. The Bell System technical journal . ver sensitivity the CW power is first adjusted so that a power of 1milliwatt is delivered to the pad and attenuator. Then with the set in thepulsed condition the amplitude of the test signal is adjusted by means ofthe attenuator and pad until the signal on the radar indicator is barelydiscernible. It is necessary for this test that the frequency of the testsignal be equal to the magnetron frequency. The frequency meter isprovided as part of the signal generator for this purpose. The receiver recovery, the time required by the receiver to recoverafter
. The Bell System technical journal . ver sensitivity the CW power is first adjusted so that a power of 1milliwatt is delivered to the pad and attenuator. Then with the set in thepulsed condition the amplitude of the test signal is adjusted by means ofthe attenuator and pad until the signal on the radar indicator is barelydiscernible. It is necessary for this test that the frequency of the testsignal be equal to the magnetron frequency. The frequency meter isprovided as part of the signal generator for this purpose. The receiver recovery, the time required by the receiver to recoverafter disablement by the transmitter pulse, determines the minimum rangeat which a radar can be used. With this test set the receiver recoverycharacteristic is indicated by the amplitude of the test pulses in the intervalimmediately following the transmitter pulse. The set is also adapted to serve as an FM signal generator. A sawtoothwave applied to the repeller gives a succession of frequency sweeps, each 448 BELL SYSTEM TECHNICAL JOURNAL. t MICROWAVE RADAR TESTING 449 about 20 mc wide, and lasting about 6 microseconds. With this frequencymodulated signal the width of receiver response may be observed on aClass A oscilloscope ( one showing signal amplitude vs. time). However,with non-adjustable IF strips such measurement is seldom required. Failureof the radar AFC to follow frequency changes due to antenna scanning orother causes is indicated by a change in the indicator presentation. Pullingof the magnetron frequency due to changes in load impedance can be de-tected by turning off the AFC. Signal Generator Designs Designs of signal generators developed for the military arms during thewar are interesting as landmarks of progress. The signal generator of theIE30 test set, deliveries of which began in May 1942, delivered pulsed RFsignals in the 10 cm range, using sine wave synchronization. Followingonly three months later was the signal generator of the Army IE57A andNavy LZ test
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