Technique for estimation of a subscriber line insertion loss
View Patent ↗A method and apparatus for pre-qualifying lines with respect to estimating the insertion loss of the line is presented. End-to-end insertion loss at high frequencies is estimated from measurements made at low frequencies through the voice switch at the central office of a telephone company. An AC voltage waveform is applied to the telephone line being tested. Real and imaginary components of the resultant waveform are measured. These measurements are captured and used to estimate the insertion loss of the telephone line at frequencies in the range of 40 kHz to 300 kHz.
1. A computer program product for a test unit, the computer program product comprising a computer usable medium having computer readable code thereon, including program code comprising:
instructions and data for causing a processor to perform at least one of interconnecting two wires of a phone line to each other, measuring a capacitance between said phone line and ground, applying an AC voltage between said phone line and ground, measuring a resulting voltage between said phone line and ground, measuring a current of said telephone line, and estimating an insertion loss of said phone line.
2. The computer program product of claim 1 wherein said instructions and data include commands for measuring a capacitance between the phone line and ground at a frequency of less than approximately 1 kHz.
3. The computer program product of claim 1 wherein said instructions and data include commands for applying an AC voltage having a frequency between approximately 2 kHz and approximately 6 kHz.
4. The computer program product of claim 1 wherein said instructions and data include commands for applying an AC having a frequency of less than approximately 5 kHz.
5. The computer program product of claim 1 wherein said instructions and data include commands for estimating an insertion loss of a telephone line between approximately 40 kHz and approximately 300 kHz.
6. The computer program product of claim 1 wherein said instructions and data include commands for estimating an insertion loss of a telephone line at approximately 100 kHz.
7. The computer program product of claim 1 wherein said instructions and data include commands for estimating an insertion loss of a telephone line according to the formula:
5000
(
Z
2
+
[
1
/
ω
C
]
2
)
dB
wherein Z is equal to said voltage divided by said current, C is equal to said capacitance and ω is a 2π times a driving frequency.