The input impedance of rectifier modulators

It is shown how the input impedance of a rectifier modulator of series, shunt or ring type can be calculated, and a large number of cases are tabulated, assuming (a) that the terminating impedances, while being as frequency selective as desired, are nevertheless purely resistive at all modulation-product frequencies where they are not zero or infinite, and(b) that the rectifiers have a square-wave variation of resistance with time. It is clearly shown that in all cases except one (i.e. a ring modulator with constant-resistance load) the input impedance¿defined as the ratio of the input voltage to the input current at the applied signal frequency¿has the peculiar property of being dependent on the nature and magnitude of the signal-source impedance from which it is being measured.