CEA-544-C-2010 Low Frequency Immunity of Tuners in a Cable System《电缆系统中调谐器的低频抗扰性》.pdf

1、 CEA Standard Low Frequency Immunity of Tuners in a Cable System CEA-544-C R-2014 September 2014 NOTICE Consumer Electronics Association (CEA) Standards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers a

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7、ohibits unauthorized reproduction of this document by any means. Organizations may obtain permission to reproduce a limited number of copies by entering into a license agreement. Requests to reproduce text, data, charts, figures or other material should be made to CEA. (Formulated under the cognizan

8、ce of the CEA R4 Video Systems Committee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2014 Technology & Standards Department www.CE.org All rights reserved CEA-544-C R-2014 i FOREWORD This standard was developed under the auspices of the Consumer Electronics Association (CEA) R4 Video Systems Com

9、mittee. Signals on cable systems below channel 2 may cause interference on broadcast receivers, especially on the low VHF channels. The return data channel signals for television cable and internet services using cable connection in the range of 5 to 42 MHz are generated by return devices such as in

10、-home internet modems, set top boxes and two-way cable ready television receivers, any of which may be in close proximity to television receivers tuned to low VHF channels. CEA-544-C references the levels to which the tuner should be immune in the 5 54 MHz range, and it describes a test method to de

11、termine the tuners immunity at those levels. CEA-544-C supersedes CEA-544-B. CEA-544-C R-2014 ii This page intentionally left blank. CEA-544-C R-2014 iii CONTENTS 1 Scope. 1 2 References 1 2.1 Regulatory References. 1 2.1.1 Regulatory Reference List . 1 2.1.2 Regulatory Reference Acquisition 1 3 Req

12、uirements . 1 4 Measurement Procedure for Immunity of TV Tuners to Harmonically Generated Interference 1 4.1 Objective 1 4.2 Measurement of Interference Immunity . 1 4.3 Procedure 2 4.3.1 Equipment List 2 4.3.2 Equipment Diagram 2 4.4 Measurement Procedure 2 4.5 Setup of Spectrum Analyzer 4 4.6 Repe

13、at at Other Operating Conditions . 4 Tables Table 1 Example of Typical Spectrum Analyzer Control Settings . 4 Figures Figure 1 Measurement Equipment Diagram . 2 CEA-544-C R-2014 iv This page intentionally left blank. CEA-544-C R-2014 1 Low Frequency Immunity of Tuners in a Cable System 1 Scope CEA-5

14、44-C defines the measurement procedures for the low frequency (5-54 MHz) immunity of tuners in a cable system, based on requirements in FCC regulations that define the assumed levels of the desired signal, low frequency interference and the required receiver immunity. These procedures define the spe

15、cific tests needed to determine compliance with the requirements. 2 References The following regulatory references contain provisions that, through reference in this text, constitute normative provisions of this standard. 2.1 Regulatory References 2.1.1 Regulatory Reference List FCC Regulations, 47

16、C.F.R. 76.605, Multichannel Video and Cable Television Service, Technical Standards FCC Regulations, 47 C.F.R. 15.123(c)(1), Labeling of Digital Cable Ready Products FCC Regulations, 47 C.F.R. 15.38, Incorporations by Reference 2.1.2 Regulatory Reference Acquisition FCC Regulations: FCC Regulations,

17、 http:/www.access.gpo.gov/nara/cfr/cfr-table-search.html 3 Requirements A television receiver or video cassette recorder (VCR) in the play-thru mode (i.e., output to the TV receiver on Ch 3/4) tuned to any channel, shall have an interference output at least 53 dB below the desired signal at the IF o

18、utput of the tuner within the 6 MHz IF bandwidth, which is typically 41 MHz to 47 MHz, when measured according to the procedure in CEA-544-B with signal levels as follows: a) Interfering carrier: 7 dBm (42 dBmV) 5 MHz 30 MHz 25 dBm (24 dBmV) 30 MHz 41 MHz 49 dBm (0 dBmV) 41 MHz 48 MHz 59 dBm (-10 dB

