Agilent 1950-08 free download

File name 1950-08.pdf

HEWLETT' PACKARD ft ; f T E C H N I C A L I N F O R M JOURNAL A T I O N F R O M T H E - d p - L A B O R A T O R I E S VOL. 1 No. 12 PUBLISHED BY THE HEWLETT-PACKARD COMPANY, 395 PAGE MILL ROAD, PALO ALTO, CALIFORNIA AUGUST, 1950 A New Monitor for FM Communications Services IN recent years the use of radio communica single FM (or PM) transmission, while the tions has grown enormously in fields such Model 337B monitors up to four transmis as land transportation, public safety, and sions. The latter instrument is similar to the public utilities. The consequent crowding of Model 337A except for a panel switch that available spectrum has resulted in FCC connects any one of the four carrier frequen adoption of tighter carrier frequency toler cies to the monitoring circuits. All coil ances for these radio services. At present changes are performed automatically by the such services are, in general, required to panel switch and no plug-in coils are used. maintain their carrier frequencies accurate The heart of these new monitors is the within 0.01% when below 50 me and within pulse-counter type discriminator which was 0.005% when above 50 me. In addition, developed for the popular -hp- Model 335B periodic measurements must be made to de