Review of Scientific Instruments · 1972 · 12 citations · 2 references
Natural SciencesElectrical EngineeringAnalytical ChemistrySpectroscopic AnalysisSpectroscopyAbsorption SpectroscopyMagnetic Resonance Signal FormationMagnetic Resonance SpectroscopyNuclear SpectroscopyRadio SpectroscopyMagnetic Resonance DetectionNuclear Magnetic Resonance SpectroscopyResonanceTunable Circuits
A nuclear magnetic resonance detection system for the vhf-uhf frequency range is described in detail. It consists of a radio frequency bridge built around a coaxial hybrid T. The sample is contained in a tunable L-C resonator coupled with an adjustable impedance transformer to a 50 Ω airline. The system is thus fully tunable over wide ranges of frequency from a remote location. For example, using a two-turn copper ribbon coil, the range 270–710 MHz is covered: The system may be set to any desired point in this range within a few minutes. The system was used with standard lock-in detection to obtain the absorption derivative ∂χ″/∂H. An absolute noise measurement was made at a radio frequency of 300 MHz and an audio detection frequency of 200 Hz. This showed that the root mean square noise at the lock-in output was between four and seven times the value corresponding to the rf Johnson noise at the bridge. The system was used to observe a proton resonance in a Bitter type solenoid at 125 kG.
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