Antennas

Trap Dipole (1)

  • A 7 MHz half wave dipole fed with a balanced line will look like two end fed half waves on 14 MHz; feed point impedance will be very high and consequently there will be a high SWR on the feeder
  • To construct a dual-band antenna a parallel resonant circuit called a trap can be inserted in each half of the antenna, constructed from a coil and capacitor
  • The traps are resonant at the higher frequency (14 MHz) and present a high impedance to RF energy at that frequency, effectively cutting off the parts of the antenna outside the traps