Surveillance device detection utilizing non-linear junction detection and reflectometry

Abstract

A method and apparatus for detecting concealed surveillance devices coupled to a transmission line uses either a time domain or frequency domain reflectometry operation to locate any impedance anomalies on the transmission line and a non-linear junction detection operation to classify the located impedance anomalies as semiconductor or non-semiconductor based anomalies. The reflectometry operation utilizes the reflection of a test signal to determine the distance to any reflecting impedance anomalies on the transmission line that may be indicative of an electronic device being coupled to the transmission line. The non-linear junction detection operation then compares the amplitudes of re-radiated second and third harmonics of a transmitted fundamental frequency signal to determine if the reflecting impedance anomalies are the result of a semiconductor based non-linear junction. A DC bias voltage and a balanced load may be added to the transmission line to enhance the line's response to the test signals. Any unidentified semiconductor based anomalies are manually inspected to determine if they represent convert surveillance devices.

1 . A method of analyzing a transmission line, said method comprising: 
 performing a reflectometry operation on a transmission line to locate any impedance anomalies on said transmission line; and    performing a non-linear junction device detection operation on said transmission line to classify any located impedance anomalies as semiconductor or non-semiconductor based.    
   
   
       2 . The method of  claim 1  wherein the reflectometry operation is based on time domain reflectometry technology.  
   
   
       3 . The method of  claim 1  wherein the reflectometry operation is based on frequency domain reflectometry technology.  
   
   
       4 . The method of  claim 1  wherein a resistive load is added to said transmission line to improve the sensitivity of the reflectometry operation.  
   
   
       5 . The method of  claim 1  wherein a DC bias voltage is applied to said transmission line and said transmission line is disconnected from its normal operating circuitry to enhance or alter the transmission line's response to either the reflectometry or the non-linear junction detection operations.  
   
   
       6 . The method of  claim 5  wherein the DC bias voltage level is changed in amplitude and/or polarity to evaluate variations between the reflectometry or non-linear junction detection operation measurements at different DC bias voltage levels.  
   
   
       7 . The method of  claim 1  wherein, if no known electronic devices are coupled to said transmission line, said non-linear junction detection operation is performed prior to said reflectometry operation to determine if said reflectometry operation is needed.  
   
   
       8 . The method of  claim 1  wherein performing a non-linear junction detection operation further comprises coupling a fundamental frequency signal to said transmission line and monitoring said transmission line's response to said fundamental frequency signal to determine if any signals are present on said transmission line at harmonic frequencies of said fundamental signal.  
   
   
       9 . The method of  claim 8  further comprising comparing a signal strength at a second harmonic frequency of said fundamental signal to a signal strength at a third harmonic frequency of said fundamental signal to determine if a semiconductor based impedance anomaly is reradiating said harmonic signals.  
   
   
       10 . The method of  claim 1  wherein said non-linear junction detection operation is accomplished using a signal utilized by said reflectometry operation.  
   
   
       11 . The method of  claim 1  wherein said reflectometry operation provides information regarding the reactive nature of said impedance anomaly with regard to capacitance, inductance, and/or resistance.  
   
   
       12 . The method of  claim 1  wherein a single graph is produced that displays the results of both the non-linear junction device detection operation and the reflectometry operation such that impedance anomalies associated with electronic devices are identified by such graph.