\A^|'?^ OT Technical Memorandum 76-221 A GUIDE TO TECHNICAL STANDARDS AND MEASUREMENTS FOR CABLE TELEVISION SYaiBIVIS OT Technical Memorandum 76-221 A GUIDE TO TECHNICAL STANDARDS AND MEASUREMENTS FOR CABLE TELEVISION SYSTEMS WILLIAM C. HSIAO ^y'-'^^o. c V \ / o o U.S. DEPARTMENT OF COMMERCE ELLIOT L. RICHARDSON, Secretary BETSY ANCKER-JOHNSON. Ph.D. Assistant Secretary for Science and Technology OFFICE OF TELECOMMUNICATIONS JOHN M RICHARDSON Acting Director July 1976 UNITED STATES DEPARTMENT OF COMMERCE OFFICE OF TEL€COMMUNICATIONS STATEMENT OF MISSION The mission of the Office of Telecommunications in the Department of Commerce is to assist the Department in fostering, serving, and promoting the nation's economic development and technological advancement by improving man's comprehension of telecommuni- cation science and by assuring effective use and growth of the nation's telecommunication resources. In carrying out this mission, the Office • Conducts research needed in the evaluation and development of policy as required by the Department of Commerce • Assists other government agencies in the use of telecommuni- cations • Conducts research, engineering, and analysis in the general field of telecommunication science to meet government needs • Acquires, analyzes, synthesizes, and disseminates information for the efficient use of the nation's telecommunication re- sources. • Performs analysis, engineering, and related administrative functions responsive to the needs of the Director of the Office of Telecommunications Policy, Executive Office of the Presi- dent, in the performance of his responsibilities for the manage- ment of the radio spectrum • Conducts research needed in the evaluation and development of telecommunication policy as required by the Office of Tele- communications Policy, pursuant to Executive Order 11556 ACKNOWLEDGEMENTS The author wishes to thank the following people for their encouragement prior to and their help during the preparation of this report: Robert C. Powell of the Office of Telecom- munications, U.S. Department of Commerce, Robert S. Powers of the Federal Communications Commission, Allen Shinn of the National Science Foundation, and Delmer Ports of the National Cable Television Association. Preparation of this memorandum was supported in part by the Research Applied to National Needs program of the National Science Foundation, under grant No. SSH74-24664. This work is being published as a Technical Memorandum recognizing that the results are preliminary and for a limited audience. This work is being made available to other agencies planning to further develop standards and measurements for cable television. Ill TABLE OF CONTENTS Page ACKNOvjLEDGEMENTS iii LIST OF FIGURES vi ABSTRACT vii 1. CATV SYSTEM TECHNICAL REQUIREMENTS 1-1 1.1 Introduction 1-1 1.2 Definitions 1-1 1.3 Referenced Specifications 1-2 1.4 CATV System Design Criteria 1-3 I. Coaxial Cable 1-3 II. [lead-End Equipment 1-4 III. Trunk and Distribution Equipment. . . 1-5 IV. Passive Devices 1-7 V. General System Design 1-7 VI. Trunk System 1-8 VII. Distribution System 1-9 1.5 System Performance Guidelines 1-10 I. Head-End 1-11 II. Distribution System 1-12 1.6 System Construction Specifications 1-17 I. Construction Practices 1-17 II. Anchors and Guys 1-18 III. System Bonding and Grounding. .... 1-18 IV. Cable Installation 1-19 V. Cable Pull-Out 1-19 VI. Splices and Connectors 1-19 2. CATV SYSTEM TECHNICAL PERFORMANCE MEASUREMENTS. . 2-1 2.1 Introduction 2-1 2.1 Frequency Measurements 2-2 2.3 Visual and Aural Signal Levels 2-5 2.4 Hum Measurements 2-7 2.5 Channel Frequency Response 2-9 2.6 Car r ier-to-Noise Measurements 2-12 2.7 Co-Channel Interference Measurements. . . . 2-15 2.8 Intermodulation Measurements 2-16 2.9 Cross Modulation Measurements 2-18 2.10 Terminal Isolation Measurements 2-20 2.11 Radiation Measurements 2-23 2.12 Measurement TestSetups 2-27 iv 3. BIBLIOGRAPHY 3-1 3.1 Introduction 3-1 3.2 Head-Ends, Central Processors, and Origination Equipment 3-2 3.3 Aniplifiers and Filters 3-9 3.4 Coaxial Cables 3-14 3.5 CATV Systems 3-18 3.6 Measurements and Instrumentation 3-43 3.7 Subscriber Terminals 3-53 3.8 Interconnection of CATV Systems 3-57 3.9 Performance Standards and Specifications. . 3-50 3.10 Computers and CATV ^ 3-65 3.11 CATV System Teleservices 3-68 LIST OF FIGURES Figure £.^^ 1 Test Setup for Frequency Measurements 2-27 2 Test Setup for Frequency Measurements, Alternate Method 2-27 3 Test Setup for Signal Level Measurements 2-28 4 Test Setup for Hum Measurements 2-28 5 Test Setup .for Channel Frequency Response .... 2-28 6 Test Setup for Channel Frequency Response, Alternate Method 2-29 7 Test Setup for Measurements of Carrier to Noise, Co-Channel Interference, and Intermodulation. . . 2-29 8 Test Setup for Carrier to Woise Measurements, Alternate Method 2-29 9 Test Setup for Cross Modulation Measurements. . . 2-30 10 Test Setup for Terminal Isolation Measurements. . 2-31 11 Test Setup for Terminal Isolation Measurements, Alternate Method 2-31 12 Test SetuD for Radiation Measurements 2-31 vx A GUIDE TO TECHNICAL STANDARDS AND MEASUREMENTS FOR CABLE TELEVISION SYSTEMS William C. Hsiao* ABSTRACT The preparation of this memorandum was supported in part by Grant No. SSH74-24664 from the National Science Foundation. The National Science Foundation awarded seven grants under Phase I of the oroqram, "Design Studies for Exoerimental Application of Two-Wa/ Cable Communications to Urban Social Service Delivery and Administration." The seven grantees provided to the Foundation on January 6, 1975, detailed final proposals for the execution of aooropriate exoeriments in broadband communications. Under the NSF grant to the Office of Telecommunications, OT provided to the Foundation and the seven Phase I grantees technical advisory services, including draft versions of Sections 1 and 3 of this memorandum, to assure that the seven grantees had access to up-to-date technical information needed to adequately formulate and support their Phase II oroposals. Section 1 of the memorandum discusses CATV system technical requirements and lists referenced specifications, CATV system design criteria, system performance guidelines, and system construction specifications. Section 2 consists of ten measurement chaoters which discuss test orocedures applicable to measurement and evaluation of technical performance of CATV systems to assure comoliance with the Federal Communications Commission's Rules and Reoulations. Section 3 of the memorandum is a bibliograohy of technical literature concerned with cable television systems. The references have been organized into ten subiect areas listed in the Table of Contents and consist of 807 entries. ♦This work was done while the author was with the Office of Telecommunications, U.S. Department of Commerce, Wa«;hi nnt-nn - D.C. 7n7'^0. or Teiecommunicacions , Washington, D.C. 20230. Vli CATV SYSTEM TCCrirJICAL REQUIREMENTS 1.1 Introduction It is vital to plan, construct, test, and operate any CATV system to the highest level of technical standards permis- sible by economical constraints and achievable within the framework of current technology. To meet this objective, the following system design criteria, performance guide- lines, and construction suggestions have been developed. Deviations froin these guidelines may be reouired due to local conditions to conform to specific needs, problems, codes, etc., of its community. Tacrefore, the recommenda- tions should be considered a general guideline rather than an inflexible set of rules. 