Two new phenomena, (i) the considerable dependence of the one-port equivalent impedance, represented by an injection-locked self-oscillating system at the locking frequency (within the locking bandwidth), on the external low-frequency signals and (ii) the frequency conversion with a lower-sideband signal gain and an upper-sideband signal suppression using injection-locked oscillator are examined. The paper shows that the manifestation mechanism of such phenomena is parameteric. The explanation lies in the reversibility of the modulation-parametric interactions in perturbing nonlinear self-oscillating systems and in the influence of the second harmonic of the time-varying injection-locked oscillator impedance. An original method of investigation for modulating-parametric and conversion phenomena in perturbing nonlinear self-oscillating systems has been developed, based on the perturbation theory and the method of Samoylo and Spasov. The analytically and experimentally established relations between the components of the low-frequency impedance and the transmission impedance of frequency conversion of a negative-resistance injection-locked oscillator and the locking frequency have been derived.