With the help of neat diagram, explain the working of phase discriminator.

1 Answer



This discriminator is also known as the center tuned discriminator or the Foster Seeley discriminator after its inventors. It is possible to obtain the same S- Shape response curve from a circuit in which the primary & the secondary winding are both tuned to the center frequency of the incoming signal. This is desirable because it greatly simplifies alignment & also because the process yields far better linearity.

Thus although the individual component voltage will be the same at the diode input at all frequencies, the vector sums will differ with the phase difference

between primary & secondary windings. The result will be that the individual output voltage will be equal only at f.

At all other frequencies the output of one diode will be greater than that of the other. Which diode has the larger output will depend entirely on whether fm is above or below fc. As for the output arrangements, it will be positive or negative according to the input frequency. As required the magnitude of the output will depend on the deviation of the input frequency from fc.

If explanation is given in 3 cases fin = fc, fin > fc + Δf and fin<fc- Δf should be given marks

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