1,2 Definitions The following definitions shill apoly to terminology used in this guideline. Additional terms are defined in other portions of the guideline. • Channel — Frequency spectrum of any information carrier. • Distribution System--Any oortion of the CATV system which contains cable, oassive devices, hardware, or electronics which convey signals from the trunk caole to the subscriber droo cable. Trunk System--Any portion of the '"'">ntains cable, passive devices. CO electronics which couvtry a distribution amplifier. CATV system which -^ , hardware, or convey signals from the "head-end" to Head-End--The electronic equioment located at the start of a cable system, usually including antennas, oreampl if ier s , heterodyne processing devices, freouency converters, modulators, demodulators, aiir] other relatei equipment . 1-1 • Dictribution Amolifier — Any amplifier used in the distribution systeiH. • Trunk Amplifier — Any amplifier used in the trunk systeiTi . • Subscriber Drop — Output of subscriber tap-off device, • Subscriber Drop Cable — Cable frO'Ti subscriber drop to subscriber grounding block. • Feeder Cable or Distribution Cable--Cable used in distribution system. • Trunk Cable — Cable used in trunk system. • Active Tap — A subscriber tap-off device which has active circuitry for providing amplification of signals to the subscriber drop. • Set-top Converter — Electronic equipment used by each subscriber and placed before the television set which converts any or a block of the distributed television channels to a channel or channels on the television set . 1.3 Referenced Specifications The following applicable documents are listed for reference • Federal Communications Commission (FCC) Rules and Regulations (R&R) , Volume III, Parts 73 and 76. • American National Standards Institute (ANSI) Cl-1971, • Electronic Industry Association (EIA) R3-170. • National Cable Television Association (NCTA) Engineering Standards. • National Electric Safety Code, National Bureau of Standards Handbook No. 130. • Applicable Utility Joint Attachment Practices. 1-2 City, County, and State Codes and Ordinances. 1.4 CATV System Design Criteria (Refs. 231, 318, 402, 678, 630, 698, 707, 720) Coaxial Cable (Refs. 231, 707) A. The following coaxial cable or its equivalent shall be used in the distribution system: 1. 0.750 polyethylene foam cable with solid copper center conductor. 2. 0.500 Dolyethylene foam cable with solid copper center conductor. 3. 0.412 polyethylene foam cable with solid copper center conductor. 4. 0.750 polystyrene foam cable with copperclad aluminum center conductor. 3, These cables shall be of solid aluminum sheath for aerial plant. Underground cable installations shall be protected by a high density polyethylene jacket and a viscous flooding compound. C. Trunk and distribution coaxial cables shall have the following characteristics: 1. Characteristic impedance of 75 +2 ohms over the passband frequency range. 2. High structural return loss, nominally 26 d3 minimum in the frequency passband. 1-3 3. Maximum attenuation at 70 degrees F as follows: a. 0.412" cable attenuation at 270 MHz = 1.87 d3/100 ft. b. 0.500" cable attenuation at 270 ^MHz = 1.48 dB/100 ft. c. 0.750" cable attenuation at 270 MHz = 1.10 d3/100 ft. 4. Maximum 50 Hz AC loop resistance at 70 degrees F as follows: a. 0.412" cable — looo resistance of 2.4 oh.ns/1000 ft. b. 0.500" cable--loop resistance of 1.5 ohms/1000 ft. c. 0.750" cable — loop resistance of 0.7 ohms/1000 ft.' D. Underground Cable — All underground cable shall adhere to the above specifications. In addition, where cable is installed in buried conduit, the cable shall contain an additional moisture barrier in the form of a flooding compound interspersed between the outer polyethylene jacket and the aluminum tubing. No trunk or distribution cable shall be directly buried unless it contains a protective steel outer covering (spiral wrap or corrugated), a second polyethylene jacket orotecting the steel from corrosion, plus a moisture barrier flooding compound inside both the inner ani outer jackets. E. Subscriber Drop Cables — In the case of dual cable system, overhead drop cables should preferably be dual type to present a neat appearance. Underground installations may be separate cables. However, in either case, 100 percent shielded type cable is required. Where a dual drop is installed underground, it should either be in plastic conduit or a cable type specifically designed for direct burial for the soil conditions indigenous to the area. In any event, direct burial drop cables should DC Dreferably a dual jacket type with steel 1-4 outer wrap an of the Commission's Pules and Regulations (Pefs. 696, 697). It is not the intent of this section to outline the most elaborate techniques of measurement. The primary method, using eauipment of reasonable cost, is described for each measurement of the various parameters. Where applicable, alternate methods and eauipment are given for the measurement of several parameters. Models or manufacturers of test eauipment are not specifically given. Pertinent information in this regard can be obtained from the National Cable Television Association, Washington, D.C. In any measurement good engineering practices must be observed. In setting up test equipment all connecting cables and adaptors should be properly matched. It is desirable to use attenuator pads at connection points to minimize reflections due to mismatch. The proper impedance matching transformers or minimum loss matching pads must be used in interconnecting eauipment of different impedance levels. The insertion loss of the matching devices, the signal attenuation of connecting coaxial cables, and the gain of any preamplifier must all be taken into consideration in the measurement result. The foregoing applies to all test procedures and is not redundantly repeated for each procedure. Proper documentation of all measurements is essential. Test methods used, model and serial number of test equipment, and pertinent calibration information should be described. Sample forms for proper documentation and data recordina are given in Pef . 