Below are 3-D radiation patterns for selected frequencies. 2-D plots in the horizontal plane or vertical plane can also be produced for any azimuth or elevation angle. These are based on the source (transmitter) being connected at the midpoint of one side of the square loop. The default NEC modeling of a feedline assumes no radiation, so the patterns are unaffected if a feedline is included.
Click on any graphic for a magnified view.
 |
| 1.8 MHz |
 |
| 3.6 MHz |
 |
| 5.357 MHz |
 |
| 7.2 MHz |
 |
| 10.1 MHz |
 |
| 14.2 MHz |
 |
| 18.1 MHz |
 |
| 21.2 MHz |
 |
| 24.9 MHz |
 |
| 28.5 MHz |
Below are plots of SWR and feed point impedance (magnitude in ohms) for 3 different lengths of the loop: 528, 540 and 552 ft. The legend at upper right identifies each case by color of the plotted data curves. Each curve is based on 188 data points. Click on any image for a magnified view.
 |
| SWR vs frequency |
 |
| Impedance at feed point |
I've also analyzed the effects on SWR and impedance of including a feedline length with various lengths, but need to validate the results further before posting here. Previous analysis and measurements of an actual 80 m loop indicated that the SWR dips shifted toward higher frequencies as the feedline was shortened.
