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Analytical model for the optimization of the signal-to-noise (S/N) performance for the receiverwith input resonance circuit and variable feedback is developed. It is shown that by varyingthe feedback type and depth optimization of the receiver the best S/N performance could be achieved.This approach is based upon a resonator-receiver model with lumped elements. These assumptionsare relatively general for the model to be applicable for the design of both continuous and pulsereceivers in radio-frequency and microwave bands. The overall S/N performance of the receiver uponthe noise properties of its elements and the feedback settings in the input amplifier is studied fordifferent parameter settings. It is shown that the separate optimization of individual elements doesnot necessarily lead to the best S/N performance of the receiver, especially when bandwidth propertiesand noise contribution of the elements are substantially different. It is shown that critical couplingof the amplifier to the resonance structure could be far from optimum. In some cases the optimumS/N performance could be achieved with the coupling settings less than critical. But under the assumptionsmade the coupling over the critical value does not correspond to the best receiver S/Nperformance. Suggestions on the optimum architecture of magnetic resonance spectrometer receiverswith variable feedback are made.

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