Antenna Design
Antenna Design Software

Design of Antenna Traps Using a Solenoidal Coil of Coaxial Line

Author: R.J.Edwards G4FGQ © 7th July 2002

This program allows a practical designer to do what he normally does - wind some turns on a coil former and then vary number of turns until the resonant frequency with internal self-capacitance is the value required. Predicting accuracy is as good as the accuracy of measuring coil dimensions: 1 or 2 percent.

The trap is designed around solid polyethylene-insulated coaxial line. Any line impedance may be chosen but a low value is preferred. Since an antenna trap is subjected to the full transmitter output power it should be remembered low loss is associated with greater over-the-jacket line diameter. This sets the pitch.

The only advantage of coax traps is that a separate high-voltage, high current capacitor is not needed. But each trap must have its line length adjusted precisely for exact resonant frequency. If necessary a very small high voltage capacitor can be connected across the coil. Samples of line, nominally of the same type may vary in Zo which is a critical input parameter. A 1% error in Zo will result in a 0.5% error in prediction of resonant frequency.

Determine resonant frequency with a central 1-turn link plus antenna analyser.

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 CoaxTrap 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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