. The Bell System technical journal . considerable margin) except for a few sets intended prima-rily for bench use. Figure 3 illustrates the use of lightweight test equipmentin maintaining airborne radars. Environmental Influences Military usage requires that the test equipment be capable of efficientoperation at any ambient temperature between a minimum of the order of-40° to -55° C and a maximum of the order of +65° to +70° C, as wellas at any relative humidity up to 95%. In addition the set must withstandcontinued exposure to driving rain, dust storms and all other conditions en-countered i
. The Bell System technical journal . considerable margin) except for a few sets intended prima-rily for bench use. Figure 3 illustrates the use of lightweight test equipmentin maintaining airborne radars. Environmental Influences Military usage requires that the test equipment be capable of efficientoperation at any ambient temperature between a minimum of the order of-40° to -55° C and a maximum of the order of +65° to +70° C, as wellas at any relative humidity up to 95%. In addition the set must withstandcontinued exposure to driving rain, dust storms and all other conditions en-countered in tropical, desert or arctic climates. Often the test set in its 440 BELL SYSTEM TECHNICAL JOURNAL transit case must be capable of submergence under water without ill with a fungicidal lacquer is a standard requirement. Simplicity, Reliability, Accessibility Not only must the functioning of the test set be reliable, stable and trou-ble-free, but the set must make minimum demands for special skill or tech-. Fig. 3—Portable units used in checking airhoriu radars al Hnca Raton, Fla. nique on the part of the maintenance man. Access for maintenance pur-poses, while important in radar test sets, is not as controlling as in the radarsthemselves and sometimes has to be sacrificed in part for compactness. Ruggedness For general application, the test must be capable of with-standing airplane vibration, the shock of hea\y guns, depth charges and }riCKO]]AVE RADAR TESTING 441 near misses, and the combinations of shock and vibration connoted by therequirement of transportation over all types of terrain in any Army vehi-cle. Test and experience have made it possible to translate these generalrequirements into two specific requirements, namely the ability to withstand(1) vibration at frequencies from 10 to v^3 cycles per second with yg excur-sion for 30 minutes in each of three axes and (2) the shock produced by a 400lb. hammer falling through distance
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