[Boatanchors] Good (And Bad) Lengths For End-Fed And Dipole Antennas

[howard holden]

What is not taken into account with the antenna lengths presented is the physical calculated length vs the electrical length. From my experience this difference, if it is present, is more pronounced at lower frequencies. For those of you with unlimited property, no restrictions, etc., and can get your antennas high and in the clear, the only thing of potential concern is whether the wire is insulated or not, and even then it makes little practical difference. For those of us with the dreaded CC&Rs, physical limitations in placing antennas high and clear, or other factors precluding doing so, it’s a different story.

I speak from long experience, having the dreaded CC&Rs, faced with antennas that are very close to the ground, or in fair proximity to stucco, or fences, etc. My 40-meter end fed half wave, for example, is just 56 feet at resonance near the bottom of 40M due to the first 13 ft being an average of just 18 inches away from stucco. Because of this it is not usable on harmonics, which it would be if it were not near the stucco. My 80M dipole, spaced out 3 inches from a 7 ft high fence is just 122 ft long at resonance instead of the calculated 137+/- feet. And even then the resonant frequency can change when things are wet (fortunately a rare occurrence in Reno NV!) as ground or fence losses change with significant moisture.

If your installation involves any of these challenges, you may find the suggested lengths will not work so well.

73, Howie WB2AWQ/7 Reno NV


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From: Paul Christensen<mailto:w9ac at arrl.net>
Sent: Tuesday, November 24, 2020 4:48 AM
To: boatanchors at mailman.qth.net<mailto:boatanchors at mailman.qth.net>
Subject: Re: [Boatanchors] Good (And Bad) Lengths For End-Fed And Dipole Antennas

>Back in 2013, Jack, VE3EED (SK) published a scientific analysis of good and
bad lengths of antennas regarding ease of matching.  Basically, any length
of wire that was a multiple of 1/2 wavelength would present an extremely
high impedance (high voltage point) that will be very hard to match to any
transmitter OR trans-match."