Abstract:
A method and apparatus for testing telephone equipment for longitudinal balance. A signal generating circuit places a test signal at a certain frequency on the tip and ring wires of a telephone line. The telephone line is monitored and the signals on the tip and ring wires are measured and compared against each other. The frequency is gradually increased in set increments until the test frequency is in the megahertz range.

Description:
BACKGROUND 
     A) Field of Invention 
     The present invention relates to communications testing equipment and more particularly to communication testing equipment which tests the longitudinal balance of telephone equipment. 
     B) Background of Invention 
     A telephone line generally contains three separate wires. Two of these wires are referred to as the tip and ring wires and the third wire is usually a grounded wire. The actual signal used in telecommunications is carried on the tip and ring wires with the grounded wire being used as a reference. 
     In the telephone line, the tip and ring wires are continually twisted around one another. Since the telephone line can extend great distances, it can be subject to many disturbances that can cause interference with the electrical signals carried along those lines. By twisting the two wires around each other, it increases the probability of having any disturbances affect both wires equally. This equal distribution of the interference among the two wires reduces the problems caused by any disturbance. 
     Twisting the tip and ring wires around each other is one attempt of ensuring that the two wires are electrically balanced. An imbalance between the wires increases the susceptibility of noise pick-up that can disrupt the transmission of the signals. Accordingly, it is important to be able to test the wires to determine whether they are equally affected by any disturbances in the wire or whether the wires are imbalanced. In testing the wires, it is important that the test equipment itself does not contribute to the imbalance measurement. 
     In the prior art, a telephone line is tested for an imbalance by applying a 1 kHz pulse test signal to both the tip and ring wires. By exciting both the tip and ring wires with the same voltage at the same frequency, the line can be monitored to determine whether an imbalance occurs. If the signal on one wire is different from the signal on the other wire, then an imbalance between the wires exists. This prior art is primarily applicable for voice band application. 
     In applying a 1 kHz test signal, the balance test will return a single measurement representing the balance level between the two wires. If this measurement is below a predetermined level, then the line can be considered to be electrically balanced. The level is empirically determined and approximates the acceptable tolerances of the telephone line. 
     This test, however, does not adequately predict the vulnerability of the line to be potentially disturbed by noise disruptions. By using only one measurement and comparing it against an empirically set standard, it gives an inaccurate depiction of the balance of the telephone line because it oversimplifies the range of different types of disturbances that can affect the line. For example, disturbances at higher frequencies will not be measured by this 1 kHz test. In addition, this inaccuracy does not address the situation when a disturbance is intermittent and the magnitude of the disturbance varies throughout the day above the audio range. 
     A typical voice transmission in a telephone line can have frequencies which range up to 4 kHz. Advances in telecommunications have created the need for transmissions at higher frequencies. For example, an XDSL line can operate in the megahertz range. The conventional method of using a 1 kHz pulse to test for imbalances cannot detect when a disturbance in a line is occurring at such high frequencies. In particular, radio waves which operate at those higher frequency ranges can disturb the high frequency signals sent on the telephone line. In addition, the reach and nature of radio waves can vary during the day which makes radio wave interference to be intermittent. 
     Therefore, there currently exists a need for a balance test to be able to detect imbalances at high frequencies. There also exists a need for a balance test that reports results that more accurately indicate the telephone line&#39;s vulnerability to disturbances due to imbalances in the line. 
     SUMMARY OF THE INVENTION 
     The current invention involves a wide band spectral balance test. The test initiates a signal on the tip and ring wires of a telephone line that starts with a low frequency tone and increases the frequency in predetermined intervals up to the higher frequency ranges. The line is monitored for the signals carried on both the tip and ring. The signals on both the tip and ring wires are measured and compared. Measurements and comparisons of those measurements are taken at each frequency level. The results are then plotted on a graph indicating the decibels versus frequency. 
     In accordance with one embodiment of the invention, a wide band spectral tester comprises a signal generator to create a signal at a set frequency and to cause the created signal to be placed on a first wire and a second wire in a telephone line; and a signal receiver to monitor the first and second wires and compare the signals on the first wire against the signals on the second wire to determine whether the first wire and the second wire are balanced; wherein, the signal placed on the first wire is identical to the signal placed on the second wire and the signal placed on the first and second wires includes signals above 1 kHz. 
