Signal to noise ratio studies of PIM and PIM-FM systems†

For a PIM system, wherein the total noise power is the contribution due to d.c. and harmonic powers, an expression for signal to channel noise ratio has been established and it is shown that such a system is superior to an equivalent FM system by 1.6 dB for a bandwidth of 45 KHZ. Consequently a PIM-FM system is studied and this study reveals that it is bettor than an equivalent FM-FM system by 7 dB for a first-stage bandwidth of 45 KHZ. A generalized curve of d.c. noise power valid for the frequency range of 45 to 100 KHZ (applicable to RWM, PLM, PPM and PIM) has been drawn and the total noise power in PIM as a function of channel bandwidth is plotted alongside. The frequency spectrum of PIM-FM signals is analysed and the number of frequency components is 1134. A table has been developed (not given here), with the help of which it is possible to determine the amplitude of any desired frequency component.