Building and Testing 50 MHz Traps for Antenna Experiments
Building and testing 50 MHz traps using FR-4 PCB and RG-58 coaxial cable.
Description
EA4EOZ details the construction and testing of 50 MHz traps, a critical component for multiband antenna designs. The project addresses the challenge of sourcing high-voltage capacitors suitable for trap applications, exploring alternatives to expensive doorknob capacitors.
The author successfully fabricated a capacitor using 1.6mm double-sided FR-4 PCB material, achieving a capacitance density of 2.6 pF/cm2. Utilizing the VE6YP calculator, specific L and C values of 30 pF and 0.31 uH were determined for a 2cm diameter coil. Both the FR-4 PCB trap and a coaxial cable trap, constructed from RG-58, were built and tuned to approximately 50 MHz using a spectrum analyzer. The coaxial cable trap demonstrated superior performance, exhibiting a notch nearly 20dB deeper than the FR-4 version.
This practical comparison provides insights into trap construction for experimental antennas, with the coaxial cable trap selected for an antenna project intended for operation at up to 100 watts.