A. Ham radio enthusiasts generally expect an antenna to have a low SWR. Otherwise, they feel, “It won’t get out well and I might even damage my finals.” What’s your opinion? Is this a universal truth? Here, look at this:
Here the antenna is operated at or near its natural resonant frequency. This is the mode most hams are familiar with. At the operating frequency, the feed impedance is close to 50 Ohms resistive and an antenna analyzer shows a resonant dip. An antenna operating in resonant mode can usually be fed with coax directly, without a matching network.
Here the antenna cannot be fed directly with coax at the operating frequency, for it shows neither an impedance of 50 Ohms nor a low SWR at the feed terminals. Some form of external matching is required for an antenna operating in a non-resonant mode. Frequently it is an antenna tuner. If you are contemplating, for example, a 20-foot, no-radial, OCF DX Flagpole Antenna, take special note... It almost always operates in a non-resonant mode. Another, perhaps more familiar antenna that operates in the non-resonant mode most often is the popular 43 ft. vertical with radials. It is naturally resonant at 22.9 MHz, hence it does not show a low SWR or a 50 Ohm match on any ham band.
Therefore, do not attempt to feed a non-resonant mode antenna directly with coax. Some form of a matching system at the base is a requirement. Have you seen our DX Flagpole Antenna?