Ham Radio-How an Antenna Trap Works
Heres a great video about making traps for your HF aerial by W1GV, trap dipole is easy to make and if you build not only will you save money you will learn too.
Traps are no more than parallel tuned circuits placed on your radiator to stop a longer piece of your wire from upsetting the tune.
Stan shows how you can build a trapped array placing a trap on a ten-meter dipole to extend its coverage to twenty meters, I have a system similar to a trap single trapped vertical-it covers three bands-how do I do this-I place another trap in my case after the twenty-meter band I place a forty-meter trap, two traps give three bands.
The beauty of this arrangement is that you have one radiator with the traps fitted at different positions, traps shorten the radiator length so some experimenting will be required. An aerial like this does not need an ATU or aerial matching unit they are self resonating systems and they work very well.