WO2002028065A1

WO2002028065A1 - Apparatus and method for detecting either a fault or an unauthorized tap in a telephone line

Info

Publication number: WO2002028065A1
Application number: PCT/US2001/029795
Authority: WO
Inventors: Stephen J. Newton
Original assignee: Line Detective Company
Priority date: 2000-09-25
Filing date: 2001-09-25
Publication date: 2002-04-04
Also published as: AU2001294657A1

Abstract

An apparatus and method for determining an abnormal condition of a telephone line. A tone generator (10) applies a signal having a frequency of least 20,000 hertz to the telephone line (12, 14) to determine a reference test signal amplitude under normal conditions. The same tone generator (10) can apply a similar signal to the telephone line (12, 14) to determine an abnormal test signal amplitude under abnormal conditions. The difference in the test signal amplitudes indicates the abnormal condition of the telephone line (12, 14).

Description

APPARATUS AND METHOD FOR DETECTING EITHER A FAULT OR AN UNAUTHORIZED TAP IN A TELEPHONE LINE

The present invention relates generally to an apparatus and a method for detecting either a fault or an unauthorized tapping of atelephone line. More particularly, the present invention relates to an apparatus and a method for detecting a change in the amplitude of a tone generated over the telephone line caused either by a discontinuity in the line or an unauthorized tapping. Telephone lines frequently experience faults which may be caused by a variety of sources, such as a buried line being severed, for example, by earthrmoving equipment and the like. One of the problems with such faults is that it is difficult to precisely determine where and when the fault has occurred. For example, if the line is buried underground, and conventional equipment determines that there is a problem some place along several hundred feet of line, the line repairman has the difficult job of pinpointing the precise location of the discontinuity. If the line is above ground, he may have to progressively climb a series of telephone poles before be can pinpoint the problem. If it is buried, the problem is compounded.

Another problem with telephone lines is the concern for unauthorized telephone line tapping, whether legal or illegal. Some tap detection devices are known in the prior art. See, for example, United States

Patent No.4,634,813 issued January 6, 1987 to Robert P. Hensley for "Wire Tap Detection Device" ;

United States Patent No. 5, 142,560 issued August 25, 1992 to Mark J. Neer for "Wiretap Detector and Telephone Loop Monitor"; United States Patent No.4,680,783 issued July 14, 1987 to Eduard F. B. Boeckmann for "Telephone Security Violation Detection Device"; United States Patent No. 5,287,404 issued February 15, 1994 to David A. Pepper et al. for "Telephone Subscriber Line

Voltage Change Detection"; United States Patent No. 4,760,592 issued July 26, 1988 to Robert P, Hensley for "Wire Tap Detection Device with Passive Testing"; and United States Patent No. 5,099,515 issued March 24, 1992 to Osamu Kobayashi et al. for "Secrecy Device for Wiretapping Prevention and Detection".

These devices are connected to a telephone line for measuring the values of polarity and electrical characteristics of the telephone line, and commonly apply a signal having a frequency in the range of 4,000 to 5,000 hertz. This frequency range is commonly used because it is the range in which most telephone equipment or tapping devices operate.

Such detection devices generally are inaccurate. When a tone generator is used for detecting wire taps in this frequency range, the loss in frequency is such that the device is unable to detect any meaningful signal representing an unauthorized tap.

It is a desideratum of the present invention to avoid the animadversions of the prior art.

SUMMARY OF THE INVENTION The term "abnormal condition" as used herein means a discontinuity in a telephone line, the presence of unauthorized equipment connected to the telephone line, line transmitters, i.e., bugs placed inside the telephone or on the line, extension line eavesdroppers, all voltage activated devices, automatic telephone tape recording devices, faults in the telephone system, etc.

The present invention provides an apparatus for detecting an abnormal condition of a telephone line, comprising first means for applying to the telephone line an exciting signal having a frequency of at least 20,000 hertz.

The apparatus also includes second means for determining a reference amplitude of the exciting signal under normal conditions when said exciting signal is applied to said telephone line.

The apparatus also includes third means for determining an abnormal amplitude of the exciting signal caused by said abnormal condition when said exciting signal is applied to said telephone line.

