In-service cable television measurements

Claim 1

An apparatus of the type for performing measurements in the frequency domain including means for displaying a frequency spectrum and means for tuning to a desired frequency within the frequency spectrum, the apparatus comprising: means for generating for the desired frequency a final intermediate frequency signal from an input radio frequency composite television signal having a channel carrier frequency; means for detecting from the final intermediate frequency signal a composite video signal; means for generating from the composite video signal a trigger signal for triggering the displaying means during an unmodulated portion of the composite video signal; means for sampling the composite video signal when the desired frequency is offset from the channel carrier frequency to obtain an average of the amplitude of the composite video signal between sync pulses during the unmodulation portion; and means for computing from a peak amplitude of the sync pulses, determined when the desired frequency is the channel carrier frequency, and the average of a point midway between two sync pulses within the unmodulated portion a carrier-to-noise ratio for the carrier frequency.

Claim 2

An apparatus of the type for performing measurements in the frequency domain including means for displaying a frequency spectrum and means for tuning to a desired frequency within the frequency spectrum, the apparatus comprising: means for generating for the desired frequency a final intermediate frequency signal from an input radio frequency composite television signal having a channel carrier frequency; means for detecting from the final intermediate frequency signal a composite video signal; means for generating from the composite video signal a trigger signal for triggering the displaying means during an unmodulated portion of the composite video signal; means for sampling the composite video signal when the desired frequency is offset from the channel carrier frequency to obtain an average of the amplitude of the composite video signal between sync pulses during the unmodulation portion; and means for computing from a peak amplitude of the sync pulses, determined when the desired frequency is the channel carrier frequency, and the average of a point midway between two sync pulses within the unmodulated portion a carrier-to-noise ratio for the carrier frequency.

Claim 5

A method of measuring carrier to noise ratio of a composite radio frequency television signal using a frequency domain instrument comprising the steps of: tuning the frequency domain instrument to a specific channel carrier frequency from among a plurality of channel carrier frequencies contained within the composite radio frequency television signal; measuring with the frequency domain instrument the specific channel carrier frequency and a peak amplitude of the sync pulses for a composite video signal from the specific channel carrier frequency; offsetting the frequency domain instrument from the specific channel carrier frequency; sampling the composite video signal during the unmodulated portion to obtain an average of the amplitude between sync pulses; and computing the carrier-to-noise ratio for the channel carrier frequency as a function of the peak amplitude of the sync pulses and of the average for a sample point midway between two sync pulses.

Claim 6

A method of measuring carrier to noise ratio of a composite radio frequency television signal using a frequency domain instrument comprising the steps of: tuning the frequency domain instrument to a specific channel carrier frequency from among a plurality of channel carrier frequencies contained within the composite radio frequency television signal; measuring with the frequency domain instrument the specific channel carrier frequency and a peak amplitude of the sync pulses for a composite video signal from the specific channel carrier frequency; offsetting the frequency domain instrument from the specific channel carrier frequency; sampling the composite video signal during the unmodulated portion to obtain an average of the amplitude between sync pulses; and computing the carrier-to-noise ratio for the channel carrier frequency as a function of the peak amplitude of the sync pulses and of the average for a sample point midway between two sync pulses.

Claim 7

A method of measuring a composite triple beat ratio for a cable television system of the type having a headend unit and a distribution system comprising the steps of: measuring a peak amplitude of sync tips for a selected channel on the distribution system using a frequency domain instrument ; offsetting at the headend unit the carrier frequency of the selected channel by a predetermined amount during specified lines of the composite video signal of the selected channel that have no modulation; sampling the selected channel during the specified lines to obtain an average of the amplitude of the composite video signal; measuring the amplitude of the average for a sample point at the end of the specified lines; computing the composite triple beat ratio as a function of the peak amplitude of the sync tips and of the average of the sample point.

Claim 8

A method of measuring a composite triple beat ratio for a cable television system of the type having a headend unit and a distribution system comprising the steps of: measuring a peak amplitude of sync tips for a selected channel on the distribution system using a frequency domain instrument ; offsetting at the headend unit the carrier frequency of the selected channel by a predetermined amount during specified lines of the composite video signal of the selected channel that have no modulation; sampling the selected channel during the specified lines to obtain an average of the amplitude of the composite video signal; measuring the amplitude of the average for a sample point at the end of the specified lines; computing the composite triple beat ratio as a function of the peak amplitude of the sync tips and of the average of the sample point.

Claim 13

An apparatus for performing measurements on a cable television system of the type having a headend for generating a radio frequency composite television signal having a plurality of channels, each channel having a unique carrier frequency, and having a distribution system for carrying the radio frequency composite television signal to a receiver, the apparatus comprising: a headend unit coupled between a television signal source and a combiner in the headend for offsetting upon command the carrier frequency of a selected one of the channels a predetermined amount during specified television lines during an unmodulated portion of the selected channel; and a frequency domain instrument coupled to the distribution system for measuring the carrier frequency of the selected channel, for determining a peak sync tip amplitude for the selected channel when tuned to the carrier frequency, for determining at a frequency of the frequency domain instrument offset from the carrier frequency a noise amplitude between two sync tips within an unmodulated portion of the selected channel, for determining a triple beat amplitude at the end of the specified television lines when the headend unit is commanded to offset the carrier frequency of the selected channel a small amount, and for calculating from the peak sync tip amplitude, the noise amplitude and the triple beat amplitude a carrier-to-noise ratio and a triple beat ratio for the cable television system.

Claim 14

An apparatus for performing measurements on a cable television system of the type having a headend for generating a radio frequency composite television signal having a plurality of channels, each channel having a unique carrier frequency, and having a distribution system for carrying the radio frequency composite television signal to a receiver, the apparatus comprising: a headend unit coupled between a television signal source and a combiner in the headend for offsetting upon command the carrier frequency of a selected one of the channels a predetermined amount during specified television lines during an unmodulated portion of the selected channel; and a frequency domain instrument coupled to the distribution system for measuring the carrier frequency of the selected channel, for determining a peak sync tip amplitude for the selected channel when tuned to the carrier frequency, for determining at a frequency of the frequency domain instrument offset from the carrier frequency a noise amplitude between two sync tips within an unmodulated portion of the selected channel, for determining a triple beat amplitude at the end of the specified television lines when the headend unit is commanded to offset the carrier frequency of the selected channel a small amount, and for calculating from the peak sync tip amplitude, the noise amplitude and the triple beat amplitude a carrier-to-noise ratio and a triple beat ratio for the cable television system.