Many amateurs like to operate on 3.7MHz for European contacts and 14MHz for DX, but do not have room for the 40m span of a half wave 3.7MHz dipole. Shorter lengths can be made resonant by including coils, or traps if the antenna is also to be used on higher-frequency bands, but both narrow the 3.7MHz bandwidth and increase losses. Capacitive end loading is better. It also shortens the required span, can provide a good feeder match on a second band, and greatly reduces the named disadvantages. A given amount of end loading has different effects on different frequencies. By separately varying the length of the radiator and the amount of end loading, an antenna can be set up to resonate and have a low impedance feedpoint on two frequencies, eg in the 80 and 20m bands.
展开▼
