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the cushcraft r4/r5/r6000/r7/r7000/r8 are half (1/2) wavelength vertical antennas (as well as mfj/hygain av clones) -- not 3/8 wavelength (lambda). both antenna mfg. advertise these models as 1/2-wave.
they are based on the original cushcraft ringo design.
this is from av-640 installation manual :
the av-640 hf multiband vertical antenna consists of an end fed radiator that is
resonant in the 6, 10, 12, 15, 17, 20, 30 and 40 meter amateur frequency bands.
resonances on each band are the result of impedance matching a 3/8
wavelength element with a broadband rf transformer. the characteristic
impedance at the base of the 3/8 wavelength radiator is in the order of a few
hundred ohms.
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the center radiator of the av-640 supports 1/4 wavelength stubs for 6 , 10, 12
and 17 meters. the stubs are placed approximately one tenth of a wavelength
(electrically 1/8 wavelength) above the av-640 base. at the top of each stub the
impedance is very high at the frequency the stub is tuned. this high impedance
stops, (chokes) rf at this point creating a resonant 3/8 wavelength radiator.
