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At 80 meters, a 102' G5RV is a bit short of the half wave. A doublet of this type would typically employ some multiple of quarter waves of total wire to insure a resonant feed. What was missing on top was put into the feedline. Transmatches were used which could handle the low and high impedances encountered.
G5RV chose a total length that presents reactance to the coax at almost every multiple. The impedance at that point is manageable with a transforming coax and pi-network. But the connecting of coax, an unbalanced feeder, directly to parallel line, an inherently balanced feeder, was pure rebellion.
When parallel line is balanced, it attentuates any radiation by at least 60 db. The traditional doublet radiated only on top. The G5RV arranged to let the feedline currents radiate by unbalancing the system. The result is cross-polarization, both vertical and horizontal currents.
Not long ago, a young ham told me that he compared the G5RV to a 'resonant' dipole and found the dipole to be superior. It turned out that he was not using a G5RV at all. He was feeding the 102' doublet with coax and a balun. The band of observation was fifteen meters.
I explained that the G5RV on fifteen would have four currents on top and be more omni-directional than the half wave dipole. The half-wave would have one current on it and fire, for the most part, broadside. Furthermore, the use of a balun on the 102' doublet defeated the feedline radiation and eliminated the cross polarization.
When the G5RV was introduced, there was little discussion of feedline radiation. Coaxes were attached to horizontal dipoles and quarter-wave verticals as though RF would appear only at the antenna. This may be why the term 'rf' ground continued to proliferate well after the time of Marconi. Because a coax-fed vertical, for example, will load the outside of a coax shield with RF even as it runs perpendicular to the array. Grounding the station was a way of forcing these RF currents to ground, not a practice I recommend. There are better ways to deal with the RF while grounding is all about safety. Be sure to read: "What's Ground Got To Do With It?"
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