Towards optimal noise properties of NMR antenna-receiver chain

A role of a small loop antenna, that acts as a probe in standard NMR systems, is reviewed. It is shown that the noise properties of a whole system are not always dictated just by proper resonant matching of the antenna and the use of high-quality pre-amplifier (as it is usually believed). Actually, the losses and mismatch of all other passive components may have a serious impact on the overall chain sensitivity. A simple theoretical and experimental investigation has shown that careful design of the NMR antenna-receiver chain can substantially decrease the overall noise figure, and therefore increase the system sensitivity.