.
Yes, and this is a really important factor. The lobes are quite broad,
the depth of the nulls depends a lot on symmetry and surrounding
conductors. They're only very deep with very good symmetry, and because
the lobes are so broad, the only thing really matters more than about 6
dB is where the nulls are.
An important point about SWR. Especially on the lower HF bands, excess
attenuation due to SWR is a lot less than imagined. I load an 80M dipole
fed with about 160 ft of RG11 that's at 120 ft to work 60M, where legal
limit is 100W EIRP. SWR measured in the shack with an LP-100A is about
5.5:1, which works out to about 7.5:1 at the antenna. Total line loss is
on the order of 1.6 dB. The tuner in the KPA1500 happily puts about 150W
into the feedline with about 2W from the K4. The antenna plays quite
well, and I passed 100 countries on the band this winter. The only
activity on the band is FT8. The limitation on what I can work is the
limited number of countries active on the band and how well they can hear.
At this power level, the likelihood that high power arrestors would
fault prematurely depends on whether line length establishes a high
voltage at the arrestor.
73, Jim K9YC
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