Abstract: A directional concealed object locator, say metal detector, employing a beat frequency oscillator and at least two search oscillators. The search oscillators each include a loop antenna which in part serves to determine the search frequency signal rate of each oscillator and functionally serves to produce an electromagnetic field of relatively large proportions from each loop antenna which is portably so orientable as to have the extended electromagnetic field lines, which emanate from each loop antenna, separately coupled to a buried, or otherwise obscured metal object and thereby produce changes in the search signal rate as the proximity therebetween is varied.

Abstract: Calibration technique comprises the production of a calibration signal hag a single sideband of modulation which is locked to an incoming carrier. The sideband may be on either side of the carrier and is phase adjusted to be amplitude modulated, frequency modulated or a combination of the two modulation forms.

Abstract: A metal locator apparatus the preferred practice of which includes two electromagnetic field radiating inducers, which serve to act upon a metal object deposited in a covert medium from distinctly separate positions, including two separate search oscillators one of which is connected to each of the inducers thereby producing two output signals, each of which include distinctive frequency perturbations introduced by the proximal relationship of the metal object with the responsive inducer. The two signals are then each individually combined, or mixed with a common beat oscillator which action results in two output sets of sum and difference frequencies. By way of suitable filtering, the two difference frequencies come out as distinctly separate audio frequency signals the pitch of which fluctuates in direct accordance with the frequency perturbations appearing on the individual search oscillator combinative signals.

Abstract: 1.

Abstract: A frequency synthesizer, responsive to a reference signal having a frequency f.sub.r, for supplying an output signal at a frequency selectable from M times N signal frequencies (where M and N are preselected integers) is disclosed. In each disclosed arrangement, a set of M signals that are each harmonically related to f.sub.r is derived by a cascade connected harmonic generator and comb filter, and a set of M signals that are each harmonically related to f.sub.r /M is derived from the reference signal by a cascaded frequency divider, harmonic generator and comb filter. Each of these signal frequencies within the two sets of signals can be selectively coupled to the input ports of signal mixing apparatus and bandpass filtering is employed to couple either the mixer sum or difference frequency to the synthesizer output terminal. In some situations, a single mixer circuit and bandpass filter is employed.

Abstract: A frequency synthesizer operating in the quaternary system of numeration and comprising a plurality of "quaternade" units, each including a frequency inserting element with a mixer which receives respective frequencies equal to 63 A, 64 A, 65 A and 66 A, A being a predetermined frequency. The said frequencies are generated from a common standard frequency through dividing the standard frequency by variable ratios generating harmonics of the resulting frequencies and filtering.