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Antennas |
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A good receiver doesn't offer the same efficiency if it doesn't have a suitable antenna. This is an essencital item in the listening of shortwave stations, and its choice is dependent on the receiver utilized and on the station listened. The portable receivers generally have a built-in telescopic antenna that is suitable to the listening of the stronger stations. These receivers have sensitive input circuits that are matched to that antenna. When an external antenna is connected to the receiver spurious signals can appear, that are generated internally in the receiver as a result od overloading. The communication receivers don't have a choice: an external antenna is neccessary, since that receivers don't have a built-in antenna. However, there isn't guarantee that the receiver can handle everything that is being pumped in to it. Any antenna that is put up will be not only receiving the signal that you are trying to hear, specially with antennas that receive a wide range of frequencies. There are several types of external antennas that can be used. Amateur radio antennas aren't ideal for shortwave listeners, because some of the criteria which make an antenna good for the amateur radio operator (like radiation, efficiency and standing wave radio) are somewhat different when it comes to reception only. And the highly directional antennas not really are a good idea. For the shortwave listener, passive antennas typically are thought of as wire antennas. Some types of passive antennas are: dipole, ramdom wire, loop, vertical, beverage. Active antennas solve a number of problems immediately. Few people have the space to hang a dipole of about 30 meters to match their interest in the 60 meter tropical broadcasting band, for example. They often take the format of a telescopic whip which can be unobtrusively mounted on an outside wall. Some safety points to consider:
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