ANSI SCTE 249-2018 pdf free download.Test Method Common Mode Disturbance
1.1. Executive Summary
Common mode disturbance is generated by power electronics in all active devices. These are typically in the frequency range from 150 kHz to 30 MHz, though higher frequency disturbances are possible. These disturbances can be radiated and cause interference with wireless signals, or can become differential mode and be coupled into the upstream signal path of the cable plant, cause degradations to upstream signal-to-noise.
1.2. Scope
The purpose of this test is to determine the common mode disturbance generated by power electronics in active CPE equipment. Since conducted disturbances on the AC port is already a part of FCC testing requirements, this method focuses on measurements of the common mode disturbance on the coaxial port. Common mode disturbance from stand-alone power supplies are conducted through a common ground plane on the CPE device to the outer conductor of the coaxial port. Therefore stand-alone power supplies are also within the scope of this standard.
1.3. Benefits
Devices that exhibit excessive amount of common mode disturbance performance can cause potential
problems such as:
• AM interference – common mode disturbances in the frequency range from 500 kHz to 1.5 MHz
can radiate into the air and cause interference to AM radio.
• CATV upstream SNR (MER) – abrupt impedance changes (such as bad contact from a loose
connector) causes the common mode disturbance to become differential mode, which is coupled
into the coaxial cable. Common mode disturbance from 5 MHz to 42 MHz affects SNR (MER)
of existing CATV upstream signals, causing dropped connections and excessive bit error ratio on
a per node basis. (Note: This standard extends testing to 200 MHz to take into account higher
frequency splits necessitated by DOCSIS 3.1 and Full Duplex DOCSIS.)Ensuring that all active devices are tested according to this standard successfully mitigates the problems listed above, which in turns improves the resiliency of the DOCSIS network.
1.4. Intended Audience
The intended audience for this document are development engineers, quality assurance engineers, product managers, and technical operations engineers from both manufacturers and operators. Technicians and installers can benefit from this document as well to help troubleshoot issues in the field.
1.5. Areas for Further Investigation or to be Added in Future Versions
Areas to be investigated or added in future versions include:
• Alternative to the CDN, such as current clamps
• Use of programmable AC supplies instead of LISN to allow for the following test cases:
o Low voltage
o High voltage
o Harmonics
2. Normative References
The following documents contain provisions, which, through reference in this text, constitute provisions of this document. At the time of Subcommittee approval, the editions indicated were valid. All documents are subject to revision; and while parties to any agreement based on this document are encouraged to investigate the possibility of applying the most recent editions of the documents listed below, they are reminded that newer editions of those documents might not be compatible with the referenced version.
2.1. SCTE References
• No normative references are applicable.
2.2. Standards from Other Organizations
• CISPR 22:2008 (EN55022:2010)
• CISPR 16-1-1
• CISPR 16-1-2
• IEC 61000-4-6
2.3. Published Materials
• No informative references are applicable.
3. Informative References
The following documents might provide valuable information to the reader but are not required when complying with this document.
3.1. SCTE References
• No informative references are applicable.
3.2. Standards from Other Organizations
• No informative references are applicable.
3.3. Published Materials
• Y. P. Chan, B. M. H. Pong, N. K. Poon and J. C. P. Liu, “Common-mode noise cancellation in
switching-mode power supplies using an equipotential transformer modeling technique”, IEEE
Tran. Electromagnetic Compatibility, vol. 54, no. 3, pp. 594-602, 2012