55] . 2-1 2.2 Freauency Measurements (Pefs. 487, 5]6, 551, 564) Prirrary Method A. Introduction The frequency of a test signal is measured in- directly by the zero beat method. A substitute signal from a signal generator is tuned until its output frequency coincides with the test signal and is displayed by a freouency counter. B. Test Equipment Peouired 1. Frequency counter. 2. PF signal generator. 3. Signal Level Meter (SLM) . 4. Variable attenuator, 75-ohm impedance, 1-dB increment . 5. Two-way hybrid splitter, two each. 6. One pair of headphones. 7. Pesistive terminator, 75 ohm. 8. (Optional) Spectrum analyzer or TV receiver. C. Test Setup Pefer to Figure 1, page 2-27. D. Test Procedure 1. Set up the eauipment as illustrated in Figure 1, page 2-27. 2. Tune SLM for a peak reading of the test signal and record level. 3. Disconnect test signal input lead to splitter No. 2, which is then terminated with the 75-ohm terminator . 2-2 4. Adjust signal generator freouency and output level so as to obtain the same reading on SLM as recorded in step D2. (Note: The signal genera- tor's full output may be required to give stable indication on some frequency counters. If so, the variable attenuator may be used to adjust the signal level fed into the SLM.) 5. Refer to step D3. Remove 75-ohm terminator. Reconnect test signal input lead to splitter No. 2, The SLM will now be receiving two signals of approximately the same frequency. 6. Adjust the signal generator's fine frequency vernier control carefully until the lowest frequency heterodyne (tone) can be heard on the headphones. (Note: When monitoring TV visual carriers, disregard the weak heterodyne, due to sidebands, appearing about 15 kHz above and below the main carrier. Use only the louder center freouency.) 7. Read and record the frequency counter indica- tion. 8. To measure TV aural carrier, the program modula- tion tends to obscure the heterodyne. Wait for a pause in the program. Then use the above procedure to obtain zero beat. 9. When measuring TV visual carrier, more precise frequency indication can be obtained by substi- tuting a TV receiver in place of the SLM and headphones combination to obtain a true "zero" beat, E. Optional Method A spectrum analyzer, if available, may be used in place of the SLM and headphones to indicate fre- quency coincidence of the test signal and the signal generator. While the spectrum analyzer is more con- venient, accuracy in the measurement depends upon the residual FM of the analyzer and how accurately the frequency coincidence is made. 2-3 II. Alternate Method z\ . Introduction The tracking generator is a soecial sicrnal source whose PF output freouency tracks (follows) some other signal beyond the tracking generator itself. In conjunction with the spectrum analyzer, the tracking generator produces a signal whose frequency orecisely tracks the soectrum analvzer tuning and can be indicated by a counter. B. Test Equioment Peauired 1. Spectrum analyzer. 2. Tracking generator. 3. Freouency counter. C. Test Setup Refer to Figure 2, oage 2-27. D. Test Procedure 1. Set up the eouioment as illustrated in Figure 2, page 2-27. 2. The spectrum analyzer /tracking qenerator system is used in the open-loop configuration. 3. The test signal is connected to the spectrum analyzer inout. 4. The tracking generator outout is connected to a freouency counter. 5. The spectrum analyzer is manually scanned to the test signal. 6. The counter displays frecruencv of the test siqnal . E. Optional Method The signal orocessor is caoable of stripping modulation and producing a direct output for a 2-4 freouency counter. When measurinq TV visual and aural carriers within its range, the signal processor can be used to receive the test signal. The processor's output is fed to a counter for readout . 2.3 Visual and Aural Signal Levels (Refs. 516, 535, 551) I. Primary Method A. Introduction Measurement of the visual and aural signal levels can be made directly from the spectrum analyzer. For greater accuracy the signal levels are measured one at a time by comparing the amplitude of each signal with the outout from a calibrated signal generator on a soectrum analyzer. The measurement can be repeated at regular intervals for a consecutive 24-hour period, if required. B. Test Equipment Required 1. Calibrated signal generator. 2. Spectrum analyzer. C. Test Setup Refer to Figure 3, page 2--28. D. Test Procedure 1. Set UP the equipment as illustrated in Figure 3, page 2-28. 2. Tune the spectrum analyzer for a maximum displayed amplitude of the test signal. 3. Center the display and use the analyzer reference level control to bring the signal level to the top graticule line of the CRT. (Note: When measuring visual signal, it is necessary to use a wide enough resolution 2-5 6. bandwidth of the analyzer to obtain sufficient spectral components. Tyoicallv, a 100 kHz bandwidth is required to read the oeak value of the carrier in terms of rms volts with the modulation on. A narrower bandwidth would show a lower than actual level.) Use the calibrated signal generator as a substitute device in olace of the test siqnal. Adjust the signal aenerator's freauency and outout level controls to duolicate the result of step D3, in order to verify the amolitude accuracy. Read the generator output level and record the result as the desired signal level. If a calibrated signal generator is not available, calibrate the spectrum analvzer using its internal calibrator. The siqnal level will then be given by the analyzer Peference Level setting. The accuracy will be a function of the analyzer's internal calibrator accuracv, the flatness of the analyzer, and the Peference Level accuracy. II. Alternate f^ethod A. Introduction A conventional signal level meter may be used for the measurement of visual and aural sionals, if a spectrum analyzer is not available. Make certain that the signal level meter is in good workinq order and has been calibrated prior to usage. B. Test Eauipment Required Siqnal level meter. C. Test Procedure 1. Connect test signal to the signal level meter. 2. Tune signal level meter for a oeak reading of the test signal. 2-6 3. Measure and record all visual and aural siqnal levels . 2.4 Hurn i^easurements (Refs. 493, 516, 551) I. Primary Method A. Introduction Hum modulation of visual carriers can show uo on the TV receiver as horizontal bars that move slowly up or down. Due to the close spacing of the modulation sidebands to the carrier, typically 60 or 120 hertz, frequency domain examination of low modulation percentage is difficult. Modulation of this type is conveniently measured in the time domain. An unmodulated carrier is tuned and detected by a spectrum analyzer used in the zero scan time domain mode. The analyzer's video output is then fed to an oscilloscope to observe and measure the ac hum. 8. Test Equipment Required 1. Soectrum analyzer 2. Osci lloscooe. 