     In accordance with another aspect of this embodiment of the invention, the longitudinal balance tester includes a digital signal processor and a digital to analog converter. 
     In accordance with another aspect of this embodiment of the invention, the longitudinal balance tester includes a numerically controlled oscillator. 
     In accordance with another aspect of this embodiment of the invention, the longitudinal balance tester includes a digital signal processor, a differential amplifier and an analog to digital converter. 
     In accordance with another aspect of this embodiment of the invention, the signal generator places the created signal on a grounded wire in the telephone line. 
     In accordance with another aspect of this embodiment of the invention, the signal receiver includes balanced test wires to connect to the first and second wires in the telephone line. 
     In accordance with another aspect of this embodiment of the invention, the first and second wires constitute a twisted pair of wires in the telephone line. 
     In accordance with another aspect of this embodiment of the invention, the created signal includes frequencies above 10 kilohertz. 
     In accordance with another aspect of this embodiment of the invention, the created signal includes frequencies above 50 kilohertz. 
     In accordance with another aspect of this embodiment of the invention, the created signal includes frequencies above 100 kilohertz. 
     In accordance with another aspect of this embodiment of the invention, the created signal include frequencies above 1 megahertz. 
     In accordance with yet another embodiment of the invention, a method for testing a telephone line for longitudinal balance is disclosed which comprises the steps of creating a signal at a set frequency; the signal including frequencies in the megahertz range; placing the signal on a first and second wire in a telephone line; monitoring and detecting signals on the first and second wires; and measuring any differences between signals on the first and second wires. 
     In accordance with another aspect of this embodiment of the invention, the signal includes frequencies above 10 kHz. 
     In accordance with another aspect of this embodiment of the invention, the signal includes frequencies above 50 kHz. 
     In accordance with another aspect of this embodiment of the invention, the signal includes frequencies above 100 kilohertz. 
     In accordance with another aspect of this embodiment of the invention, the signal includes frequencies above 1 megahertz. 
     In accordance with still another embodiment of the invention, a method for testing a telephone line for longitudinal balance is disclosed that comprises the steps of setting an initial frequency; generating a signal at a frequency; causing the generated signal to be placed on a first and second wires in a telephone line; monitoring signals on the first and second wires; measuring any differences between signals on the first wire and signals on the second wire; recording each measurement of differences for the frequency; increasing the frequency level by a predetermined amount; and repeating the generating, causing, monitoring, measuring, recording and increasing steps until the frequency level reaches a predetermined final frequency level. 
     In accordance with another aspect of this embodiment of the invention, the method further comprises step of displaying the difference measurements against the frequency in graphical form. 
     In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than the initial frequency level by 10 kilohertz. 
     In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than the initial frequency level by 100 kHz In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than the initial frequency level by 1 MHz. 
     In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than 10 kHz. 
     In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than 100 kHz. 
     In accordance with another aspect of this embodiment of the invention, the predetermined final frequency level is greater than 1 mHz. 
     In accordance with still another embodiment of the invention, a method for testing a telephone line for longitudinal balance is disclosed that comprises the steps of setting a frequency range to be tested; generating a test signal; said signal including a plurality of frequencies; causing said generated signal to be placed on first and second wires in a telephone line; monitoring signals on said first and second wires; measuring any differences between signals on said first wire and signals on said second wire; recording each measurement of difference for each said frequency that was included in said signal; changing the frequencies that are included in said signal; repeating said generating, causing, monitoring, measuring, recording and changing steps until each frequency in said frequency range has been included in said test signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide an understanding of the invention and constitute a part of the specification. 
     FIG. 1 is a pictorial representation of one embodiment of the present invention. 
     FIG. 2 is a schematic illustrating one embodiment of the signal generating circuit developed in accordance with the present invention. 
     FIG. 3 is a schematic illustrating another embodiment of the signal generating circuit development in accordance with the present invention. 
     FIG. 4 is a schematic illustrating one embodiment of the signal receiving circuit developed in accordance with the present invention. 
     FIG. 5 is a flow chart that shows one embodiment of the present invention. 
     FIG. 6 is a chart that contains the results of three imbalance tests performed in accordance with the present invention. 
