WO1999052256A1

WO1999052256A1 - Apparatus and method for detecting either a fault or an unauthorized tap in a telephone line

Info

Publication number: WO1999052256A1
Application number: PCT/US1998/006797
Authority: WO
Inventors: Hector M. Vasquez
Original assignee: Donald D. Criss Co. Doing Business As Anti-Wiretap Devices Company
Priority date: 1998-04-06
Filing date: 1998-04-06
Publication date: 1999-10-14
Also published as: AU6952898A

Abstract

An apparatus and method for determining an abnormal condition of a telephone line (16). A tone generator (10) applies a signal having a frequency of at least 20,000 hertz to the telephone line (16) to determine a reference frequency loss under normal conditions. The same tone generator (10) can apply a similar signal to the telephone line (16) to determine an abnormal decibel loss under abnormal conditions using the signal detector (20) and dbm computational device (52). The difference in the decibel loss indicates the abnormal condition of the telephone line (16).

Description

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

This invention relates to means for detecting either fault or an unauthorized tapping of

a telephone line, and more particularly to a method for detecting a change in frequency 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 by earth moving equipment and the like. One of

the problems with such faults is that it is difficult to precisely locate where 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

-1- 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, volts 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 a signal having a

frequency of at least 20,000 hertz. The apparatus also includes second means for determining

a reference decibel loss in the telephone line under normal conditions when said signal is

applied to said telephone lines. The apparatus also includes third means for determining an

abnormal decibel loss in said telephone line caused by said abnormal condition when said

signal is applied to said telephone line. The difference between said reference decibel loss and

said abnormal decibel loss indicates the abnormal condition of said telephone line.

-2- The present invention also provides a method for detecting an abnormal condition of a telephone line, comprising the steps of applying to said telephone line a signal having a

frequency of at least 20,000 hertz, and determining a reference decibel loss in said telephone

line under normal conditions when said signal is applied to said telephone line. The method

also includes the step of determining an abnormal decibel loss in said telephone line caused by said abnormal condition when said signal is applied to said telephone line. The difference

between said reference decibel loss and said abnormal decibel loss 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 either determining the location of a fault in the line, or the presence

of unauthorized equipment connected to the line. For wire tap purposes, the device is

designed to measure frequency changes in working and non-working telephone pairs between a test location and a local switching office. The test apparatus includes a transmitter and a

receiver with a tone selection of 20,000 hertz or greater, with a digital display capability.

Typically, most telephone lines comprise two copper twisted wires. If the user intends to use the equipment for locating a fault in the line he connects the tone generator to the tip and ring lines and transmits a tone of 20,000 hertz or greater. The device has a receiver which monitors

the reflection of the tone frequency and preferably has a digital read out indicating the decibel drop in the tone. For illustrative purposes, the drop in the audible signal may be assumed to measure a 7.0 decibel measurement loss (dbm).

Assuming the normal decibel drop for a telephone line is 7.0 for a particular subscriber, if the subscriber takes a reading which measures 7.3, then the 0.3 added drop is proportional to the distance from the test site to the location of possible fault. Assuming there is a 0.1 loss for every hundred feet, the user can determine the location of the fault at 300 feet.

-3- This would tell the repair crew where to locate the fault in the interrupted telephone line.

Employing unconventionally higher frequencies, that is 20,000 hertz or above gives

a greater dbm loss range, which in turn improves the precision of the device. The use of a frequency lower than 20,000 hertz gives false readings because the frequency is too low.

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 frequency loss measured in terms of the decibel loss. Knowing this he can periodically

test the line to determine if there is either an increase or a reduction in the frequency loss. If somebody is tapping the line, the tapping equipment, because of the added copper wire or

equivalent, will reduce the frequency. If the eavesdropper is using a voltage activated device,

the dbm reading will drop. In addition to the more precise reading of the existence of a tap,

using a frequency of 20,000 hertz or greater transmits a signal 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 invention pertains upon reference to the following detailed

description.

