§  76.609   Measurements.

   (a) Measurements made to demonstrate conformity with the performance
   requirements set forth in § §  76.601 and 76.605 shall be made under
   conditions which reflect system performance during normal operations,
   including the effect of any microwave relay operated in the Cable
   Television Relay (CARS) Service intervening between pickup antenna and
   the cable distribution network. Amplifiers shall be operated at normal
   gains, either by the insertion of appropriate signals or by manual
   adjustment. Special signals inserted in a cable television channel for
   measurement purposes should be operated at levels approximating those
   used for normal operation. Pilot tones, auxiliary or substitute
   signals, and nontelevision signals normally carried on the cable
   television system should be operated at normal levels to the extent
   possible. Some exemplary, but not mandatory, measurement procedures are
   set forth in this section.

   (b) When it may be necessary to remove the television signal normally
   carried on a cable television channel in order to facilitate a
   performance measurement, it will be permissible to disconnect the
   antenna which serves the channel under measurement and to substitute
   therefor a matching resistance termination. Other antennas and inputs
   should remain connected and normal signal levels should be maintained
   on other channels.

   (c) As may be necessary to ensure satisfactory service to a subscriber,
   the Commission may require additional tests to demonstrate system
   performance or may specify the use of different test procedures.

   (d) The frequency response of a cable television channel may be
   determined by one of the following methods, as appropriate:

   (1) By using a swept frequency or a manually variable signal generator
   at the sending end and a calibrated attenuator and frequency-selective
   voltmeter at the subscriber terminal; or

   (2) By using either a multiburst generator or vertical interval test
   signals and either a modulator or processor at the sending end, and by
   using either a demodulator and either an oscilloscope display or a
   waveform monitor display at the subscriber terminal.

   (e) System noise may be measured using a frequency-selective voltmeter
   (field strength meter) which has been suitably calibrated to indicate
   rms noise or average power level and which has a known bandwidth. With
   the system operating at normal level and with a properly matched
   resistive termination substituted for the antenna, noise power
   indications at the subscriber terminal are taken in successive
   increments of frequency equal to the bandwidth of the
   frequency-selective voltmeter, summing the power indications to obtain
   the total noise power present over a 4 MHz band centered within the
   cable television channel. If it is established that the noise level is
   constant within this bandwidth, a single measurement may be taken which
   is corrected by an appropriate factor representing the ratio of 4 MHz
   to the noise bandwidth of the frequency-selective voltmeter. If an
   amplifier is inserted between the frequency-selective voltmeter and the
   subscriber terminal in order to facilitate this measurement, it should
   have a bandwidth of at least 4 MHz and appropriate corrections must be
   made to account for its gain and noise figure. Alternatively,
   measurements made in accordance with the NCTA Recommended Practices for
   Measurements on Cable Television Systems, 2nd edition, November 1989,
   on noise measurement may be employed.

   (f) The amplitude of discrete frequency interfering signals within a
   cable television channel may be determined with either a spectrum
   analyzer or with a frequency-selective voltmeter (field strength
   meter), which instruments have been calibrated for adequate accuracy.
   If calibration accuracy is in doubt, measurements may be referenced to
   a calibrated signal generator, or a calibrated variable attenuator,
   substituted at the point of measurement. If an amplifier is used
   between the subscriber terminal and the measuring instrument,
   appropriate corrections must be made to account for its gain.

   (g) The terminal isolation between any two terminals in the cable
   television system may be measured by applying a signal of known
   amplitude to one terminal and measuring the amplitude of that signal at
   the other terminal. The frequency of the signal should be close to the
   midfrequency of the channel being tested. Measurements of terminal
   isolation are not required when either:

   (1) The manufacturer's specifications for subscriber tap isolation
   based on a representative sample of no less than 500 subscribers taps
   or

   (2) Laboratory tests performed by or for the operator of a cable
   television system on a representative sample of no less than 50
   subscriber taps, indicates that the terminal isolation standard of
   §  76.605(a)(9) is met.

   To demonstrate compliance with §  76.605(a)(9), the operator of a cable
   television system shall attach either such manufacturer's
   specifications or laboratory measurements as an exhibit to each
   proof-of-performance record.

   (h) Measurements to determine the field strength of the signal leakage
   emanated by the cable television system shall be made in accordance
   with standard engineering procedures. Measurements made on frequencies
   above 25 MHz shall include the following:

   (1) A field strength meter of adequate accuracy using a horizontal
   dipole antenna shall be employed.

   (2) Field strength shall be expressed in terms of the rms value of
   synchronizing peak for each cable television channel for which signal
   leakage can be measured.

   (3) The resonant half wave dipole antenna shall be placed 3 meters from
   and positioned directly below the system components and at 3 meters
   above ground. Where such placement results in a separation of less than
   3 meters between the center of the dipole antenna and the system
   components, or less than 3 meters between the dipole and ground level,
   the dipole shall be repositioned to provide a separation of 3 meters
   from the system components at a height of 3 meters or more above
   ground.

   (4) The horizontal dipole antenna shall be rotated about a vertical
   axis and the maximum meter reading shall be used.

   (5) Measurements shall be made where other conductors are 3 or more
   meters (10 or more feet) away from the measuring antenna.

   (i) For systems using cable traps and filters to control the delivery
   of specific channels to the subscriber terminal, measurements made to
   determine compliance with §  76.605(a) (5) and (6) may be performed at
   the location immediately prior to the trap or filter for the specific
   channel. The effects of these traps or filters, as certified by the
   system engineer or the equipment manufacturer, must be attached to each
   proof-of-performance record.

   (j) Measurements made to determine the differential gain, differential
   phase and the chrominance-luminance delay inequality (chroma delay)
   shall be made in accordance with the NCTA Recommended Practices for
   Measurements on Cable Television Systems, 2nd edition, November 1989,
   on these parameters.

   [ 37 FR 3278 , Feb. 12, 1972, as amended at  37 FR 13867 , July 14, 1972;
    41 FR 10067 , Mar. 9, 1976;  42 FR 21782 , Apr. 29, 1977;  49 FR 45441 ,
   Nov. 16, 1984;  57 FR 11004 , Apr. 1, 1992;  57 FR 61011 , Dec. 23, 1992;
    58 FR 44952 , Aug. 25, 1993]

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