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  J/S  WB1GRB    1/5/2019




Fred Cunningham's (K1FC) Feedline Analysis Program, SWRPLOT
Download   plotswr.exe

Antenna Data

SWRPLOT uses data from an antenna modeling program such as MMANA to analyze the input impedance to a feedline across a frequency band. The modeling program is used to calculate the antenna input impedance for the top and bottom frequencies. Data for up to 10 bands can be entered. The program assumes a linear interpolation of the impedances. This may not work for some bands and those bands must be split.


Plotting SWR

The SWR will be plotted in the color selected. The plot color can be changed by changing the number in the box (0 to 14). If the INDEX COLOR box is checked, the color will increment after each calculation. This is to make it easy to spot changes or distinguish bands if all bands are plotted Full Width. You may also plot all the bands side by side. Delete the plots with Clear.

Numerical Readout

You can get a numerical readout by clicking on the plot. In addition to the frequency and SWR it will display the power out and the maximum voltage and current for a given power in. SWR OUT is the SWR at the load and SWR IN is the SWR from a specified source. Note that clicking recalculates the band selected.

Printing and Saving

The Plot may be printed with File/Print. If you exit by File/Exit the last data is saved in the file "last.dat." This data is restored on program start. Sets of data can be saved with an appropriate file name. Typing in ".dat" is optional when saving.

Downloads / Links


t is possible to calculate the output impedance from measurements of input impedance by entering the data including the frequency and clicking CALC Z OUT or to calculate a single point by entering the load data and clicking CALC Z IN.

Feedline Data

The feedline length is in feet. The velocity factor is in the form ".XXX" and the loss is in db/100 feet at a given frequency. Use the frequency datum closest in ratio to the frequency of interest. There are feedline data for some common coax and parallel lines. The user can add data to Linedata.txt for coax lines and LinedataP.txt for parallel lines. The feedline reactance and wavelength are calculated by the program.
Feedline properties can be found in the ARRL Antenna book and various online sources. Try to get information on the brand and type to be used. Some brands can vary from batch to batch.