3. RF signal generator. C. Test Setup Pefer to Figure 4, page 2-28. D. Test Procedure 1. Set uo the equinment as illustrated in Figure 4, page 2-28. 2. The test signal should be unmodulated. When measuring visual carrier substitute an unmodulated carrier of the same frequency and amplitude from the signal generator. 2-7 3. Connect the analyzer's video output to the oscilloscope vertical input with a shielded lead. To minimize stray hum loops, make sure that there is no other ground on the oscillo- scope case. If the oscilloscope has a three-pin power plug, use a two-pin adapter which has no ground pin. Synchronize the oscilloscope to the "line" at a frequency of 30 or 60 hertz. 4. The analyzer is used in the zero scan time do- main mode as a filter and detector. The resolu- tion bandwidth should be set to 30 kHz. Tune the analyzer to the desired unmodulated carrier. 5. Place oscilloscope in direct-couoled mode. Adjust scope gain and centering so that, with the signal source disconnected temporarily, the trace is on the bottom line of the scope screen and, with the sianal source reconnected, the trace is in view and goes to a convenient line. Measure and record the dc voltage for later computation . 6. Switch the oscilloscope to ac coupling and center the trace vertically. Increase vertical gain of the scooe sufficiently to measure and record the peak-to-peak ac voltage for later computation. 7. Hum modulation is usually symmetrical, varving both above and below the unmodulated level. Percent modulation is given by the formula: percent modulation = 100 (E - E )/(E + E ) niax min max min or percent modulation = 100 (p-p variation)/2 (ave. level), where (p-p variation) is the ac voltage measured in step D6, where (ave. level) is the dc voltage measured in steo D5, 8. Measurement accuracy can be improved in the presence of noise by integratina the noise. This is done by shunting the vertical input of the oscilloscope with a capacitor chosen to have no effect on the amplitude of the ac comoonent. 2-8 IT. Alternate Vethod If a spectruTi analyzer is not available, a conventional signal ]evel "leter may be used for the hum measurements The use of a batterv cowered siqnal level meter is recommended to prevent any oower line "riople" from being introduced into the measurement. The test procedure is essentially the same as outlined in the primary method of 2.4 I, with the exceotion that the soectrum analvzer is reolaced by the siqna] level meter 2.5 Channel Freauency Pesponse (Pefs. 516, 551, 582) I. Primary Method A. Introduction The individual channel frequency resoonse is checked from at least 1 MHz below the visual carrier to 4 MHz above. The test is done in two parts. First, the CATV distribution system resoonse is determine'^. Then the single channel signal orocessing enuioment at the head-end is separately measured. The results of the two parts are combined to yield the overall measurement. A simultaneous sweep system is used for the test without removing TV channel from service. B. Test Equipment Required 1. Simultaneous sween transmitter. 2. Simultaneous sween receiver. 3. Marker generator. 4. Signal level meter. 5. TV receiver. 6. Camera. C. Test Setuo Refer to Fiaure 5, page 2-28. 2-9 D. Test Procedure 1. Set up the simultaneous sweep transmitter in the CATV system head-end. Usually, the sweeper can be inserted through a directional coupler ahead of the system output test point. 2. Adjust sweep output level 10 to 15 dB above the channel visual carrier level. Establish the output level in the CW mode, monitoring with signal level meter on the output test point. 3. Set up the sweeper for a 2-millisecond sweep rate and select a 5- to 20-second repetition rate. Adjust the sweep bandwidth to cover the desired frequency range, using the marker generator to define channel boundary. 4. Observe the test channel on the TV receiver to verify that interference from the simultaneous sweep system is negligible. 5. Mark trace of the reference level on the sweep receiver. Using the sweeper's built-in step attenuators, marke traces higher or lower than the reference level in desired decibel steps for further reference. 6. Bring simultaneous sweep receiver to selected test site. Connect test signal to the sweep receiver. Observe and photograph response curve. Measure channel frequency flatness using reference traces established in setp D5. 7. Return to head-end. Determine frequency response of single channel signal processing equipment. 8. Combine results of steps D6 and D7 for overall channel frequency response. II. Alternate Method A. Introduction If a simultaneous sweep system is not available, a manual point-by-point method of channel frequency response testing can be done by using a CW signal 2-10 generator at the head-end and a signal level meter at the test location. However, radio or telephone communication between the head-end and test location is required. B. Test Equipment Required 1. RF signal generator. 2. Signal level meter. C. Test Setup Refer to Figure 6, page 2-29. D. Test Procedure 1. Measure the output level of the signal processor for the channel under test at the head-end with the signal level meter. 2. Switch the signal processor to manual mode of operation. Set manual gain to give the same output level as measured in step Dl. If applicable, disable the internal substitution carrier of the signal processor. 3. Remove antenna feed for the channel under test and connect the signal generator in its place. 4. Adjust signal generator frequency and output level so that the signal processor output level is the same as measured in step Dl. 5. At the test location of the system, this signal is measured with the signal level meter. 6. The signal generator frequency is changed in desired increments, such as 0.5 MHz, to cover the required range of one MHz below the visual carrier frequency to four MHz above. For each frequency setting, make sure that signal generator output has not changed. Measure and record the signal level for each frequency. 2-11 2,6 Carr ier-to-Noise Measurements (Refs. 514, 551, 560) I. Primary Method A. Introduction The noise level in each channel is measured with a spectrum analyzer. The displayed noise level reads low due to two factors. First, the analyzer resolution bandwidth is to be normalized to the required 4 MHz, since noise power is proportional to bandwidth. The second factor is due to the log shaping and detector characteristics of the analyzer. The corrected noise level will be compared to the visual carrier level to obtain the carrier to noise ratio. B. Test Equipment Required 1. Spectrum analyzer. 