Description of the Drawings

The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which: FIGURE 1 is a system block diagram of a telephone system illustrating how a fault in

the telephone line may be located;

FIGURE 2 is a block diagram of a telephone security tapping detection system

illustrating the invention;

FIGURE 3 is a diagram illustrating how the tone generator attaches to the twisted

-4- copper wires on the telephone line; and

FIGURE 4 is an electrical schematic of a preferred embodiment of the present invention.

Description of the Preferred Embodiment

Referring to Figure 1 , a circuit has been shown in block diagram form. A system tone

generator 10 is connected 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 3, a tone generator 10 is connected to the tip and ring lines 12 14, respectively, which are 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 RMS to DC converter with power supply.

Assuming that in a line several hundred feet long the absence of a dial tone indicates

that a break in the line caused by some means, the user generates a tone into the lines which by virtue of self-inductance causes a drop in the frequency which will be reflected in signal

detector 20. Detector 20 digitizes the signal to produce a dbm reading in a visual device 22. Dbm is a common term used to refer to the decibel loss in the telephone line. The loss is then compared to that of a normal line. If the normal loss has not been determined before the fault occurred, then it may usually be determined by generating a tone in a neighboring line which

-5- does not have a fault.

Assuming the normal loss is 7.0 dbms and the present abnormal condition loss if 7.3

dbm, the difference is 0.3 dbms. The location of the loss, that is the distance from the test site

to the fault in the line, may then be determined by a formula which uses the standard loss per

foot of line. For example, in the same line, a 0.1 dbm loss occurs in a hundred feet of line.

A 0.3 dbm loss then indicates that the fault is 300 feet from the test site. The repair crew can then fairly precisely locate where the repair must be made.

Figure 2 illustrates another application of the invention. In this case, the block diagram

shows a tone generator 10 connected to the tip and ring lines 12 and 14, respectively, of the

telephone loop 16. The signal detector 20 is also connected across the tip and ring lines 12 and

14, respectively, or may be combined in some way with the tone generator 10. Normally there is no unauthorized tapping activity across the line.

The user calculates a base decibel drop across the ring lines by generating a tone in

excess of 20,000 hertz. Assuming that this results in a base line dbm of 7.0, the user either

periodically connects a tone generator 10 and signal detector 20 across the line to determine the instantaneous status of the line, or provides a permanent connection of these devices on the line to provide a continuous status reading. Unauthorized tapping equipment 30 that has

been connected across the tip and ring lines 12 and 14, respectively, will then create a change in the dbm, either an increase or a reduction, depending upon the nature of the tapping

equipment 30.

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 as to provide a continuous monitoring of the status of the line. Upon detecting a predetermined change in the dbm, device 32 can then energize an alarm 34.

-6- In the alternative, computer 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 a 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 4, there is shown an electrical schematic of a preferred

embodiment according to the present invention. The major components are shown enclosed

in phantom lines, such as a tone generator 10, a signal detector 20, a 9-volt power supply 42, a dual RJ 14 female connectors 44 for connection to the telephone loop, an RMS to DC converter 46, and a switching arrangement 48.

It should be noted that the tone generator 10 provides for a tone selection from 32K to

51. IK using a plus 5 volt power source. In addition, the resisters are 1 % tolerance.

In the signal detector 20, there is shown an LCD display, digital panel volt meter 22 which is connected to a potentiometer 49 with a plus 9 volt power supply 42. To the right of

the display 22, there is shown a push button switch 50 for momentary monitoring the phone line. A down regulator voltage converter is also provided to render consistency in

measurement in lesser voltage draw from the battery supply.

It should be noted that a miniature pushbutton switch 1 is provided to the telephone line to prevent foreign circuit noise winding up or down when powering up or turning the apparatus off.

-7- Numerous modifications, variations, and adaptations may be made to the described embodiments without departing from the scope of the invention as defined in the appended claims.

-8-

Claims

1. A method for detecting a discontinuity in a telephone line and the distance of the

discontinuity from a testing device connected to said line, the line comprising of a pair of

twisted wires between the test location and the discontinuity location to fault, said method comprising the steps of:

generating a test tone at a test frequency and applying said test tone to the telephone line at the test location;

measuring the frequency loss in the telephone lines by comparing the reflected frequency to a base frequency;

calculating the distance from the test location to the discontinuity location according

to the formula D equals frequency lost times loss per foot, where D is the distance between the test location and the discontinuity location and the frequency loss is a difference between

the test frequency loss and the actual frequency loss times the loss per foot.

