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In their 1946 letter, Felix Bloch, William Webster Hansen, and Martin Packard reported water at room temperature. A steady magnetic field along $z$ and an oscillating field along $x$ produced a signal in a pickup coil along $y$, displayed on an oscilloscope. Some samples included paramagnetic additives to accelerate thermal equilibrium. Resonance fields at two frequencies gave the same field-to-frequency ratio, consistent with the proton value.^[ref]

The detailed paper describes glass water bulbs inside tuned receiving coils. Transmitter coils, shields and a conducting paddle controlled leakage. Field modulation at 60 Hz drove the horizontal oscilloscope sweep. A diode and audio amplification supplied the vertical trace. Vibration changed coupling: their largest difficulty. Coil tuning capacitors formed tank circuits. The actual receiver omitted the conceptual diagram's radiofrequency amplifier.^[ref]

The orthogonal coil axes suppress direct transmitter pickup, but do not eliminate it. A field-dependent signal at the nuclear resonance must be distinguished from leakage and noise; merely detecting a radiofrequency voltage is insufficient. This is why the field sweep and the independently checked field-to-frequency ratio matter.

An experimental physicist who coauthored Felix Bloch's nuclear-induction experiments. Precessing nuclear magnetization generated a radiofrequency signal in a coil surrounding the sample. Detecting the induced signal made collective nuclear motion directly measurable and helped establish bulk nuclear magnetic resonance as a laboratory technique.^[ref]

An experimental physicist who coauthored the Bloch nuclear induction experiment measurements of Felix Bloch and Martin Packard. A sample's precessing nuclear magnetization induces a radiofrequency signal in a pickup coil. Detecting that signal connects the collective motion of nuclear magnetic moments to nuclear magnetic resonance, making the same sample's magnetic dynamics repeatedly observable.^[ref]