 ```Dear Werner, LF Group, At 19:52 25/01/2003 +0100, you wrote: ``````At first sight it work FB Loop perimeter is 85 meters and 12 meters above ground Series coil is 1.5 mH series cap is home made butterfly 280 pf plate space is 20mm, current in the circuit is 3.5 Amp Cap and coil are in the shack , and two wires are going out through the wall widely spaced from the wall, and so straight to the loop . In the shack it smells like ozone Hi ```You didn't say exactly how the tuning components and TX are connected to the loop - but it seems to me that if there is a significant voltage between the loop wire and ground, the antenna could actually be operating as a vertical tuned against ground. Obviously the antenna radiates quite well, but it is not clear that it is actually radiating in a horizontal loop mode - 3.5A seems a low current for a loop antenna to radiate much signal. The highest possible radiation resistance would occur if the loop were circular - in that case the area would be 575m^2, giving Rrad of 0.44milliohms, and a very optimistic estimate of ERP of maybe 10mW, assuming none is dissipated in the ground or environment. I expect the loop will have an inductance between 100 - 200uH; If both the 1.5mH coil and 280p capacitor are connected in series with one terminal of the loop, and the other terminal is near ground potential, the loop wire will be at a low potential (with 3.5A , some 100's of volts maximum), and there will be little radiation in "vertical" mode. But if this is the case, with total L of 1.7mH, and C of 280p, resonant frequency will be about 230kHz or slightly more. If, on the other hand, the inductor is connected to one terminal of the loop, and the capacitor to the other, the whole loop wire will be at high potential, and there will be a large "displacement current" flowing to ground through the antenna capacitance, so one would expect the antenna to be operating primarily as a vertical. In this condition, the capacitance to ground of the loop wire would effectively be in parallel with the 280p tuning capacitance. Estimating this to be 6pF/m, 85m of wire gives 510pF, so 790pF total capacitance. With 1.5mH inductance, this gives a resonant frequency of 146kHz, much nearer reality! There will be additional capacitance due to the connections to the shack, which would bring the resonant frequency to 136k. In this condition, the voltage on the loop wire would be roughly 4.5kV, and the antenna would be predominantly acting as a vertical, giving roughly 300mW ERP, again assuming no environmental losses. ```Cheers, Jim Moritz 73 de M0BMU ```