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About ten years ago, or so it seems, I started an indoor antenna project for the benefit of many who will not wish to build an outdoor antenna/transmitter. Despite much time going by, the project continues.
What we are dealing with is an AMT3000 modified according to the manual instructions and a self-built loading coil which happens to be triangular rather than circular. It is my understanding that a coil does not need to be circular, and can even be rectangular if so desired.
I name this the “Tri Coil”, which is the name I’ll use.
Right now I get the peak at 82-turns on the Tri Coil, but the antenna has changed properties and brought the RF output DC reading down from the optimum 13VDC to a lower 10VDC. This is because of many days of rain.
The antenna is somewhat goofy, but does the desired job very well. It is mainly a metal window frame. Yes, about a 6-foot window. I call it the Wintenna, and its advantage is that it lays the signal both indoors and outdoors without requiring the transmitter to be outside in the weather. But the weather does cause it to change values.
The next tap lower is at 72-turns, the next higher is 88-turns, both of which are way off peak.
The next step is to find if the peak point can be improved by adding or subtracting a few turns of the coil, up or down from 82.