Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

462 FREQUENCY MODULATION, Volume Iduce faithfully the sounds engraved on a disk. 4 The most importantof these measurements is the frequency response of the head aftercompensation. This type of measurement is made in several ways. Oneof the best-known and widely used direct methods is by the lightDISCRIMINATOR COILS STYLUS(frT GROUND POTENTIAL)Pig. 9—Arrangement of the FM calibrator adapted to a recorder head.pattern. As is generally known, this method consists of recordingseveral frequencies on a disk and comparing their amplitudes with theaid of reflection of light. This method is fairly accurate when certainprecautions are taken and is really a true indication of the performance"*-»?Fig. 10—Push-pull FM plate assembly.of the head, since the head is actually engaged in cutting a disk thatrepresents the normal load on the stylus.Another method which has been widely used consists in measuringthe amplitude of the stylus vibrating freely in air by means of a microscopewhich has been precalibrated to measure small distances. In this