What makes a _true_ 5/8 wave base antenna?

[StormWatcher365]

I posted this in the wrong (CB Radio) group, so I'll try again... I've been looking at 18ft. 1/2 wave, and 24ft. 5/8 wave base antennas... I've noticed some so-called 5/8 waves are adjustable to between [roughly] 16ft. to 22ft. How could this be 5/8 wave, does frequency become the determining factor?......... thanks, StormWatcher


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[Jay in the Mojave]

Hello Stom Watcher 365:



Yes I have seen this to, where some antennas are called a 5/8 wavelength antenna, are shorter or longer.



I agree with Doc there, approx 22 1/2 feet for a real true 5/8 wavelength antenna.



But looking at Eznec 3.0 a program for modeling antennas and such, shows very little change with the antennas performance over quit a range of lengths.



Some manufactures will use a .64 wavelength antenna, and I believe this is done to allow a simpler matching circuit to be used, without any real addational gain to the antenna.



And the shorter antennas that are advertised as a 5/8 wavelength antennas, and are closer to a half wave length, have the vertical element mounted in the base assembly, that has capacatance, that plays a part in the antenna matching circuit.



The 5/8 wavelength ground plane antenna should be .625 of a wavelength to be a 5/8 wavelength antenna, in my book. But as the matching scemes changes the lengths will also. Not a real biggie there.



Jay in the Mojave



www.a1antennas.com


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