19、mV) 48 MHz 54 MHz NOTEThese levels were standardized here and subsequently used by Uni-Dir-PICS-I01-030903 which became codified by reference in FCC regulations. See 47 C.F.R. 15.123(c)(1) and 47 C.F.R 15.38. b) Desired TV visual carrier: -49 dBm (0dBmV) NOTEThis level is the minimum allowed by FCC

20、47 C.F.R. Part 76.605. 4 Measurement Procedure for Immunity of TV Tuners to Harmonically Generated Interference 4.1 Objective The objective of this measurement procedure is to determine the level of interfering signals that generate harmonics in the tuner or leak through the tuner, causing visible i

21、nterference in a nominal desired signal at the intermediate frequency (IF) output of a tuner under test. The interfering input signal is referenced to a 75 ohm load, and the tuner is then substituted for this load. 4.2 Measurement of Interference Immunity CEA-544-C R-2014 2 The sensitivity of the NT

22、SC spectrum to visible interferers is not flat. The highest sensitivity is near 0.5 MHz and again at 3.5 MHz relative to the video carrier. Sensitivity between these points is reduced by up to 15 dB. Thus, designing tests which hit these sensitive points is the most relevant. Cable systems have data

23、 signals from set-top boxes below 42 MHz. These signals can be as high as 60 dBmV to assure reliable data transfer to the head end. The mechanisms in receivers that create interference from signals below channel 2 include harmonic generation in a receivers tuner. For example, the second harmonic of

24、a signal at 28 MHz may beat with the channel 2 video carrier at 55.25 MHz to cause a visible interference pattern at 0.75 MHz. The standard test defined here measures the immunity of receivers to produce spurious responses in the desired channels bandpass that could result in a visible interference

25、or other impairment resulting from undesired signals in the frequency range of 5 to 54 MHz. The test set up makes several simplifying assumptions: a) There is only one significant interfering signal available at a time, b) There is only one modulated desired signal available, c) The interfering sign

26、al is a single frequency rather than a modulated signal. 4.3 Procedure 4.3.1 Equipment List The following list of equipment is required to make the measurements listed in CEA-544-C: a) 1 NTSC pattern generator b) 1 NTSC Modulator c) 1 Signal generator for interfering signal (unmodulated). d) 2 50 to

27、 75 ohm minimum loss resistive pads. e) 1 Spectrum Analyzer f) 1 75 ohm step attenuator g) 1 Combiner. h) 1 Low Pass Filter (ex. CMTS Diplex filter ViewSonics vsredp-40) i) Video Measurement Device (ex.VM700) 4.3.2 Equipment Diagram Low-Pass FilterVideo Measurement DeviceCombinerNTSC Signal Generato

28、r5 60 MHz Signal GeneratorSpectrum AnalyzerDUTNTSC Modulator75/50 PAD75/50 PAD75 Step AttenuatorFigure 1 Measurement Equipment Diagram 4.4 Measurement Procedure Assemble the equipment as shown in Figure 1. This generic setup will enable the operator to inject a known interferer and measure its effec

29、t on the device under test. The spectrum analyzer is used to set the levels of the input signals. The video measurement device is used to measure the video output of the receiver to determine the degree of interference. 4.4.1 Calibrate the Desired Signal CEA-544-C R-2014 3 The intent of this procedu

30、re is to create a known signal level for use in the interference measurement. Calibration is performed with the combiner output connected to the Spectrum analyzer. 1. Set NTSC video generator to Color bar and feed to the channel 2 NTSC modulator. 2. The channel 2 modulator usually creates a high lev

31、el output (0 dBm). Reduce the signal level via the 75 ohm step attenuator to -49 dBm as measured on the spectrum analyzer. 4.4.2 Calibrate the Undesired Signal The intent of this procedure is to create a precise level of interference for use in the interference measurement. First, the interfering si

32、gnal level is set with the aid of the Spectrum analyzer. Second, the result of a known threshold interferer is recorded from the video measurement device. Two points in the video spectrum may be calibrated. One is above the video carrier and the other is above the color carrier. 1. Remove the low pa

33、ss filter to allow an in-band signal. 2. Using a calibrated RF signal generator (ex. HP8648C) to create an unmodulated carrier at 56MHz Use a 50/75 ohm minimum loss pad on the RF output. 3. Using the internal attenuator of the signal generator set the power to -49 dBm as measured with the spectrum a

