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Marconi, I can not do more than speculate, but with respect to radials on a GP that are resonant length having some kind of pattern altering effect it would seem reasonable to expect so when you think of the changes in patterns that occur when two identical/similar Yagis are co-phased. Coupling is desirable in co-phasing setups, and this effect depends on resonant lengths of the two (or more) antennas in such cases, does it not, and if so, why would we not expect pattern shifts from similar length antennas near each other?


It makes sense to me that 18' long radials sitting above a horizontal Yagi would couple and alter the RF pattern. Properly co-phasing antennas for a desirably effective pattern begins at about a 1/2 wavelength apart, or for a compromised mobile setup, 1/4 wave apart, as I understand it, so an inefficient distorted pattern might be expected when co-resonant length antennas mount nearer to each other than 1/2 wavelength.


I will say that I had to retune the Yagi when I mounted the short radial 5/8 above it, and then retune when the radials came off. I did not retune when the Qv4k went up over it.


Just my thoughts, and certainly not meant to dispute anyone's experience. I do enjoy the tidiness of experience and science reflecting each other.