Abstract: The present invention is related to intrusion sensors for alarm systems which employ Doppler detection. The transmitter of this invention transmits pulse modulated signals having a pulse repetition frequency greater than twice the highest Doppler frequency to be detected. In a manner similar to the well known sampling theorem, the received reflected pulses contain all the Doppler information contained in a similar continuous oscillation Doppler detection system because the highest Doppler frequency to be detected can be reconstituted from the received reflected signals. The duty cycle of the transmitted pulses is limited by the above described pulse repetition frequency limitation and a further requirement that the pulse length be sufficient to enable return of the leading edge of the pulse prior to the end of the pulse.

Abstract: A method and apparatus for analyzing a sample comprising gyromagnetic species in which the sample, is placed in a uniform DC polarizing magnetic field and irradiated by an AC magnetic field, at an angle to the DC field, while the DC field is modulated by square wave signal whereby the resultant resonance signal comprises a frequency modulated spectrum centered around the resonance frequency and having sideband components separated by the frequency of the square wave signal and the amplitudes of which are proportional to the difference of two resonance intensities switched by the two extreme intensity values of the DC field. Upon detection of the sidebands by an RF receiver, DC levels, proportional to the intensity of the detected sidebands, are provided, permitting display of the resonance line shape on an oscilloscope.