Antenna Design
Antenna Design Software

Location, Type & Value of a Loading Component to Resonate an Antenna Wire

Author: R.J.Edwards G4FGQ © 4th March 2001

It often is required for the input impedance of an antenna wire, open circuit at its other end, to be purely resistive. In general, Zin has a large reactive component but this can always be 'tuned-out' by inserting a loading coil or loading capacitor at some position along the wire from the feedpoint. The type of loading component needed depends on the overall wire length and operating frequency. For lengths shorter than 1/4-wave a coil is necessary. The type of component and value for longer lengths depends on its location along the wire.

This program computes loading reactance and the corresponding values of L (uH) or C (pF) required to tune-out input reactance applying to a vertical antenna immediately above a good ground. Also to both halves of a centre-fed dipole.

Loading position is optional but it is usual to take into account radiation, coil loss and ground loss resistances. In this program all losses are assumed zero but errors in computing values of loading components will be small.

Maximum wire length is one wavelength at the wanted resonant frequency. Maximum (Length of wire to loading location)/(overall wire length) is 0.95.

Run this Program from the Web or Download and Run it from Your Computer
This program is self-contained and ready to use. It does not require installation. Click this link addaload then click Open to run from the web or Save to save the program to your hard drive. If you save it to your hard drive, double-click the file name from Windows Explorer (Right-click Start then left-click Explore to start Windows Explorer) and it will run.

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