Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

120 FREQUENCY MODULATION, Volume Icenter meter which indicates zero discriminator current when thereceiver is exactly tuned for FM. Separate gain controls were providedfor the i-f systems and also for the individual audio amplifiers. Thereceiver output circuit was provided with a very sharp 8-kc low-passfilter with a disconnecting key and the high-frequency de-emphasiscircuit at this point was also provided with a disconnecting key. Asingle switch served to select the type of modulation which it wasdesired to receive.Fig. 6Four receivers were specially built by the RCA ManufacturingCompany for this test and would theoretically give full output with anr-f voltage of only 1/10 microvolt across the input terminals.The hisslevel of 1 microvolt peak in these receivers was representative of thebest modern receivers and was produced by thermal agitation in theantenna circuits and by tube hiss. They were made as good as receiverscan be built in order that the final conclusions concerning frequencymodulation as a system would not be erroneous due to apparatusshortcomings. The sacrifice of receiver design to price will not permit