2. A method as defined in claim 1, in which the tone is generated at a frequency in excess of 20,000 hertz.

3. A method as defined by claim 1 , in which the fault is a discontinuity in the telephone

line.

4. A method for detecting the authorized connection to a telephone line comprising the

steps of: generating a test tone at a test frequency and applying the test frequency to the

telephone line;

-9- measuring the frequency loss in the telephone line from the test frequency to establish a base frequency loss;

generating the test tone at the test frequency to the telephone line and comparing the frequency change to the base frequency of the loss.

5. A method as defined in claim 4, including the step of determining if the frequency change reflects a drop or gain with respect to the test frequency loss.

6. A method as defined in claim 4, including the step of calculating the location of the

circuit in which the tone is generated to the location of the unauthorized tapping according to the formula:

D equals FL times frequency loss per foot.

7. A method as defined in claim 4, in which the tone is generated at a frequency of at

least 20,000 hertz.

8. A method as defined in claim 5, in which the telephone line has copper wire and the tone is generated through the copper wire.

9. A method as defined in claim 4, including the step of generating an alarm signal if

the frequency change exceeds a predetermined value.

-10-

10. A method as defined in claim 7, including the step of continuously generating the tone, and monitoring the frequency loss to determine the time of a temporary tapping in the

telephone line.

11. Apparatus for deteimining an abnormal condition of a telephone line, including:

first means for applying to said telephone line a signal having a frequency of at least

20,000 hertz; second means for determining a reference decibel loss in said telephone line under normal conditions when said signal is applied to said telephone line;

third means for determining an abnormal decibel loss to said telephone line caused by

said abnormal conditions when said signal is applied to said telephone line; and a difference between said reference decibel loss and said abnormal decibel loss indicating said abnormal condition of said telephone line.

-11- AMENDED CLAIMS

[recceived by the International Bureau on 30 November 1998 (30.11.98); original claims 2 and 7 cancelled; original claims 1, 4 and 10 amended; remaining claims unchanged (3 pages)]

1. A method for detecting a discontinuity in a telephone line and the distance of the discontinuity from a testing device connected to said line, the line comprising of a pair of twisted wires between the test location and the discontinuity location to fault, said method comprising the steps of: generating a test tone at a test frequency in excess of 20,000 hertz and applying said test tone to the telephone line at the test location; measuring the frequency loss in the telephone lines by comparing the reflected frequency to a base frequency; calculating the distance from the test location to the discontinuity location according to the formula D equals frequency lost times loss per foot, where D is the distance between the test location and the discontinuity location and the frequency loss is a difference between the test frequency loss and the actual frequency loss times the loss per foot.

3. A method as defined by claim 1 , in which the fault is a discontinuity in the telephone line.

4. A method for detecting the authorized connection to a telephone line comprising the steps of: generating a test tone at a test frequency of at least 20,000 hertz and applying the test frequency to the telephone line; measuring the frequency loss in the telephone line from the test frequency to establish a base frequency loss; generating the test tone at the test frequency to the telephone line and comparing the

- 12 - frequency change to the base frequency of the loss.

circuit in which the tone is generated to the location of the unauthorized tapping according to the formula: D equals FL times frequency loss per foot.

9. A method as defined in claim 4, including the step of generating an alarm signal if the frequency change exceeds a predetermined value.

10. A method as defined in claim 4, including the step of continuously generating the

tone, and monitoring the frequency loss to determine the time of a temporary tapping in the

telephone line.

11. Apparatus for determining an abnormal condition of a telephone line, including: first means for applying to said telephone line a signal having a frequency of at least 20,000 hertz; second means for determining a reference decibel loss in said telephone line under normal

- 13 - conditions when said signal is applied to said telephone line;

said abnormal conditions when said signal is applied to said telephone line; and

a difference between said reference decibel loss and said abnormal decibel loss indicating said abnormal condition of said telephone line.

- 14 -