2. Tunable bandpass filter, 6 MHz bandwidth. C. Test Setup Refer to Figure 7, page 2-29. D. Test Procedure 1. The test signal is connected through a tunable bandpass filter to the spectrum analyzer. 2. Tune both the filter and analyzer to the channel under test for a maximum displayed amplitude of the visual carrier. Use a 100 kHz resolution bandwidth on the analyzer, but the video filter is not used. 3. Use the reference level control of the analyzer to place this signal on the top graticule line of the CRT. 4. Tune the bandpass filter slightly to insure that the noise in the spectrum between the visual carrier and color burst is a maximum. Change the analyzer resolution bandwidth to 10 kHz. 2-12 Use sufficient video filtering to smooth out the noise display. The sweep speed of the analyzer should be slowed down to avoid "sweep rate 5. The displayed noise level should be measured directly from the analyzer screen to ascertain the number of decibels down from the top graticule line. 6. The displayed noise level is to be increased by the appropriate correction factor recommended by the analyzer manufacturer. Subtract this correction in decibels from the number of decibels obtained in step D5 to give the carrier-to-noise ratio. II. Alternate Method A. Introduction If a spectrum analyzer is not available, the conventional signal level meter, with suitable correction, can be used for the measurement of carrier-to-noise ratio^ Noise indication of the signal level meter is to be corrected upward due to normalizing of the IF bandwidth to 4 MHz. A second correction is in the opposite direction, because the peak detector commonly used by signal level meter gives higher noise reading. (Noise has a higher peak to RMS ratio than CW signals. As the detector output is reduced, its efficiency is lowered and reads closer to RMS value.) B. Test Equipment Required 1. Signal level meter (SLM) . 2. Variable attenuator, 75 ohm, range of 60 dB, in 1 dB steps. 3. Tunable bandpass filter, 6 MHz bandwidth. 4. Resistive terminator, 75 ohm. C. Test Setup Refer to Figure 8, page 2-29. 2-13 D. Test Procedure 1. Set up equipment as illustrated in Figure 8, page 2-29. 2. Switch in 60 dB of attenuation in variable attenuator . 3. Place signal level meter on its most sensitive range. 4. Tune the SLM to a peak reading at the center of visual carrier for the test channel. Adjust variable attenuator setting, SLM compensator setting, and/or SLM meter range to give a convenient reference reading, such as center scale, on the SLM. 5. At the head-end, adjust the signal processor for the test channel to manual mode of operation. Set manual controls for normal operating level. Remove antenna input lead form signal processor, and substitute a 75-ohm terminator in its place. (Disable substitute carrier generator in signal processor, if applicable.) 6. Tune the SLM carefully across the test channel for minimum noise reading. Remove attenuation from the variable attenuator until the same reference reading of step D4 is obtained. Record the amount of attenuation in decibels removed. 7. The SLM's indicated noise level is to be increased by the appropriate correction factor. (This correction factor may be determined by having the SLM calibrated on a known noise source. Otherwise, use the average correction recommended oy the SLM manufacturer.) Subtract this correction in decibels from the number of decibels obtained in step D6 for the carrier-to- noise ratio. 8. For greater noise measurement accuracy, it is desirable that all carriers be removed from the system except the pilot carriers required for automatic gain and/or slope controls. 2-14 2.7 Co-Channel Interference Measurements (Refs. 486, 516, 551) I. Primary Method A. Introduction Offset co-channel interference is measured with a calibrated spectrum analyzer of adequate selectiv- ity. The test channel signal is fed to an analyzer through a tunable bandpass filter. The filter is used to prevent the possibility of the analyzer con- tributing any distortion to the measurement. The amplitudes of the desired visual carrier and co- channel interference, if any, are displayed on the analyzer for dire.^t comparison. B. Test Equipment Required 1. Spectrum Analyzer. 2. Tunable bandpass filter, 6 MHz bandwidth. C. Test Setup Refer to Figure 7, page 2-29. D. Test Procedure 1. The test signal is connected to the spectrum analyzer through a tunable bandpass filter. 2. Tune both the filter and the analyzer to the channel under test for a maximum displayed amplitude of the visual carrier. 3. Reduce frequency scan of the analyzer to 10 kHz per division with a resolution bandwidth of 1 kHz or less. Maximum video filtering should be used so that the video information will not obscure the display. 4. Center the visual carrier display. If co- channel interference is present, it will appear as an additional carrier in a position 10 or 20 kHz either side of the visual carrier. 2-15 5. Measure and record the level of co-channel interference relative to the visual carrier. 6. For greater accuracy, set the visual carrier level at the reference level on the CRT, and read the reference level setting. Then use the reference level control to bring the interfer- ence product to the top of the CRT. Subtract these two reference level settings to get the ratio of the visual carrier signal to the co- channel interference. II. Alternate Method An approximate method may be used if a spectrum analyzer is unavailable. This method consists of visually examining the test channel (Channel A) on a TV screen for possible offset co-channel interference as indicated by "Venetian blind" effect. If such interference is observed, its level may be determined roughly by the use of a substitution oscillator. Tune the oscillator to simulate the observed co-channel beat on another TV channel free of interference (Channel B) . Display both Channels A and B simultaneously on two TV receivers. The level and frequency of the substitute oscillator signal are finely adjusted to create a similar type of interference on Channel B as that observed on Channel A. The oscillator level may then be measured by a signal level meter to give the approximate value of co-channel j.nterf erence . 2.8 Intermodulation Measurements (Refs. 493, 516, 527) I. Primary Method A. Introduction Intermodulation is defined as the generation of si- nusoidal components having frequencies equal to the sums and differences of integral multiples of the frequencies of the sinusoidal components introduced into the system. This occurs when the transfer characteristic of the system is nonlinear. Inter- modulation distortion is measured with a calibrated 2-16 spectrum analyzer of adequate selectivity. The test channel is fed to an analyzer through a tunable bandpass filter. The amplitudes of the desired visual carrier and intermodulation products are displayed on the analyzer for direct comparison. This test may be performed with modulation on in the channel under test by using maximum video filtering to eliminate the video. However, since intermodu- lation components may be present coincident with one of the discrete sidebands, it is best to turn the modulation off. B. Test Equipment Required 1. Spectrum Analyzer. 