Insulation is not the theory behind a quad being less susceptible to
precipitation static. A quad does not sharp tips protruding into open space
making it less sensitive to noise caused by corona discharge.
John KK9A
From: Grant Saviers <grants2@pacbell.net>
Date: Sat, 8 Dec 2018 20:36:28 -0800
I agree with K1TTT's analysis. Another factor contributing to which antennas
are noisy is how the stack is arranged. If it is the classic "Christmas
Tree" layout with smallest yagi on top then that provides limited
"shielding" of the voltage gradient to the lower antennas. My stack has 80m
100' long elements on top and all below it are quiet.
I think geometry differences and/or a difference in the site matter. Yagis
have lots of discharge points, ie sharp edges. Quads usually don't and the
feedpoints aren't at the top and wire insulation may make a difference.
Also, note one recent TT post reporting that a ground wire around the
rotator bearings tamed the noise. A ball bearing oil film has a breakdown
voltage around a few dozen volts, in my experience. So if there is arcing
across the oil film the entire mast and assembly is bouncing around in
voltage.
IMO it doesn't matter if the driven elements are grounded. A current in any
yagi element discharging voltage from its tip is going to introduce noise
into the driven element. The corona itself is a broadband white noise source
so can be picked up by other antennas. But the fact that lower ones can be
quiet tends to reinforce the idea that the current in the discharging
elements is the larger contributor.
Regarding charge accumulation from water and snow landing on the antenna,
there is a lot to learn from the aviation world. However, aircraft are
certainly contacting enormously more charged particles than precipitation
landing on an yagi. What is interesting are the devices added to aircraft to
dissipate the charge and eliminate radio interference.
Next time I have noise, I will check my top 4L SteppIR for its noise level.
It's on a tower separated from the stack. If the logic re quads is correct
then a SteppIR being fully insulated should be quiet.
Grant KZ1W
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