1、CCIR RECMN*O3 92 W 4855212 0520306 343 Rec. 803 103 RECOMMENDATION 803 THE AVOIDANCE OF INTERFERENCE GENERATED BY DIGITAL TELEVISION STUDIO EQUIPMENT (Question 25/1 I) The CCIR, 1992) considering that equipment built to operate on the CCIR Recommendation 601 digital video standard utilizes a samplin
2、g frequency of 13.5 MHz, of which the ninth harmonic coincides exactly with an international distress frequency of 121.5 MW*; distress use; processing is required for reliable detection; that 243 MHz*, or the eighteenth harmonic of the sampling frequency, is also reserved for international that thes
3、e distress signais are usually detected by aircraft or satellite receivers, and sophisticated signal that No. 964 of the Radio Regulations prohibits any harmful interference on the emergency frequencies. recommends that the design, construction and operation of digital equipment must take into consi
4、deration the need to eliminate harmful interference, as a high priority, and the following methods of measurement and limits of radiated interference field strengths should be used. 1. Measurement methods CISPR Publications 16 and 22 are recommended as detailed specifications and procedures for meau
5、ring electromagnetic radiation. When measuring the radiation from a particular item of equipment, the real-life operational conditions of the equipment must be adhered to as far as possible. In particular, all external connections must be present. 2. Acceptable levels of radiation Table 1. The elect
6、romagnetic radiation limits for Class A equipment* should conform with the limits* given in TABLE 1 Limits of radiated interference field strength at a test distance of 30 m for Class A equipment Frequency range Quasi-peak limits I (dB(pV/m) 30 to 230 230 to 1 O00 30 31 These values correspond to th
7、ose in CISPR Publication 22. * The international distress frequencies, 121.5 MHz and 243 MHz are used by Emergency Location Transmitters (ELT) in ihr aeronautical service and emergency position indicating radio beacons (EPIRB) in the marins service. * Non-domestic low voltage equipment. Some adminis
8、trations specify the limits given in Annex 1. * CCIR RECMN*BOI 72 E Li855212 0520107 28T 9 104 Rec. 803 3, Circuit design Annex 2 gives advice on circuit design mctliods. 4. Measurement of radiated interference levels Some information about measurements carried out is given in Annex 3. ANNEX 1 TABLE
9、 2 Llmlts of spurlous cmlsslons (CSA Class A) Maximum field strength at 30 m (dBpV/m) Frequency Maximum field strength at 30 m (WZ) WWW) 30 to 88 88 to 216 216 to loo0 30 34 37 ANNEX 2 Circult design methods The following nrrnngcment may be employed in circuit beard design: - - - - - circuit board t
10、o be partitioned by logic speed, frequency and function; impeance matching for high-sped logic devices, e.g. balancecl ECL circuit; use of multi-layer printed circuit boards with power and ground distribution planes; anaiogue and digital power busses to bc isolated from each other; decoupling capaci
11、tors with low effective series resistancc and inductance to be placed close to IC power pins; decoupling capacitor to be employed at the point where the power supply enters the board; surface mounted components to be used where practical. - - The following techniques may be employed for the minimiza
12、tion of electromagnetic radiation from equipment: - - - - - - use of RF-screened chassis; - use of connectors that are shielded and earthed to the equipment chassis; shielding ,and comparlmentalizing of components or sub-assemblies; shielding and minimizing the length of internal wiring; bringing ea
13、rths and shields to a common point; use of multi-layer boards with ground-planes for extender modules; use of “twist-In-flat“ and shielded cable, as weil as specially designed circular cablcs. CCIR RECMN*803 92 W 4855232 0520308 336 Rec. 803 ANNEX 3 Measurements of radiated interference levels 1 o5
14、Measurements of the levels of radiated signals at 121.5 MHz for a prototype digital PAL-RGBIYCRCB decoder based on Recommendation 601 have been conducted in Australia using a measurement tecbnique conforming with CISPR Publication 22. At a distance of 30 m from the decoder field strength levels of u
15、p to 46 dB(pV/m) were measured. With cables removed levels of 37 dB(pV/m) were measured. Similar measurements were carried out in the United Kingdom again on experimental processing equipment conforming to Recommendation 601, and adhering closely to the measurement technique outlined in CISPR Public
16、ation 22 in order to ensure repeatable results. The equipment under test was mounted on a remotely controlled turntable, and the measuring antenna was adjustable in height and polarization so that worst case measurements could be obtained, field strength levels (referred to 30 m) of up to 39 dB(pV/m
17、) were measured. However, when the equipment was enclosed in a wire mesh cage a value of 24 dB(pV/m) (referred to 30 m) was obtained. These measurements on prototype equipment demonstrate that a potential problem exists. Careful atten tion needs to be paid to the electromagnetic compatibility of equ
18、ipment based on Recommendation 601 in design, manufacture and use. In Japan, measurements of the radiation from commercially produced digital video equipment having a sampling frequency of approximately 14.3 MHz have been conducted. While this equipment does not conform to Recommendation 601 the lev
19、els of measured ninth harmonic (128.7 MHz) radiation may provide a useful guide to the levels that could be obtained from commercially produced equipment conforming with Recommendation 601. The level of the ninth harmonic radiation measured was 22 dBV/m), referred to 30 m. Results carried out at an
20、experimental digital television studio in France gave mean field strengths which at 30 m would amount to between 29 and 37.8 dBV/m). If an additional attenuation of at least 20 dB due to the concrete construction of the studio is taken into account, the resultant field strength would certainly be below the appropriate CISPR hit which is 30 dB(pV/m) at 30 m. 9!?Qi . , : . .