     FIG. 7 is a graph that depicts the results of the three imbalance tests performed in accordance with the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a pictorial representation of a longitudinal balance testing unit developed in accordance with the present invention. The longitudinal balance testing unit  10  utilizes three test leads  12 ,  14  and  16  to physically connect to the tip  18 , ring  20  and ground  22  wires in a telephone line  24 . Testing unit  10  includes a processing unit  26  such as a computer that is able to process and analyze the test results. Testing unit  10  also includes testing circuit  27  which administers the test signals on the telephone line  24  and reads the resulting signals on the telephone line  24 . 
     Testing circuit  27  includes a signal generating circuit  28  and a signal receiving circuit  29 . The signal generating circuit  28  creates a stable and consistent signal at set frequencies to be placed on the telephone line  24 . The signal generating circuit  28  should be capable of supplying signals at frequencies from 1 Hz to 10 MHZ. The signal receiving circuit  29  monitors the signals on the telephone line and accurately measures the signal at the different frequency levels. The signal receiving circuit  29  should be able to read and measure signals at high frequency ranges and be able to sample and measure the line without affecting the signals on the line or the measurement of these signals. 
     FIG. 2 depicts one embodiment of the signal generating circuit of test circuit  27 . The circuit  27  includes a Digital Signal Processor (“DSP”)  30  which is connected to digital-to-analog converter (“D/A converter”)  32 . DSP  30  generates waveforms and sets the different frequency levels of the test signal. DSP  30  can generate many different signals, e.g. pulses, simulated digital signals and simultaneous sine waves, to accommodate any special requirements. D/A converter  32  takes the generated waveforms and converts the digital signal into an analog sine wave at the desired frequency. The amplifier  34 , D/A  32  and DSP  30  are all referenced to an internal circuit ground  37  which is different from the ground  22  in the telephone wire. The DSP  30 , in combination with the D/A converter  32 , is ideal for the generation of the desired waveforms because of the precision requirements of the test. Being digital, the signals generated by the DSP  30  are precise and completely controllable. In addition, the DSP&#39;s processing speed enables it to operate at very high frequencies. Such precision and speed were completely lacking in conventional analog systems. 
     The output from D/A converter  32  is connected to amplifier  34  to increase the gain of the signal. The amplifier  34  is used to ensure that the signal carries throughout the line to perform an effective testing on the lines. 
     The output from amplifier  34  is connected to impedance load  36 , which is then connected to the reference ground wire  22  in the telephone line  24 . Impedance load  36  can vary in value and is not critical to the operation of the invention. This embodiment utilizes a 1 k ohm resistance. 
     In operation, DSP  30  generates digital signals to emulate waveforms at specified frequencies. D/A converter  32  converts the signal into an analog signal which gets amplified and placed on the ground reference  22  wire. By placing the signal on the ground wire  22 , it effectively places a signal on the tip  18  and ring  20  wires of the telephone line  24  since the ground wire  22  is used as a reference point by both tip  18  and ring  20  wires. By utilizing only one signal, it also ensures that the test signal is the same for both the tip  18  and ring  20  wires. In this implementation, there is no possibility that the signal generating circuit  28  is also creating an imbalance by having slight deviations between the test signal placed on the tip and ring wires. It is the same signal for the both wires. 
     FIG. 3 depicts another embodiment of the signal generating circuit  28  of test circuit  27 . In this embodiment, the signal generator is implemented by using a numerically controlled oscillator  38  in combination with an amplifier  40  and impedance load  41 . The numerically controlled oscillator  38  can digitally generate analog sine and cosine wave forms at a programmable periodic rate. The numerically controlled oscillator  38  can also handle the high speed and precision required and the sine and cosine outputs can be adjusted over a wide range of frequencies with a high degree of resolution. The signal from the numerically controlled oscillator  38  and amplifier  40  are connected to the ground wire  22  through load resistor  41 . The tip  18  and ring  20  wires are monitored for any differences between the signal on each wire by the signal receiving circuit  29 . 