The difference between said reference signal amplitude and said abnormal signal amplitude indicates the abnormal condition of said telephone line.

The present invention also provides a method for detecting an abnormal condition of a telephone line, comprising the step of applying to said telephone line an exciting signal having a frequency of at least 20,000 hertz, and determining a reference amplitude of said exciting signal under normal conditions when said exciting signal is applied to said telephone line.

The method also includes the step of determining an abnormal amplitude of said exciting signal caused by said abnormal condition when said exciting signal is applied to said telephone line. The difference between said reference signal amplitude and said abnormal signal amplitude

indicating said abnormal condition of said telephone line.

The broad purpose of the present invention is to provide an apparatus and a method for testing a telephone line for the presence of unauthorized equipment connected to the line. For wire tap purposes, the device is designed to measure amplitude changes in working and non-working telephone pairs between a test location and a local switching office. The test apparatus includes a tone generator and a signal detector with a tone selection of 20,000 hertz or greater, with a digital

display capability.

For purposes of determining the existence of a telephone tap on a telephone line, the user initially applies a test tone to the line at 20,000 hertz or greater to determine a base or normal signal amplitude. Knowing this, he can periodically test the line to determine if there is either an increase or a reduction in the amplitude of the test signal. If somebody is tapping the line, the impedance of the tapping equipment in parallel with the line impedance, will reduce the amplitude of the applied test signal. In addition to the more precise reading of the existence of a tap, using a frequency of 20,000 hertz or greater excites the line at a frequency that cannot be detected by the equipment normally used by an unauthorized tapping agency, whether legal or illegal.

Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the present invention pertains upon reference to the following detailed description and accompanying drawings. Description of the Drawings

FIGURE 1 is a block diagram of a telephone security tapping detection system illustrating the present invention;

FIGURE 2 is a diagram illustrating how the tone generator of the present invention is electrically connected to the twisted copper wires of the telephone line; and FIGURE 3 is an electrical schematic of a preferred embodiment of the present invention.

Detailed Description of a Preferred Embodiment of the Present Invention The following detailed description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views.

Referring to FIGURE 1, a circuit has been illustrated in block diagram form. A system tone generator 10 is connected preferably, but not necessarily, between a tip line

12 and a ring line 14 of a telephone loop 16. The connection of the tone generator 10 may be in any suitable location in the circuit, either at the telephone or with the telephone disconnected.

The device may be a feature of a single line telephone, multiple link telephones and any telephones being served by a KSU or a phone switch. It can also be a feature in the connecting

block for either desk or wall phones.

The tone generator 10 must generate a tone with a frequency of at least 20,000 hertz. Frequencies in the range of 5,000 to 10,000 hertz, commonly used in telephone system equipment, will not produce an accurate signal and in many cases produces no signal at all.

Referring to FIGURE 2, the tone generator 10 is shown connected to the tip and ring lines 12 and 14, respectively, which preferably, but not necessarily, may be copper wires twisted together as illustrated. However, to be more precise, the apparatus 40 comprises a tone generator 10, a signal detector 20, and a power supply.

The signal detector 20 preferably, but not necessarily, may also be connected across the tip and ring lines 12 and 14, respectively, or may be combined in some other suitable fashion with the tone generator 10.

Normally there is no unauthorized tapping activity across the telephone line.

The user measures a base or reference signal amplitude across the ring lines by generating a tone which may preferably, but not necessarily, be in excess of 20,000 hertz. The user, then either periodically connects the tone generator 10 and the signal detector 20 across the telephone line to determine the instantaneous status of the telephone line, or provides a permanent connection of these devices on the telephone line to provide a continuous status reading,

Unauthorized tapping equipment 30 which may have been surreptitiously connected across the tip and ring lines 12 and 14, respectively, will then create a change in the exciting signal amplitude, either an increase or a reduction, depending upon the nature of the tapping equipment

30 being used.

The user upon noticing the change can then take corrective steps. The user can employ a computer device 32 which is so connected to the signal detector 20 so as to provide a continuous monitoring of the status of the telephone line. Upon detecting a predetermined change in the

exciting signal amplitude, the computer device 32 can then preferably, but not necessarily, energize

an alarm 34.

