Radio waves behave like light, travel in straight lines and are in principle limited to the horizon. However, just like light they may be reflected and refracted, and this can happen in the D, E and F ionised layers that extend from 50 to 400 km above the surface of the earth. The layers are created by the rays from the sun and absorb and reflect radio waves depending on their frequency, the solar activity, season and time of day, affecting the propagation.
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UniWave Di-Wave 100 with ferrite and telescopic antennas.
Internal antennas are not sufficient for weak stations and an external antenna must be used. The cheapest solution is a 10-12 metre copper wire to a tall tree, preferably with a transformer balun some dis-
tance from the house connect-
ed with a shielded cable. The strongest signal is achieved with an antenna tuner that matches the antenna system at the actual frequency. The necessary parts may be bought individually or in kit form with pre-cut wire lengths.
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Thieking wire antenna with RF-Systems MLB balun.
A loop antenna is a magnetic device with directional properties that is capable of suppressing interfering stations at the reception frequency. The antenna is largely insensitive to electrical noise fields and may also be used indoors. A shielded loop antenna can be built from plastic tubing and coaxial cable, but requires tuning with a capacitor at each frequency. The most versatile solution is a ready-made loop antenna with an integral broadband amplifier.
>> Using the loop antenna
Wellbrook Communications active loop antenna LFL 1010.
An antenna with amplifier may be located on the roof of a house or car, connected with shielded cable. Thus the anten-
na can be kept clear of the electrical noise that would interfere with its performance inside. A good match is also achieved between the integral amplifier and antenna whip even at short antenna lenghts. The power supply is always placed indoors and often feeds the amplifier through the cable. Good active antennas are somewhat expensive.
>> What is an active antenna
Procom AAC 1 10 kHz-110 MHz active outdoor antenna.