Apparatus and method for measuring loop insertion loss single-endedly

1. A system for determining insertion loss of a telephone line under test (LUT) comprising:

low frequency test hardware comprising:

means for electrically stimulating the LUT at a first plurality of frequencies;

means for determining for each frequency of the first plurality of frequencies an input impedance Z 2tr of the LUT at said frequency in response to the electrical stimulation at said frequency;

means for determining values for at least two of Rs, Cs, Rp and Cp from Z 2tr at each frequency of the first plurality of frequencies, wherein Rs and Cs are the corresponding series RC equivalent components of Z 2tr and Rp and Cp are corresponding parallel RC equivalent components of Z 2tr ; and

means for determining a first value insertion loss of the LUT as a function of a value of one of Rs, Cs, Rp and Cp determined at one frequency of the first plurality of frequencies and a value of another one of Rs, Cs, Rp and Cp at another frequency of the first plurality of frequencies;

high frequency test hardware comprising:

means for electrically stimulating the LUT at a second plurality of frequencies;

means for determining for each frequency of the second plurality of frequencies an input impedance Zin of the LUT at said frequency in response to the electrical stimulation at said frequency and a length (d) of the LUT as a function of Zin at said frequency;

means for determining for each frequency of a subset of the second plurality of frequencies a running standard deviation of the length d of the LUT, wherein the running standard deviation for each frequency is determined as a function of the lengths d determined at and below said frequency;

means for determining which pair of adjacent frequencies of the subset of the second plurality of frequencies where the largest difference between running standard deviations occurs;

means for determining a mean length (dm) of the LUT as a function of the lengths d of the LUT determined for each frequency at and below one of said pair of adjacent frequencies;

means for determining a gauge of the LUT as a function of the running standard deviation of the one of said pair of adjacent frequencies; and

means for determining a second value insertion loss of the LUT as a function of the gauge and the mean length dm; and

means for comparing the values of the first and second insertion losses to an expected insertion loss value for the LUT and for designating one of said first, second and expected insertion loss values as the actual insertion loss value for the LUT.

2. The system of claim 1 , wherein:

the first plurality of frequencies includes frequencies between 100 Hz and 7 kHz inclusive; and

the second plurality of frequencies includes frequencies between 1000 kHz and 120 kHz inclusive.

3. The system of claim 1 , wherein:

adjacent pairs of frequencies of the first plurality of frequencies are about 100 Hz apart; and

adjacent pairs of frequencies of the second plurality of frequencies are about 610.4 Hz apart.

4. The system of claim 1 , wherein the means for determining the input impedance Z 2tr of the LUT at each frequency of the first plurality of frequencies includes means for canceling out the effect of a test path disposed between the low frequency test hardware and the LUT on said determination at each frequency.

5. The system of claim 4 , wherein the means for canceling out the effect of the test path:

determines open circuit, short circuit and resistive termination responses of the test path to electrical stimulus at each frequency of the first plurality of frequencies;

determines at least one compensation constant for each frequency of the first plurality of frequencies; and

mathematically combines the at least one compensation constant for each frequency of the first plurality of frequencies with a corresponding value of Z 2tr measured at said frequency to obtain the value of Z 2tr at said frequency that is utilized to determine the values for at least two of Rs, Cs, Rp and Cp at said frequency.

6. The system of claim 5 , wherein:

the open circuit termination is a resistor having a value of greater than 10 Meg ohms;

the short circuit termination is a resistor having a value of approximately 3 ohms; and

the resistive termination is a resistor having a value of approximately 900 ohms.

7. The system of claim 1 , wherein the means for determining the input impedance Zin of the LUT at each frequency of the second plurality of frequencies includes means for canceling out the effect of a test path disposed between the high frequency test hardware and the LUT on said determination at each frequency.

