. The Bell System technical journal . onnected as shown in Fig. 13. The principal advantage of this type of modulator or demodulatoris that in the ideal case (and to a lesser degree in the practical case) NEW SINGLE CHANNEL CARRIER TELEPHONE SYSTEM 177 each modulation product appears only in one of the four branches ofthe circuit. For example in the case of the modulator, if a voltage offrequency F is applied to the input and a voltage of frequency Cis applied by the carrier supply circuit, resulting products of modula-tion will appear in the ideal case as shown in Fig. 13. It is obviousthat t
. The Bell System technical journal . onnected as shown in Fig. 13. The principal advantage of this type of modulator or demodulatoris that in the ideal case (and to a lesser degree in the practical case) NEW SINGLE CHANNEL CARRIER TELEPHONE SYSTEM 177 each modulation product appears only in one of the four branches ofthe circuit. For example in the case of the modulator, if a voltage offrequency F is applied to the input and a voltage of frequency Cis applied by the carrier supply circuit, resulting products of modula-tion will appear in the ideal case as shown in Fig. 13. It is obviousthat the only unwanted products in the output which cannot be sup-pressed by filters or balance are those which are of the frequency(C dz AV) which for some values of A and V fall in the frequencyrange of the desired sideband (C + V) or (C — V). These components, however, are normally more than 50 db weakerthan the sideband and are not noticeable. Of course, the term A Vrepresents not only odd harmonics of V but odd order intermodulation. A= ANY ODD INTEGER B= ANY EVEN INTEGER C= FREQUENCY OF APPLIED CARRIER V= FREQUENCY OF INPUT Fig. 13—Simplified schematic of copper oxide modulator. products such as (2Fi± V2). The relative amplitudes of the{C ±: AV) terms increase with load in a similar manner to that forthe distortion products of an ampUfier as the overload point is ap-proached, and the effect on articulation is the same. For the actual case the modulator balance is not perfect and allproducts and the original frequencies do appear in all branches ofthe circuit including the output. However, the balance in most casesis greater than 30 db and the filter requirements are helped to thatextent over some portions of the frequency range. This is particularlyhelpful in connection with suppressing the carrier from the output andinput since it lies only about 200 cycles from the pass band and itwould be costly to obtain all of the suppression required by means offilters. With a singl
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