CEA-544-B-2004.pdf
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1、 CEA Standard Low Frequency Immunity of Tuners in a Cable System CEA-544-B November 2004 Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:47:08 MDTNo reproduction or networking permitt
2、ed without license from IHS -,-,- NOTICE CEA Standards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purc
3、haser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards, Bulletins and other technical publications shall not in any respect preclude any member or nonmember of CEA from manufacturing or selling products not conforming to such Stand
4、ards, Bulletins or other technical publications, nor shall the existence of such Standards, Bulletins and other technical publications preclude their voluntary use by those other than CEA members, whether the standard is to be used either domestically or internationally. Standards, Bulletins and oth
5、er technical publications are adopted by CEA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, CEA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard, Bulletin or other techni
6、cal publication. This CEA Standard is considered to have International Standardization implication, but the International Electrotechnical Commission activity has not progressed to the point where a valid comparison between the CEA Standard and the IEC document can be made. This Standard does not pu
7、rport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. (From Projec
8、t Number 2126, formulated under the cognizance of the CEA R8 Cable Compatibility Committee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2002 Technology minimum attenuation at interfering signal harmonics greater than 90 dB. e) 1 Interfering frequency band-reject filter with minimum attenuation of
9、 100 dB at undesired frequency. f) 2 50 to 75 ohm impedance transformers. (A typical transformer has approximately 0.1 dB power loss.) g) 2 75 ohm 6 dB pads. h) 1 Spectrum Analyzer i) 1 50 ohm 6 dB pad. j) 1 Coaxial switch 40 dB isolation minimum. The following equipment is optional: k) 2 Step atten
10、uators. 4.3.2 Equipment Diagram See Figure 3. 4.4 Calibration of the Interference Signal Path, 27 MHz Example Check for undesired harmonic content of the 27 MHz source with the following procedure: a) Arrange the equipment as shown in Figure 1. Adjust the level of the 27 MHz signal to give a reading
11、 of the input signal to the analyzer of + 10 dBm, with the appropriate RF attenuation setting in the analyzer. This corresponds to a level of 16 dBm (1.4 V at 50 ohm) at the output of the signal source, which would be 10 dBm (0.86 V at 75 ohm) at the spectrum analyzer input. b) Insert a 27 MHz band-
12、reject filter into the signal path after the 75/50 ohm impedance transformer, as shown in Figure 2. This minimizes harmonic distortion in the analyzer. The reason for the 50 ohm-6 dB pad after the power amplifier is to minimize reflections on the line when the 27 MHz band-reject filter is inserted.
13、c) With the RF attenuation in the spectrum analyzer removed, measure the power level of the 54 MHz second harmonic as shown in Figure 2. It should be at or below 100 dBm. The analyzer is now at the +10 dBm point of the circuit, referenced to the fundamental. Thus, any spurious 54 MHz harmonic is 110
14、 dB or more below the 27 MHz fundamental. 1 NOTEThe use of the amplifier is dependent on the signal generator output in relation to the undesired signal level required. Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Ber
15、nie Not for Resale, 03/30/2007 21:47:08 MDTNo reproduction or networking permitted without license from IHS -,-,- CEA-544-B 3 SIGNAL SOURCE 6 dB PAD LOW-PASS FILTER IMPEDANCE TRANSFORMER 50 TO 75 OHMS COAXIAL SWITCH INTERNAL ATTENUATOR SPECTRUM ANALYZER 27 MHz, 16dBm (40mW or 1.4V) at 50 ohms 27 MHz
16、, 10dBm IMPEDANCE TRANSFORMER 75 TO 50 OHMS Figure 1 Interference Signal Path, 27 MHz Example Figure 2 Second Harmonic Measurement, 27 MHz Example SIGNAL SOURCE 6 dB PAD LOW-PASS FILTER IMPEDANCE TRANSFORMER 50 TO 75 OHMS COAXIAL SWITCH SPECTRUM ANALYZER 27 MHz, 16dBm (40mW or 1.4V) at 50 ohms 27 MH
17、z, 10dBm IMPEDANCE TRANSFORMER 75 TO 50 OHMS 27 MHz BAND- REJECT FILTER 54 MHz, -100dBm Maximum Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:47:08 MDTNo reproduction or networking
18、permitted without license from IHS -,-,- CEA-544-B 4 SIGNAL GENERATOR OPTIONAL AMPLIFIER LOW-PASS FILTER IMPEDANCE TRANSFORMER 50 TO 75 OHMS COAXIAL SWITCH SPECTRUM ANALYZER Undesired Source (e.g., 27.405 MHz) 6 dB PAD 75 OHMS TUNER Impedance Matching as needed Shown in signal path to raise level av
19、ailable at tumer. SIGNAL GENERATOR IMPEDANCE TRANSFORMER 50 TO 75 OHMS Desired Source (TV Channel 2, 55.25 MHz) P2 P1 A RF IF POWER SUPPLY 53dB DU (In this procedure, the desired and undesired, or interfering, signals do not appear simultaneously at the IF output.) Notes: 1. Measure Gain A-B from Po
20、int A to Point B with spectrum analyzer, with Point B terminated in 75 ohms. 2. Step attenuators may be inserted at P1 and P2 to improve accuracy and repeatability. 3. P Desired = P2 (dBm) - 6 dB P Undesired = P1 (dBm) + Gain A-B (dBm) B Figure 3 Equipment Diagram, 27 MHz Example 4.5 Setup of Spectr
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