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r <br />* # tir EXECUTIVE SUMMARY * * * <br />Amateur Radio communications between two <br />distant points on the earth rely on signals propagating <br />through the ionosphere. Acting as somewhat of a mirror <br />at heights in the order of 150 miles, the ionosphere <br />returns signals to the earth a thousand or more miles <br />away. <br />The vertical angle of radiation is the Key factor in <br />determining effective communications distances beyond <br />line of sight. For the greatest possible communications <br />distance, the energy from the transmitter must be <br />rad.ated at angles close to the horizon. For this to take <br />place, a horizontal antenna must be placed high above <br />the ground in terms of wavelengths. The length of a radio <br />wave is inversely related to its frequency. <br />A beam type of antenna at a height of 70 feet or <br />more will provide greatly superior performance over the <br />same antenna at 35 feet, all other factors being equal. <br />To a distant receiving station, a transmitting antenna at <br />70 feet will provide the effect of approximately 3 to 4 <br />times more transmitter power than the same antenna at <br />35 feet. Dependin'^ on the level of noise and interference, <br />this performance disparity is often enough to mean the <br />difference oetween making distant radio contact with <br />fairly reliable signals, and being unable to make distant <br />contact at all. Thus, the antenna at 35 feet is un­ <br />satisfactory, while the same antenna at 70 feet is quite <br />satisfactory. The 70-foot height is used only for the <br />purpose of illustration, however, and should not be <br />constiued as the optimum height for antennas. Heights <br />above 100 feet will give significantly better performance <br />than at 70 feet. <br />If an amateur operator is restricted to the use of low <br />antennas, it is reasonable to assume he will obtain more <br />powerful transmitting equipment to compensate for the <br />loss of antenna effectiveness. For example, he might <br />increase his transmitter power from 500 watts to <br />1.5 kilowatts, to compensate for a three-fold loss in <br />antenna effectiveness because of height limitations. This <br />increase in power, in turn, increases the possibilities for <br />his signal to overload nearby television and radio <br />receivers, creating interference for viewers and listeners. <br />A high amateur antenna provides a greater degree <br />of immunity from television interference than does a low <br />antenna. The sole source of radiated RF energy from <br />the Amateur Radio station is its antenna. Raising that <br />antenna to an increased height, well above the level of <br />existing antennas for television reception, will reduce the <br />possibility of interference to television reception from <br />fundamental overload.