[TowerTalk] Rain drops noise on Yagi (dipole)

[David Robbins]

"Taking the worst case rain static situation – very heavy rain for say, about 30 minutes, the Top antenna is ~ @ S9, the 2nd @ S6-7, the 3rd @ S3 and the bottom antenna quiet or almost quiet."

First we should note that it is not the rain that creates the noise... the rain or snow is a symptom that may or may not accompany the noise.  The noise is caused by a high voltage gradient between the earth and cloud which causes charges to accumulate on the higher parts of a tower/antenna and when enough charge accumulates corona starts... it is the corona that you hear as the static.  It is very possible to have corona with no rain or snow at all, and it is possible to have heavy rain or snow with no corona.  It is possible to predict with reasonable certainty if a particular storm will create corona, after many years of watching radar and correlating with local conditions.  I am pretty good at predicting here, but wouldn't try to do it in other parts of the country.  Corona is most likely on ends of elements and sharp pointy things as those are the places where the voltage gradient is the highest.

As far as preventing it, that can be difficult.  Telrex tried adding rounded balls to the ends of their elements for a while, but didn't round off corners of t-match shorting straps or even the screws connecting the element sections so did not solve the problem on their antennas.  I think most of the quads that claim to be quite probably had insulated wire, which combined with relatively few pointy things like screws or hose clamps would reduce or prevent most corona.  Dipping a driven element in liquid rubber might be an interesting experiment, but I would like to see a UV camera used on a Yagi during a storm to see just where most of the corona is first, there may be simpler solutions, or maybe not.


David Robbins K1TTT
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