2. Tunable bandpass filter, 6 MHz bandwidth. 3. RF signal generator. C. Test Setup Refer to Figure 1, page 2-29. D. Test Procedure 1. The test signal should be unmodulated. When testing a TV channel, replace the visual carrier with an unmodulated carrier of the same frequency and amplitude from the RF signal generator at the head-end. 2. At the test location, the test signal is connected to the spectrum analyzer through a tunable bandpass filter. The filter is used to prevent the possibility of the analyzer contributing any distortion to the measurement. 3. Tune both the bandpass filter and the analyzer to the channel under test for a maximum displayed amplitude of the unmodulated carrier. 4. Set the unmodulated carrier level at the reference level on the analyzer CRT, and read the reference level setting. 5. Scan the entire channel under test carefully for discrete interference products by varying the 2-17 analyzer scan, resolution bandwidth and sweep time controls. 6. Bring the interference product to the top of the analyzer CRT with the reference level control. Read the reference level setting. 7. Subtract the reference level setting obtained in step D6 from that of step D4 to give the ratio of the intermodulation interference ratio. 8. To insure that the analyzer is not contributing distortion, change the input attenuator of the analyzer by, say, 10 dB, If all signals change by exactly 10 dB, they are real spurious interference signals and not created by the spectrum analyzer. 2.9 Cross Modulation Measurements (Refs. 493, 560, 714) I. Primary Method A. Introduction Cross modulation is the transfer or "crossing" of modulation from the interfering signal or signals to the desired signal. This occurs when the transfer characteristic of the system is nonlinear. In a CATV system, severe cross modulation results in a weak reproduction of the picture of the interfering channel superimposed on the picture being viewed. Since the receiver's horizontal scanning is synchronized with the wanted signal but usually not with the interfering one, the two horizontal frequencies usually differ slightly. Consequently, the interfering picture moves back and forth across the TV screen, producing slanting bars which give the so-called "windshield wiper" effect. The equipment required to measure cross modulation will consist of a transmitting and a receiving package. The transmitting package is a multi-carrier signal generator unit whose output frequencies correspond to the TV channel assignments of the system being tested. The carriers are 100 percent modulated 2-18 synchronously by a symmetric square wave having a frequency of 15.75 kHz. The modulation of each carrier of the multi-carrier signal generator may be individually turned on or off, and the output level of each carrier may be adjusted separately. The receiving package consists of a signal level meter (SLM) and a narrow bandwidth wave analyzer. At the test location, the SLM is tuned to a CW carrier for the channel under test, while all other channels are 100 percent modulated. The video output of the SLM is connected to the wave analyzer, which is tuned to 15.75 kHz and has been calibrated for 100 percent modulation. Read cross modulation directly on the wave analyzer. B. Test Equipment Required 1. Multicarrier signal generator unit. 2. Signal level meter (SLM). 3. Tunable bandpass filter, 6 MHz bandwidth. 4. Wave analyzer. 5. Variable attenuator, 75-ohra impedance, 1-dB increment. C. Test Setup Refer to Figure 9, page 2-30. D. Test Procedure 1. At the head-end of the CATV system replace all signals (except pilot carriers) with signals of the multi-carrier signal generator unit, whose output frequencies correspond to the frequencies of the system's visual carriers. 2. Adjust the level of each carrier to normal system operating level. 3. Turn off the modulation for the carrier of the channel under test. All other carriers are 100 percent modulated synchronously by a symmetric square wave having a frequency of 15.75 kHz. 2-19 4. At the test location, set up the equipment as illustrated in Figure 9, page 2-30. 5. Tune both the bandpass filter and the SLM for a peak reading of a modulated carrier, such as one for a channel adjacent to the channel under test. 6. Adjust the variable attenuator so that the SLM reads a signal level of +10 dBmV. 7. Connect the SLM's video output to the wave analyzer. Tune the wave analyzer for a peak reading at 15.75 kHz. Calibrate the wave analyzer for 100 percent modulation. 8. Repeat steps D5 to D7 , but tune the bandpass filter and the SLM to the unmodulated carrier of the channel under test. Read the cross modulation directly on the wave analyzer. 2.10 Terminal Isolation Measurements (Refs. 516, 535, 551) I. Primary Method A. Introduction The procedure for measuring terminal isolation involves using a leveled sweep oscillator at one subscriber terminal to sweep slowly across the frequency band of interest, and the output observed with a spectrum analyzer at an adjacent subscriber terminal. Terminal isolation is dependent, to a great degree, on the use of proper terminations at all cable outlets. B. Test Equipment Required 1. Spectrum analyzer. 2. Sweep oscillator. 2-20 C. Test Setup Refer to Figure 10, page 2-31. D. Test Procedure 1. Adjust controls of the sweep oscillator to sweep slowly across the frequency band of interest with a leveled output. 2. Measure the sweeper's output level on the spec- trum analyzer by using the analyzer's reference level control to bring the trace to the top of the CRT. Note the reference level setting. 3. Remove CATV signals from the distribution leg to be tested. Backfeed the sweep oscillator to the system from a subscriber terminal location, or a simulated one. 4. At the adjacent subscriber terminal, set the analyzer to scan the same range of frequency using a 100 kHz or greater resolution bandwidth and a rapid sweep rate. Use variable persis- tence, if available, to print out the response on the CRT. 5. Use the reference level control to bring the response trace to the top of the CRT. Read the reference level setting. Subtract this setting from the output level of the sweeper as noted in step D2 to get the terminal isolation in decibels. II. Alternate Method A. Introduction If a spectrum analyzer or sweep oscillator is not available, the terminal isolation may be measured in the following fashion. A signal from a RF signal generator is backfed into the system from one sub- scriber terminal. How much signal arriving at an adjacent subscriber terminal is measured with a signal level meter to determine the terminal isola- tion at a given frequency. The procedure is then repeated for other frequencies. 