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