Adjacent channels and the Fourier curse

This paper shows the results of measurements of adjacent channel interference due to wide and narrow band FM, AM, and SSBAM transmitters. A brief analytic discussion is made to illustrate why the expected results are obtained and a functional method of measurement is described. The measured transmitters were of a standard available commercial design except that in some cases filters were added for audio out-off to show the possible improvement in performance due to restriction of audio band pass to the modulator. Results indicated that at 20 K.C., the narrowest spacing common in mobile radio use, there was little difference between the narrow systems of modulation. At closer spacings than 20 K.C. the SSB transmitter showed limitations due to noise. At closer spacings than 20 K.C. the results for FM were obscured by the limitations of the receiver selectivity.