Aastra RFP 32 User Guide DECT Site Survey Kit (EMEA) - Page 43
tions, and considerably improves the connection quality.
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Basics The same principle applies to all antenna types: The narrower the horizontal and vertical radiation range, the greater the distances that can be covered. In this connection we talk of antenna gain, which indicates the ratio of the energy radiated in a particular angle to the radiated energy of a standard antenna (usually a l/2 dipole antenna). An extreme example of this is the radio relay antenna, which is used for transmitting radio signals in a targeted direction from one point to the next. Note When using external antennas, the cable length between base station and antenna should be as short as possible because the attenuation of the radio signals in send and receive direction is not to be neglected in this frequency range (approx. 1.5dB per meter for a normal cable). A 4-meter long cable thus compensates for an antenna gain of 6dB. In any case it may be useful to consider using a special low-attenuation cable. Fading Effect If an base station is operated with external antennas, an antenna must always be connected to each of the two antenna connections. The antennas should have the same radio characteristic and also cover the same range. This reduces the occurrence of fading effects (caused by radio signals cancelling one another out through reflections), and considerably improves the connection quality. If such an effect occurs on one of the antennas, the base station automatically switches over to the second antenna, thereby preventing minor drop-outs. This is referred to as antenna diversity. Fading effects occur mainly inside and between buildings, which provide a great deal of reflection surface. Dual antennas inside a single housing, designed specifically with this effect in mind, are widely available in the market. That is why the base stations themselves are always equipped with two internal antennas. 41