Automatic tuning apparatus and method for substance detection using nuclear quadrupole resonance and nuclear magnetic resonance

Apparatus for tuning a system for detecting a target substance through the use of nuclear quadrupole resonance (NQR) or nuclear magnetic resonance (NMR). The apparatus tunes an RF coil (34) which is employed to excite the substance under test. The tuning apparatus (36) includes a series of fixed value capacitors (93) switched in the tuning circuit by controllable switches (94). A programmable controller (21) is employed to control the switching and thereby the tuning of the coil.