     FIG. 4 depicts one embodiment of the signal receiving circuit  29  contained within the testing circuit  27 . The receiving circuit  29  utilizes two lead wires  12 , 14  to be connected directly to the tip  18  and ring  20  wires of the telephone line  24 . These wires must be balanced themselves to prevent skewing the signal on each line and/or affecting the measurement. Both lead wires are connected to a differential amplifier  42  or high balance amplifier. The differential amplifier  42  essentially compares the two signals and outputs an amplified signal representing the difference between the signals on the tip  18  and ring  20  wires referencing the internal circuit ground  37 . The amplified signal is then input into a D/A converter  44  which is then connected to a DSP  46 . The DSP  46  used in the signal generating circuit  28  can be the same component as contained in the signal receiving circuit. 
     The operation of one embodiment of the invention can be seen by referring to the flow chart contained in FIG.  5 . First, the user must determine whether he will be using a single frequency signal or a simultaneous sine wave. Using the simultaneous sine wave allows the test to determine the balance for different frequencies with the test results are obtained much quicker, but the power requirement to generate this signal is increased. 
     For example, using a single frequency signal and increasing the frequency in gradual steps can take seconds to complete the test while a multi-tone signal or a simultaneous sine wave signal can be performed in approximately {fraction (1/100)} of the time. In contrast, the single tone signal can uses ¼ the power of the multi-tone signal. 
     If the user decides not to use a simultaneous sine wave signal, then the signal generator begins the test by creating and placing a signal on the line at a beginning frequency such as 1 kHz as seen in signal generating step  50 . The line is monitored as indicated by monitoring step  52  and the signals on both the tip  18  and ring  20  are measured and compared. The result is then recorded in recording step  54 . 
     If the user decides to use a simultaneous sine wire signal then the signal generator creates the multi-tone signal and places it on the line as demonstrated in signal generating step  51 . The signals on the lines are monitored and the level difference is measured and recorded for each frequency. The multi-tone signal does not have to encompass the whole range of desired test frequencies. 
     In either case of using a single tone or a multi-tone signal, if the last test frequency has not been used, the signal generator circuit then increases the frequency of the test signal by an incremental amount. The test can use a 3.4 kHz incremental step, which corresponds to ADSL mod points, but any incremental amount should be sufficient. 
     After the desired range of frequencies have been covered, it is possible to plot the results of the test to determine the imbalance of the telephone line  24 . FIG. 6 depicts a chart showing the results of three separate tests in accordance with the present invention. As we can see, each test starts off at frequency 10 kHz and increases in frequency by 70 kHz steps. An imbalanced measurement is taken at each frequency level. Although these three tests utilize 70 kHz increases, span a range of approximately 990 kHz and do not reach frequencies above 1 megahertz, the test can utilize any incremental amount, span a range as little as 10kHz and reach frequencies higher than 1 megahertz. 
     Previously, by testing at only 1 kHz, disturbances at different frequencies would be detected if the frequency range of the disturbance was relatively close to the 1 kHz frequency. Such disturbances, however, might only partially affect the imbalance measurement which could be interpreted as not evidencing an imbalance. By taking the imbalance measurements for each frequency tested, it becomes clear what frequencies are susceptible to being disturbed and no interpretation becomes necessary. 
     FIG. 7 depicts a graphical plot of the results from FIG.  6 . Each frequency level that the test signal was generated at constitutes a plot data point on the x axis. The y axis denotes the measurement of the balance. By plotting a graph of the test, it enables the test to have an overall picture of the balance characteristics of the telephone line and allow for the tester to determine where the telephone line is vulnerable to imbalance disturbances. For example, the line tested in Test 1 indicates that it has bad balance at the near end at the upper frequencies but has good balance at the audio band. The results from Test 2 indicate that the line is relatively evenly balanced throughout the portion of line that was tested. The plot of the third test indicates that the line has good balance at the near end and good at the audio band but has a bad balance at the far end of the line. With the results of the graphical plot, the tester does not have to rely upon an empirical standard determining the range of operating parameters. With a Wide Band Spectral Balance Analysis, the tester now can determine the areas in which a telephone line is susceptible to disturbances and at what frequencies. The slope of the line can determine if the balance is bad while the actual value or balance may be good at a particular frequency. 
     The present invention is not to be considered limited in scope by the preferred embodiments described in the specification. Additional advantages and modifications, which will readily occur to those skilled in the art from consideration of the specification and practice of the invention, are intended to be within the scope and spirit of the following claims. References to tip, ring and ground, wherein ground is an actual wire which runs with the tip and ring wires is equally applicable to a non-shielded wire which uses earth as its reference ground point.