The original circuit diagram was drawn previous to any reference work on the subject; however, in the construction of the system it was found necessary to add to and subtract from the original circuit. For instance, in order to isolate the oscillator from the modulator and to amplify the carrier voltage it was necessary to add buffer amplifier stages; since only one system was built and since the system worked on the tuned detector principle, no filters were deemed necessary. Other circuit changes of minor importance are; the use of individual plate voltage supplies to minimize feedback between stages; the use of regenerative detection; and a variation in the obtaining of the oscillator output. The system works satisfactorily, but is very critical; this is largely due to the fact that regenerative detection is used. Once the system is adjusted for quiet distortionless operation, it is found that an increase in modulating potential sufficient to over modulate the carrier introduces distortion. This is probably due to the fact that the tube is not operating on a parabolic portion of the grid voltage plate current characteristic curve during a large portion of each cycle, thus introducing third order, fourth order, fifth order, and nth order distortion terms.* * It is to be remembered that the plate current can be expressed as a power series of n terms of the grid voltage, i.e. --- [see equation] The number of terms depends upon the portion of the curve over which the tube is operating; thus, for "square-law" or second order modulation, which occurs over the parabolic portion of the characteristic curve, n = 2; for third order modulation, n = 3; etc. / M.S.