I want to construct a small magnetic loop antenna out of copper tubing for the amateur bands 40 meter through 10 meter (7-30 MHz). The research I have done suggests that tuning can be achieved using a variable air capacitor with a range of about 10pF to 590pF. The literature suggests the danger of arcing across the capacitor. How can this be prevented? Calculations indicate voltage could reach as high as 4.4 KV. Since the voltage is highest at the capacitor, I would expect heat buildup at that point. How can I estimate the heat buildup over time in the copper loop when fed 100 Watts continuous power?