26 INSTRUMENT THAT IS A NARROW-BAND SWEEPING OSCILLATOR FOR USE WITH AN OSCILLOSCOPE IN DEFINING THE PASS BAND CHARACTERISTICS OF AMPLIFIERS AND FILTERS BY PROVIDING A NARROW FREQUENCY SWEEP WHICH CAN BE CENTERED AT FREQUENCIES FROM 10 TO 200 KILOCYCLES AND DEVELOPS MARKER PIPS WHICH ARE INDEPENDENT OF THE AMPLIFIER CIRCUITS UNDER TEST AND OTHER USES