Noncontact signal analyzer

A method for detecting the signal waveforms of analog and digital signals transmitted individually and, alternately, in combination, in designated transmission frequency bands on a pair of conductors, comprising:

• coupling, with capacitive means, a sample signal of the transmitted signals from a conductor to a termination impedance;
• conditioning the sample signal at the termination impedance to provide an equivalent sample signal in the form of a low source impedance signal;
• filtering the equivalent sample signal with a plurality of alternate bandpass frequency filters, each alternate bandpass being selected to pass equivalent sample signal frequencies in a different one of the designated transmission frequency bands, and to reject all other signal frequencies;
• detecting the presence of a designated transmission frequency band signal passed by a filter;
• and
• activating an annunciator to notify a user of the presence of a passed transmission frequency band signal.

Apparatus, for detecting the signal waveforms of analog and digital signals transmitted individually and, alternately, in combination, in designated transmission frequency bands on a pair of conductors, comprising:

• a housing, having an axially extending main body portion and a probe portion arranged in tandem therewith, said probe portion being adapted for placement by a user in proximity to the signal conductors, said housing further having a surface area adapted for mounting signal annunciators,
• a substrate, adapted to be removably mounted within said housing, said substrate having mutually opposed major surfaces adapted to fit within said probe portion and said main body portion, said major surfaces being further adapted to receive thereon, in a surface mounted configuration, the components elements of:
• a probe, having first and second plates disposed on opposite ones of said of mutually opposed major surfaces of said substrate, and each connected to an associated termination impedance, each said conductive plate having an associated electrically conductive shield disposed in spaced relationship therewith on said accompanying substrate major surface, said conductive plates being adapted to capacitively couple first and second signal samples of the transmitted signals in each designated transmission frequency band to said associated termination impedance in response to placement of said housing probe portion in proximity to the signal conductors;
• and
• signal conditioning circuitry, including first and second buffer amplifiers responsive, respectively, to said first and second sample signals for providing first and second equivalent sample signals thereof at an output of each amplifier, each said equivalent sample signal having equal signal polarity and substantially equal signal magnitude as its related sample signal, said buffer amplifiers each providing said equivalent sample signal to the commonly associated one of said electrically conductive shields, whereby the voltage signal potential of the conductive shield is substantially equal to the voltage signal potential of its associated plate, said signal conditioning circuitry further including a differential signal amplifier having first and second signal inputs responsive to said first and second equivalent sample signals, respectively, for providing a differential sample signal proportional to the difference sum therebetween;
• wherein said substrate includes conductive material traces disposed thereon to provide signal interconnection between each said conductive plate and its associated termination resistor and buffer amplifier, and wherein the periphery of said conductive plates and the conductive material trace signal connection between each plate and its termination resistor and buffer amplifier are bounded by a co-planar trace shield having an applied voltage potential which is substantially the same as the signal voltage potential of said conductive plates, as necessary, to minimize current leakage across said substrate major surfaces, between said conductive plates and interconnecting signal traces, and other substrate mounted apparatus;
• and
• a signal analyzer, for receiving said equivalent sample signal at each of one or more frequency filters, each said frequency filter having a passband which passes equivalent sample signal frequencies in one of the designated transmission frequency bands and rejects all other signal frequencies, said signal analyzer further including one or more signal annunciators associated with each said frequency filter, said signal annunciators indicating the presence of a designated transmission frequency band signal passed by its associated frequency filter.