What is the easiest way to demonstrate low magnetic flux NMR on the bench? I'm trying to build my own low fux density bench NMR set-up, and am well-versed in electronics. Continuous Wave is supposed to be the easiest. I see commercial instruments that stimulate elements in the range 200MHz to 1GHz. Yet this is nowhere near the Lamor frequency for any of the heavier elements unless there is a major-league magnetic field present. Do they superimpose an amplitude/frequency modulated sideband at the Lamor frequency to achieve resonance ? 
Also on the receive side I see drawings where say 200MHz is digitized to find the Lamor resonance. So are they looking for sidebands produced by the Lamor resonance. Or will I get better results looking directly with a magnetometer ?
 A: 1GHz is not NMR but ESR (unless you can find a 22T magnet...). I wouldn't try anything else than water for an NMR demonstrator experiment. It's cheap and the proton density is high. I think they are usually adding a little bit of copper sulfate or so as a quencher, but I didn't look into that. 
Your main worry is the magnetic field. I would try to generate a nice homogeneous 0.5-1T field with an iron  yoke and some permanent magnets. That brings your RF electronics into the 20-40MHz range. You can do excitation and measurement with $20 USB-RF synthesizers and receivers that can be bought on Amazon these days, which leaves mostly the design and tuning of the rf coils. Most of the experiments I have done in the past were using saddle coils, but for a setup with a capillary, a simple cylindrical coil will probably do better (it can also be wound easily by hand, while a saddle coil requires a coil form for support). We were almost always tuning with "capacitors" made from RG-58. That's dirt cheap and your "tuning tool" is a pair of wire cutters. 
