Bifilar-Wound Antenna TrapsAuthor: R.J.Edwards G4FGQ © 1st August 2002
Note: This program should be considered experimental. Only one trap of this kind has been constructed and measured by the author as a check for program errors. No traps have been connected in an antenna for performance checks.
Two identical plastic-insulated wires are wound together on a former (as with a bifilar RF choke). The two wires are then connected series-aiding. The inductance resonates with the distributed turn-to-turn capacitance at the trap frequency which is set to the exact value desired by adjusting fractional coil turns. A high-voltage, high current, tuning-capacitor is not needed. An overall length/diameter ratio in the range of 1.5 to 2.5 is recommended.
Make the diameter over the wire insulation roughly two or three times the wire diameter. Polyethylene and Teflon are the best insulants in high-power applications. Use stranded wire.
The resonant frequency is best checked with a one or two turn loop of thin wire around the centre of the trap with a 6-inch long pair of wires to an antenna analyzer switched to its impedance range. Slowly vary the frequency and search for a very sharp peak in impedance magnitude to find the resonant frequency.
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 TwinTrap 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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