Sunday, April 5, 2009
Plot of Impedance vs Frequency
For a wider view of W4BXI's 160m antenna properties I used the 4nec2 program's feature that plots impedance vs frequency. The above plot (click to magnify) is from 1.0 to 29.7 MHz in steps of 0.2 MHz. (I started at 1 MHz to get whole numbers on the x-axis.)
The color-coded points and scales identify resistance, reactance, impedance, and phase. A nice program feature is the display of numeric values when you click on a specific point. In the above example I clicked on the 7.2 MHz point before I made the screen capture.
This plot shows the repeating peaks and nulls of impedance, etc. as the program sweeps through the chosen frequency range (with a maximum of 256 steps). The corresponding Smith chart (not included here) shows a series of 16 circles passing through the calculated impedance points plotted around the chart.