If you take a coax on a long run to ground from an upper story, its own
capacitance per foot is going to bypass RF from the inner to the shield. If
you connect capacitors across one or both ends, you have added bypassing of
the RF from inner to the shield. Unless the coax happens to be an odd
multiple of a quarter wave line, you simply have both the shield and center
paralleled and effectively, the RF is on the shield as well as the center
conductor.
This may appear to improve your grounding, not from the coax "shielding"
your ground wire, but from the larger diameter of the effective ground being
the shield along with the center conductor. The detailed analysis depends
on the electrical length of the coax, and how far from earth ground, the rig
happens to be in terms of wavelength fractions.
The capacitance of coax per foot is pretty high, due to the solid
dielectric; it might be interesting to analyze the same run of coax, if it
were made of air dielectric coax cable.
Stuart
K5KVH
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