2-21 B. Test Equipment Required 1. RF signal generator. 2. Signal level meter (SLM) . 3. Variable attenuator, 75-ohm impedance, 1-dB increment. C. Test Setup Refer to Figure 11, page 2-31. D. Test Procedure 1. Remove CATV signals from the distribution leg to be tested. 2. Adjust RF signal generator controls to supply a high-level, say, +30 dBmV, signal of the desired frequency. 3. Switch in a given amount, say, 25 dB, of attenuation in variable attenuator. 4. Connect RF signal generator output through the variable attenuator to the SLM. Tune the SLM for a peak reading of the desired signal. 5. Adjust variable attenuator setting, SLM compensator setting, and/or SLM meter range to give a convenient reference reading, such as center scale, on the SLM. Record both the variable attenuator setting and the SLM reading. 6» Back-feed the signal generator output to the system from a subscriber terminal location, or a simulated one. Make sure that the generator's frequency and output level remain the same as those used in step D2. 7. At the adjacent subscriber terminal, read the signal level with the SLM through the variable attenuator. The SLM compensator setting, and/or the SLM meter range, and the variable attenuator setting remain the same as those used in step D5. 2-22 Remove attenuation from the variable attenuator until the same reference reading of step D5 is obtained on the SLM. The amount of attenuation in decibels removed gives the terminal isolation at the selected frequency. The procedure out- lined from steps Dl through D8 is repeated for other frequencies as desired. 2.11 Radiation Measurements (Refs. 526, 533, 534) I. Primary Method A, Introduction A resonant dipole antenna is used to measure an unknown field strength which can be related to the voltage measured at the end of a properly terminated transmission line, A balanced to unbalanced transi- tion, or balun, is needed to match the dipole with the unbalanced coaxial cable normally used to feed the signal to a measuring device, such as a spectrum analyzer or signal level meter, which is preceded by a broadband preamplifier to increase its sensi- tivity. The antenna length required to resonate at a given frequency (independently of any dielectric effects) depends upon the ratio of the length of the conduc- tor to its diameter. If the antenna is made of rod or tubing and is not loaded unduly near the ends by insulators, the following formula will give the required physical length of a half-wave antenna in inches: Length (inches) = (5905 x k)/f(MHz) where k is a function of the ratio of the free-space half wavelength to the conductor diameter and f is the frequency in megahertz. For all practical pur- poses, the value of k may be taken to be 0.95. Then the physical length of a resonant half wavelength antenna is given as: Length (inches) = ( 5610) /f (MHz) 2-23 when a 75-ohm, half-wave dipole antenna is exposed to an RF field, the rms voltage delivered to a 75- ohm load is: V = (The square root of 75) x 5.58 x E/f where V is the output voltage in microvolts rms, E is the field strength in microvolts per meter, and f is the signal frequency in megahertz. Conversely, if the voltage is known, the field strength is given by: E = (0.0207) (V) (f) for 75-ohm antenna. Radiation from a CATV system is likely to be both complex and different for each case. Its measure- ment will be affected by many factors, such as local standing wave conditions; ambient signals; auto ig- nition and high-level urban noises; and the presence of reflections from other wires, the ground, and nearby vehicles and buildings. It is recommended that, whenever possible, measurements of radiation be made at locations free of interference, using frequencies free of strong, off-the-air signals. If radiation is detected, probe around and find the spot where the signal is strongest to verify the measurement. B. Test Equipment Required 1. Resonant dipole antenna, 75 ohm. 2. Balanced to unbalanced balun, 75 ohm. 3. Broadband preamplifier. 4. RF signal generator. 5. Spectrum analyzer or signal level meter. C. Test Setup Refer to Figure 12, page 2-31. 2-24 D. Test Procedure 1. Adjust the physical length of the dipole antenna to be a resonant half wavelength for the fre- quency being tested in accordance with the formula discussed in the 2,11 Introduction: Length (inches) = ( 5610) /f (MHz) 2. Adjust RF signal generator controls to supply a low-level signal, say, -30 dBmV, at the test frequency to the spectrum analyzer. 3. After the analyzer has been tuned to a peak reading a- the test frequency, it is disconnected . 4. Connect the dipole antenna through the balun and the broadband preamplifier to the analyzer. 5. Keeping the antenna at the required distance from the test object, probe for presence of signal at the test frequency as monitored by the analyzer which has been pretuned in step D3. 6. If radiation is detected, maintain the specified separation while hunting for the location where the signal is strongest. 7. Record the signal level displayed by the analyzer. Make corrections due to gain of the preamplifier, loss of connecting coaxial cable, and loss of balun, if any. 8. Calculate the field strength, E in microvolts per meter, from the corrected rms voltage, V in microvolts, at the test frequency, f in megahertz, by the formula discussed in the 2.11 Introduction: E = (0.0207) X (V) X (f) for 75-ohm system. 9. Part 76, Subpart K, of the FCC Rules and Regula- tions governs the technical standards applicable to radiation from a cable television system. Section 76 .605 (a) ( 12) gives the radiation limit to be 15 microvolts per meter at a distance of 100 feet for frequencies up to and including 2-25 54 MHz, 20 microvolts per meter at a distance of 10 feet for frequencies over 54 up to and in- cluding 216 Mhz, and 15 microvolts per meter at a distance of 100 feet for frequencies over 216 MHz. 2-26 Signal Generator Test Sional 2.12 Measurement Test Setups Two-way Splitter #1 o Varialjle Attenuator Frequency Counter Signal Lever Meter Two-way Splitter i2 Figure 1. Test Setup for Freauency Measurements Test ^ Spectrum Analyzer Tracking Generator Ik Freauency Counter Signal Figure 2, Test Setup for Frequency Measurements, Alternate Method 2-27 Test Signal Spectrum Analyzer Precision Amplitude Signal Generator Figure 3. Test Setup for Signal Level ?