34、nalyzer 4. On the RF generator PRESS reference power zero then add 53dB of attenuation. This is the limit of visibility of an undesired signal in the NTSC spectrum. 5. Connect the desired and undesired RF signals to the device under test. 6. Feed the video output from the receiver to a video measure

35、ment device (ex. Tektronix VM700). 7. Measure the noise at 0.75 MHz (video measurement device in noise / spectrum analyzer mode) and record the amplitude for future reference. (The interference level is expected to be measured as approximately -37dB relative to one volt of video.) 8. Repeat the abov

36、e steps for an IF rejection test using 59 MHz in step 2 and 3.75 MHz in step 7. 4.4.3 Interference Measurement Harmonic interference is created by presenting a carrier to the tuner at a level sufficient to cause harmonics. The degree of interference is measured in the output video spectrum. The resu

37、ltant interference is compared to the calibration interferer level from Section 4.4.2. Tuner IF bleedthrough is measured by presenting a carrier to the tuner. The frequency of the carrier must fall within the IF passband of the Device Under Test. Again, the degree of interference is measured in the

38、output video spectrum and compared to the calibration interferer level from Section 4.4.2. 1. Reinsert the low pass filter. 2. Set the interfering carrier frequency to 28 MHz (42 MHz for IF rejection) 3. Set the interfering carrier amplitude to the limit stated in section 3a. A -7 dBm signal would b

39、e 42 dB above the reference power level set in section 4.4.2 step 4. An additional offset (approximately 0.4 dB) is necessary to compensate for the low pass filter loss. 4. View the video spectrum with the video measurement device at 0.75 MHz. 5. Repeat the above steps for IF bleed through with an i

40、nterferer of 42 MHz for step 2 and 3.75 MHz for step 4. Distortion or non linearity in the tuners RF front end will cause a resultant spike on the video measurement device at 0.75 MHz (3.75 MHz for alternate tests). If this spike exceeds the level previously recorded in section 4.4.1, step 7(step 8)

41、, the device does not meet the requirements. CEA-544-C R-2014 4 Similar to the above procedure, the rest of the frequency and limits defined in Section 3a may be tested. Frequencies below 30 MHz should include the low pass filter so that generator created harmonics are not presented to the tuner inp

42、ut. Frequencies above 30 MHz should be tested on channel 2 without the low pass filter to assure that the filter is not attenuating the interferer. Interference originates from at least two sources: (1) Out of band signals (OOB) from 5-42 MHz appear in the first amplifier and (2) the mixer creates s

43、econd order harmonic distortion. An example of out of band signals might be when a 42 MHz signal leaks into a pre-selector and mixer, coupling through the IF Filter. This creates a product in the video at 3.75 MHz on all channels when the IF picture carrier is at 45.75 MHz. An example of a mixer cre

44、ating second order harmonic distortion might be when a 28 MHz signal creates a 56 MHz product in the receivers first stage. This 56 MHz product causes another beat product in the video at 0.75 MHz when observing Channel 2 at 55.25 MHz. If a receiver has a 5 MHz center frequency IF with the picture c

45、arrier at 6.75 MHz an interfering signal at 6 MHz creates a beat product at 0.75 MHz in the video signal. 4.5 Setup of Spectrum Analyzer An example of typical spectrum analyzer control settings is indicated in Table 1. R Section Resolution Bandwidth 2 MHz Scan Bandwidth 0.5 MHz/division Input Attenu

46、ator 10 dB Frequency 55.25 and 56 MHz I Section Scan Time 50 milliseconds Log. Ref. Level -20 dBm Video Filter 3MHz Table 1 Example of Typical Spectrum Analyzer Control Settings 4.6 Repeat at Other Operating Conditions Interference susceptibility can vary with tuner operating conditions, e.g., AGC.

47、Measurements should be made at +6 dBmV and +15 dBmV desired signal level. If necessary, explore in the vicinity of the +6 dBmV point to find the worst AGC level. CEA Document Improvement Proposal If in the review or use of this document a potential change is made evident for safety, health or technical reasons, please email your reason/rationale for the recommended change to standardsce.org. Consumer Electronics Association Technology & Standards Department 1919 S Eads Street, Arlington, VA 22202 FAX: (703) 907-7693 standardsce.org