It was stated that because the Superantenna loading coil is wound on (plasticized) PVC the losses are "excessive." Let's quantify the loss. Running 100 watts in a typical installation at 7MHz I estimate

** less than 5 watts **of loss in the coil PVC form.

Disclaimer: This is a a ball park estimate based on some simplifications, such as the coil current being the same at all points and the capacitance being calculated for an infinite block.

The antenna resonates at 7 MHz using a 6' whip. Using EZNEC we see that the loading coil reactance is 1400 ohms.

From the Superantenna photo I estimate the number of coil turns is 60 and the diameter is 1.5 inches.

For system losses of 25 ohms the coil current at 100 watt is 2 amps.

The voltage across the coil is 2A x 1400 ohms = 2800V

The maximum voltage between adjacent turns is 2800V/60T = 47V. The average voltage is 23.5V. I'll use 0.7 x 47V = 33V so the loss works out correctly.

The capacitance between adjacent turns is less than 20pF. That is if the coil is embedded in a block of plasticized PVC. Let's calculate the losses worse-case and call it 20pF. If anyone is interested I'll post the method to calculate the capacitance.

The capacitive reactance between adjacent turns is 1140 ohms.

The displacement current between adjacent turns is 33V/1140 ohms = 29mA

The dielectric loss resistance between adjacent turns is 1140 ohms X 0.1 = 114 ohms. The loss tangent of 0.1 at 7MHz is interpolated from a paper by G3YNH.

The power loss between adjacent turns is (29mA)^2 x 114 ohms = 96mW

The total dielectric loss is 96mW x 60 turns = 5.8 watts

Because some of the displacement current goes through air the actual dielectric loss is less than 5.8 watts. Let's be generous and call it 5 watts.

Links:

http://g3ynh.info/zdocs/comps/part_6.htmlhttp://newsuperantenna.com/MP1-SuperStick-Portable-Vertical-Antenna-Deluxe/