Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

&62 FREQUENCY MODULATION, Volume Inot obtainable until the signal is strong enough to reach the thresholdof the wider system.In order to determine the actual difference in signal readabilityfor systems using different frequency deviations, a listening test wasconducted on the two frequency-modulation systems which were usedfor Figures 1 and 2. A 5-kilocycle low-pass filter was inserted in theaudio output of both receivers so that one had a deviation ratio of 1.2and the other 4.The noise consisted of the thermal agitation and tubehiss originating in the radio-frequency circuits.The curves of Figure 4 show the results of the listening tests.—Readability numbers of the amateur RST system are plotted>-against