An example of a simple liquids machine

While the instrument whose block diagram is shown at right was specifically intended to do 13C Fourier transform NMR at 15.1 MHz in liquid samples, it could be used for a variety of nuclei in liquid and solid samples. It uses a Varian DP-60 magnet, normally operated at 14.1 kG. 

The instrument is built on the heterodyne principle with 10 MHz as the intermediate frequency. Both the lock frequency and the spectrometer frequency are derived from the synthesizer, which ensures that any source frequency drift would appear equally in both the lock and the observe channels thus resulting in maintaining the resonance condition. 

A major benefit of using the heterodyne principle in a spectrometer is the ease of changing frequencies at moderate cost. In this system, the spectrometer frequency can be changed by about a factor of two by simply dialing a new 

The probe uses a single-coil for 20 mm spinning samples at room temperature. There are no tuning elements in the probe -- rather the tuning is by a variable inductor at the end of a A./4 cable as described in the discussion of quarter wave cables in V.C.8. The transformer at the end of the second quarter wave cable matches the impedance between the tank circuit and the broadband preamplifier. The output 

We list the specific components used for operation at 15.1 MHz, without any endorsements, implied or otherwise. 

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