Goto Section: 76.606 | 76.610 | Table of Contents
FCC 76.609
Revised as of October 1, 2008
Goto Year:2007 |
2009
Sec. 76.609 Measurements.
(a) Measurements made to demonstrate conformity with the performance
requirements set forth in Sec. Sec. 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 Sec. 76.605(a)(9) is met.
To demonstrate compliance with Sec. 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 Sec. 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]
Goto Section: 76.606 | 76.610
Goto Year: 2007 |
2009
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