. Bell telephone magazine . is concretebuilding; the radio equipment and power supply are inside, about half-way up. Theairplane warning beacon required on most such towers is visible between the antennas 222 Bell Telephone Magazine WINTER Using Microwave Frequencies The equipment used in the radiorelay system consists of the samebasic elements as are used for otherBell System radio services. Theseinclude radio transmitters, radio re-ceivers, and antennas. The main dif-ferences between the radio relayequipment and that used for the othersystems are the use of microwave fre-quencies, the new te
. Bell telephone magazine . is concretebuilding; the radio equipment and power supply are inside, about half-way up. Theairplane warning beacon required on most such towers is visible between the antennas 222 Bell Telephone Magazine WINTER Using Microwave Frequencies The equipment used in the radiorelay system consists of the samebasic elements as are used for otherBell System radio services. Theseinclude radio transmitters, radio re-ceivers, and antennas. The main dif-ferences between the radio relayequipment and that used for the othersystems are the use of microwave fre-quencies, the new techniques involvedin the apparatus design, and the abil-ity of the equipment to handle widefrequency bands. The functions of the radio equip-ment can be readily understood byfollowing a simplified account of thecourse of a signal passing over thesystem. The signal to be transmitted issuperimposed on the transmitting fre-quency, which lies in the range from3,700 to 4,200 megacycles. Thisradio signal is amplified and then sent. A Bell Telephone Laboratories engineer conducts experi-mental work on a transmitter-modulator unit 0/ radiorelay equipment, shown at the upper right to an antenna, where the energy isconcentrated in a narrow beam di-rected through space toward the firstrepeater station along the the energy is concentrated, it isnot necessary to use the millions ofwatts which would be required if theenergy were scattered in all direc-tions, as in radio broadcasting. In-stead, the actual radio power outputis only half a watt, or about the sameamount of energy required to operatea flashlight bulb. Yet to obtain thepower to provide adequate amplifica-tion and this amount of radio energy,several hundred watts of input poweris required. The relay station receives the rela-tively weak microwave signal, ampli-fies it to make up for the loss it hassuffered in spanning the distance fromthe preceding station, and sends it onto the next station. This process isrepeated over
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