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Losses in shunt-fed towers
HV loss is hard to estimate. You could make your shunt wire a shunt tube or
rod and basically eliminate corona (A rule of thumb is that 10-15 kV/cm radius will have virtually no corona.. so for your 6kV, a 1cm diameter tube is in the right ballpark) Skin depth at 3.5 MHz in Aluminum is .043mm, and the usual rule of thumb is to make the tubing wall thickness 3-5 skin depths. 0.12-0.20 mm seems about right. Copper could be thinner wall (skin depth is less) I presume that the corona effect should be visible at dark. So far I have seen none, but we had not a single day of rain since I mounted this antenna (incredible summer season...). So, I must verify when rain will come, in a few days from now they say. Or do you think that corona may not be visible? I am using a 4-mm diameter wire so, if I will really have corona problems, I could insert the (vertical) wire into a 1-cm aluminum tube connected at the very bottom of the wire (i.e. at the antenna feed point). Probably a 2-meter long tube could be sufficient (RF voltage gradually diminishes getting away from the antenna feed point). 73 Tony I0JX |
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