NQR testing method and apparatus

An apparatus for and method of Nuclear Quadrupole Resonance testing a sample are disclosed. The technique comprises applying excitation to the sample to excite nuclear quadrupole resonance at a plurality of different nuclear quadrupole resonance frequencies, detecting the resonance responses to the excitation at the plurality of frequencies, and processing the resonance responses at the plurality of frequencies to yield a combined response. The combined response may have a signal to noise ratio larger than that of any individual response.