Goto Section: 76.607 | 76.610 | Table of Contents
Revised as of September 1, 2021
Goto Year:2020 |
§ 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
(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
(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
(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
(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]
Goto Section: 76.607 | 76.610
Goto Year: 2020 |
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