In the alternative, or in addition thereto, the computer device 32 could be connected to a form of a printing device 36 which could then determine the time the unauthorized tapping equipment was installed and/or removed from the line. A printout 38 could then be employed to signal the necessity to take corrective steps.

In summary, employing the tone generator 10 that uses a frequency of 20,000 hertz or greater provides a more accurate reading than existing commercially available devices, and in addition is not detectable with current commercially available tapping equipment. Thus, if some agency should be tapping a user's telephone line, the agency would not be aware that the inventive system is being employed for detecting the unauthorized tapping.

With reference to FIGURE 3, there is shown an electrical schematic of a preferred embodiment according to the present invention.

The major components are illustrated enclosed inphantom lines, such as the tone generator 10, the signal detector 20 which may include a rectifier and filter, a power supply 42, dual RJ 14 female connectors 44 for connection to the telephone loop 16, and a switching arrangement 48.

It should be noted that the tone generator 10 preferably, but not necessarily, provides for a

tone selection from 32K to 51. IK using a suitable power source. In addition, the resistors are

preferably, but not necessarily, 1% tolerance. In the signal detector 20, there is shown an LCD display digital panel voltmeter 22 which is preferably, but not necessarily, connected to a potentiometer 49 with the suitable power supply 42. To the right of the display 22, there is shown a push button switch 50 for momentarily monitoring the telephone line. A down regulator voltage converter may also preferably, but not necessarily, be provided to render consistency in measurement in lesser voltage draw from the

battery supply.

It should also be noted that a miniature pushbutton switch 51 is provided to the telephone line to prevent foreign circuit noise winding up or down when powering up or turning off the apparatus of the present invention.

While in the foregoing specification the present invention has been described in relation to this particular preferred embodiment thereof, and many details have been set forth for the purpose of illustration, it will be apparent to those persons skilled in this particular area of technology that the present invention is susceptible of a plethora of additional embodiments and that certain details described hereinabove can be varied considerably without departing from the basic principles of the present invention.

Numerous modifications, variations, and adaptations may be made to the described

preferred embodiment without departing from the scope of the present invention as defined in the appended claims.

Claims

L A method for detecting an unauthorized connection to a telephone line, comprising the steps of:

generating a test tone at a test frequency and applying said test frequency to said telephone line; measuring the amplitude of said test tone when connected to said telephone line to establish a reference test tone amplitude; and generating said test tone at said test frequency to said telephone line and comparing the test tone amplitude change to said reference test tone amplitude.

2. A method as defined in claim 1, including the step of: determining if said test tone amplitude change reflects an increase or a decrease with respect to said reference test tone amplitude.

3. A method as defined in claim 1, wherein: said test tone is generated at a frequency of at least 20,000 hertz.

4. A method as defined in claim 2, wherein:

said test tone is generated at a frequency of at least 20,000 hertz.

5. A method as defined in claim 1, in which: said telephone line has copper wire and said test tone is generated through said copper wire.

6. A method as defined in claim 1, including the step of: generating an alarm signal if said test tone amplitude change exceeds a predetermined value.

7. A method as defined in claim 2, including the step of:

generating an alarm signal if said test tone amplitude change exceeds a predetermined value,

8. A method as defined in claim 1, including the steps of: continuously generating said test tone; and monitoring said test tone amplitude change to determine the time of a temporary unauthorized connection to said telephone line.

9. A method as defined in claim 3, including the steps of: continuously generating said test tone; and monitoring said test tone amplitude change to determine the time of a temporary unauthorized connection to said telephone line.

10. An apparatus for determining an abnormal condition of a telephone line, comprising: first means for applying to said telephone line an exciting test signal having a frequency of at least 20,000 hertz; second means for determining a reference test signal amplitude under normal conditions when said exciting test signal is applied to said telephone line; third means for determining an abnormal test signal amplitude caused by said abnormal condition when said exciting test signal is applied to said telephone line; and a difference between said reference signal amplitude and said abnormal signal amplitude indicating said abnormal condition of said telephone line^*.