Noise and Spin-noise: Cable dependence of Optimal Tuning/Matching Conditions

TL;DR

This paper investigates how the length of coaxial cables in NMR setups influences optimal tuning, noise characteristics, and sensitivity, revealing cable-dependent effects on reception tuning and spin-noise signals.

Contribution

It demonstrates the cable dependence of optimal tuning conditions and noise line shapes in NMR, providing insights for improved sensitivity and probe optimization.

Findings

Cable length affects reception tuning and noise line shapes.

Optimal tuning conditions vary with cable length.

Cable-dependent effects influence sensitivity enhancements.

Abstract

Previous studies have shown that tuning/matching conditions optimized for transmission and detection can be significantly different for a variety of commercial NMR probes. In addition, it was also shown that by optimizing reception tuning (as opposed to typical transmission or reflection tuning) one may in some cases obtain sensitivity enhancements by as much as 25-50%. In earlier work, spin-noise and absorbed circuit noise signals have also been used to characterize reception optima. In this work, we show how the length of the coaxial transmission line cable between the pre-amplifier and the probe affects the positions of the reception tuning optimum, the radiation damping strength, induced frequency shifts, as well as, the shape of the spin-noise and absorbed circuit noise line shapes.