Traps

The tall onces: 5 windings and a 271 pF 2 kV capacitor in parallel, they resonate at 14.125 MHz, the small onces are similar, but the resonate in the center of the 40m band. You design them with the dipmeter program on the VNA. The Q of the LC circuit is not really large, the bandwidth of the trap is of the order of 1 MHz. The capacitor has to withstand high voltages, so get the capacitors that survive 2000 volt or more. Not sure to what power you can use them, but we will soon find out I guess.

A trap is stopper for a designed frequency, so you can cut a 40m antenna short with a 20m trap and a 80 meter resonant antenna short with a 40m trap. An antenna with a few traps is then in resonance at a couple of frequenties. On hindsight I like the large traps for the 20 meter band better than the smaller traps which are wound around PVC tubing. The large onces are made from an antenna to spanner cable separator, a piece of plastic 12 cm in length and 2 cm diameter, including two mounting holes suitable for a M4 or M5 bolt.

Last update: 14-oct-2017

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