8. The system of claim 7 , wherein the means for canceling out the effect of the test path:

determines open circuit, short circuit and resistive termination responses of the test path to electrical stimulus at each frequency of the second plurality of frequencies;

determines at least one compensation constant for each frequency of the second plurality of frequencies; and

mathematically combines the at least one compensation constant for each frequency of the second plurality of frequencies with a corresponding value of Zin measured at said frequency to obtain the value of Zin at said frequency that is utilized to determine the length d of the LUT at said frequency.

9. The system of claim 8 , wherein:

the open circuit termination is a resistor having a value of greater than 10 Meg ohms;

the short circuit termination is a resistor having a value of approximately 3 ohms; and

the resistive termination is a resistor having a value of approximately 160 ohms.

10. A method of determining insertion loss of a telephone line under test (LUT) comprising:

(a) electrically stimulating the LUT at a first plurality of frequencies;

(b) determining for each frequency of the first plurality of frequencies an input impedance Z 2tr of the LUT at said frequency in response to the electrical stimulation at said frequency;

(c) determining values for at least two of Rs, Cs, Rp and Cp from Z 2tr at each frequency of the first plurality of frequencies, wherein Rs and Cs are the corresponding series RC equivalent components of Z 2tr and Rp and Cp are corresponding parallel RC equivalent components of Z 2tr ;

(d) determining a first value insertion loss of the LUT as a function of a value of one of Rs, Cs, Rp and Cp determined at one frequency of the first plurality of frequencies and a value of another one of Rs, Cs, Rp and Cp at another frequency of the first plurality of frequencies;

(e) electrically stimulating the LUT at a second plurality of frequencies;

(f) determining for each frequency of the second plurality of frequencies an input impedance Zin of the LUT at said frequency in response to the electrical stimulation at said frequency and a length (d) of the LUT as a function of Zin at said frequency;

(g) determining for each frequency of a subset of the second plurality of frequencies a running standard deviation of the length d of the LUT, wherein the running standard deviation for each frequency is determined as a function of the lengths d determined at and below said frequency;

(h) determining which pair of adjacent frequencies of the subset of the second plurality of frequencies where the largest difference between running standard deviations occurs;

(i) determining a mean length (dm) of the LUT as a function of the lengths d of the LUT determined for each frequency at and below one of said pair of adjacent frequencies;

(j) determining a gauge of the LUT as a function of the running standard deviation of the one of said pair of adjacent frequencies;

(k) determining a second value insertion loss of the LUT as a function of the gauge and the mean length dm; and

(l) comparing the values of the first and second insertion losses to an expected insertion loss value for the LUT and for designating one of said first, second and expected insertion loss values as the actual insertion loss value for the LUT.

11. The method of claim 10 , wherein the step of determining the input impedance Z 2tr of the LUT at each frequency of the first plurality of frequencies includes canceling out the effect of a test path disposed between the low frequency test hardware and the LUT on said determination at each frequency.

12. The method of claim 11 , wherein the step of canceling out the effect of the test path includes:

determining open circuit, short circuit and resistive termination responses of the test path to electrical stimulus at each frequency of the first plurality of frequencies;

determining at least one compensation constant for each frequency of the first plurality of frequencies; and

mathematically combining the at least one compensation constant for each frequency of the first plurality of frequencies with a corresponding value of Z 2tr measured at said frequency to obtain the value of Z 2tr at said frequency that is utilized to determine the values for at least two of Rs, Cs, Rp and Cp at said frequency.

13. The method of claim 10 , wherein the step of determining the input impedance Zin of the LUT at each frequency of the second plurality of frequencies includes canceling out the effect of a test path disposed between the high frequency test hardware and the LUT on said determination at each frequency.

14. The method of claim 13 , wherein the step of canceling out the effect of the test path includes:

determining open circuit, short circuit and resistive termination responses of the test path to electrical stimulus at each frequency of the second plurality of frequencies;

determining at least one compensation constant for each frequency of the second plurality of frequencies; and

mathematically combining the at least one compensation constant for each frequency of the second plurality of frequencies with a corresponding value of Zin measured at said frequency to obtain the value of Zin at said frequency that is utilized to determine the length d of the LUT at said frequency.