*'easurements Test Signal Spectrum Analyzer Oscilloscone Figure 4. Test Setup for Hum r!easurements Simultaneous Sv;eep Transmitter i Marker Generator System or Equipment Under Test ■♦ Simultaneous Receiver T^iaure 5. Test Setup for Channel Frequency Response 2-28 signal Generator Systera or Eauipnent Under Test Is Signal I.evnr Meter w r Figure 6. Test Setup for Channel Frequency Response, Alternate Method Test Signal Tunable Bandpass Filter Spectrum Analyzer Figure 7. Test Setup for r'.easurenents of Carrier to Noise, Co-Channel Interference, and Internodulation Test Signal Tunable Bandpass Filter Variable Attenuator Signal Level Meter Figure 8. Test Setup for Carrier to TToise ^^easurenents , Alternate T'letiiod 2-29 u 0) N >^ (0 frt c S: < 4>. iH fO M ^) C Q) Q) & > -U ■M •H ^ o QJ (L -P 1^ .H (0 X! 3 c fd c •H CU •H M 4J +J n3 4J (t? > <; fH p ^ k w m w nH (0 M M X! a i tr c W W D 0) v^ 4 k •H ^ QJ •H )-l ^1 M (t3 U 4J 1 rH (0 •H ft3 M -U C munications technology for planned development of Connecticut, Connecticut Research Commission, Hartford, Connecticut. 786. Ledbetter, T. (1971), CATV and the cities (problems and promises), 20th Annual NCTA Convention, Official Transcript. 787. Macy, J. (1971), Community uses of public television. City, 5, pp. 23-25. 788. Mason, W. and S. Polk (1972), Revolutionizing home communications, the MITRE Corporation, M72-33. 789. McCormick, E. (1972), Cable television: a community information system at Jonathan, 21st Annual NCTA Convention, Official Transcript, Technical Volum.e. 790. McManamon, P. (1975), Technical implications of a teleconference service, IEEE Transactions on Communi- cations, Special Issue on Interactive Broadband Cable Systems, January. 3-70 791. Hetcalf, R. (1971), CATV and the cities (problems and promises), 20th Annual NCTA Convention, Official Transcript . 792. Moeller, J. (1971), CATV ancillary services, 20th Annual NCTA Convention, Official Transcript. 793. rlational Academy of Enqineerinq (1969), Educational technology in higher education: the promises and limitations of ITV and CAI , Commission on Education, September . 794. National Academy of Engineering (1969), Telecommuni- cations for enhanced metropolitan function and form. Committee on Telecommunications, Washington, D.C. 795. Pearson, H. (1974), Public access — community response, IEEE Intercon Technical Papers, IEEE Inter- national Convention and Exposition, March. 796. Raynor, H. Jr. (1969), Charleston's computerized traffic control system. Traffic Engineering and Control, May. 797. Hockoff, H. (1975), An overview of some technological/health care system implications of seven exploratory broadband communication experiments in health services delivery, IEEE Transactions on Communications, Special Issue on Interactive Broadband Cable Systems, January. 79fa. Roth, S. and R. Noyer (1970) , Automatic vehicle monitoring and control in an urban environment, the American Society of Mechanical Engineers, New York, N.Y., 7 0-TRAN-4 0. 799. Schlafly, H. (1971), A cable caster discusses what services can be obtained from different two-way systems. Electronics, 44 (20). 800. Stetten, K. (1971), Interactive television software for cable television applications, the MITRE Corporation, MTP-3 54. aoi. stetten, K. (1971), The technology of small local facilities for instructional use, MITRE Report MTP-347, January . 3-71 802. Stetten, K. (1972) , A study of the technical and economic considerations attendant on the home delivery of instruction and other socially-related services via interactive Cable TV, MITRE Report M72-200, December. 803. Tate, C. (ed.) (1971), Cable television in the cities: community control, public access, and minority ownership, Washington, D.C., the Urban Institute. 804. TV Communications (1972), Sterling Manhattan: serving the multitude. Vol. 9, January. 805. Ulicki, E. (1973), Security surveillance for offices, institutions, hotels, and apartments using existing cabling, IEEE Electronic Security Systems Seminar, pp. 20-27. 805. Vicom Manufacturing Company (1971), Interaction television, services to subscribers, Ann Arbor, Michigan, March. 807. Wallerstein, E., C. Marshall, and R. Alexander (1973), Pediatrics and cable television, 22nd Annual NCTA Convention, Official Transcript, Technical Volume. 3-72 FORM OT-29 (3-731 U.S. DEPARTMENT OF COMMERCE Office of telecommunications BIBLIOGRAPHIC DATA SHEET I. PUBLICATION OR REPORT NO. 2. Cov't Accession No. 3. Recipient's Accession No 4. TITLE AND SUBTITLE A GUIDE TO TECHNICAL STANDARDS AND MEASUREMEOTS FOR CABLE TELEVISION SYSTEMS 5. Publication Date 6, Performtng Organization C,ode 7. AUTHOR(S) William C. Hsiao 9. Pro|ect/Task/Work Unit No. 8. PERFORMING ORGANIZATION NAME AND ADDRESS Telecommunications Analysis Division Office of Teleconnnunications U. S. Department of Commerce Washington, D.C. 20230 10. Contract /Grant No. NSF Grant No. SSH74-24664 (in part) 11. Sponsoring Organization Name and Address 12, Type of Report and Period Covered 13. 14. SUPPLEMENTARY NOTES 15. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography of literature survey, mention it here.) The preparation of this report was supported in part by Grant No. SSH74-24664 from the National Science Foundation. The National Science Foundation awarded seven grants under Phase I of the program, "Design Studies for Experimental Appli cation of Two-Way Cable Communications to Urban Social Service Delivery and Ad- ministration." The seven grantees provided to the Foundation on January 6, 1975, detailed final proposals for the execution of appropriate experiments in broad- band communications. Under the NSF grant to the Office of Telecommunications, OT provided to the Foundation and the seven Phase I grantees technical advisory services, including draft versions of Sections 1 and 3 of this report, to assure that the seven grantees had access to up-to-date technical information needed to adequately formulate and support their Phase II proposals. Section 1 of the report discusses CATV system technical requirements and lists referenced specifications, CATV system design criteria, system performance guide- lines, and system construction specifications. Section 2 consists of ten measurement chapters which discuss test procedures applicable to measurement and evaluation of technical performance of CATV systems to assure compliance with the Federal Communications Commission's Rules and Regulations. Section 3 of the report is a bibliography of technical literature concerned with cable television systems. The references have been organized into ten subject areas listed in the Table of Contents and consist of 807 entries. 16. KEY WORDS (alphabetical order, separated by semicolons) Bibliography; Cable television; Design criteria; FCC; Performance guidelines; Specifications; Technical requirements 17. AVAILABILITY STATEMENT n UNLIMITED. n FOR OFFICIAL DISTRIBUTION. 18. Stt ur 1 ly I lass (This report ) Nonclassified 19. Security Class (This pcifii- ) 20. Numhcr ot p.iRc 131 21. P 3-73 I'SCOMM-OC i9716-P73 •fr US ammmm pwwting ottki: m^ 210-801/J42