ANSI SCTE 48-3-2018 pdf free download.Test Procedure for Measuring Shielding Effectiveness of Coaxial Cable and Connectors Using the GTEM Cell
1.1. Executive Summary
The shielding attributes of components in a CATV system are critical to system performance. Ingress
and egress issues can have detrimental effects on the overall performance of the system from both
regulatory and quality perspectives.
Ingress issues can cause problems with television picture quality, and the effective transfer of data by allowing spurious signal into the system.
Egress issues can allow signals captured in the system to leak out and possibly interfere with wireless
communications which utilize the same frequencies as those signals being leaked from the system.
It is the goal of this document to address the coaxial cables and connectors in the system, and how to properly gauge their performance in this critical area.
1.2. Scope
This document details the procedure for measuring the Shielding Effectiveness (S.E.) of coaxial cable
and connectors using the Gigahertz Transverse ElectroMagnetic (GTEM) cell. More particularly, this
procedure applies to measuring the S.E. of 75 Ohm braided coaxial drop cables and connectors
presently used within the broadband communications industry. S.E. measurements can be performed
with or without the affixing coaxial connectors removed from the measurement.
1.3. Benefits
This procedure exists in order to provide a standard method of testing between laboratories
performing Shielding Effectiveness tests. When utilized this procedure helps to ensure confidence in
results when published.
1.4. Areas for Further Investigation or to be Added in Future Versions
Future revisions of this document may build upon the work started here by increasing the
understanding of:
• Variability of data between GTEM Cell systems with varied “uniform field” sizes.
• The affects of location differences between bare wire and shielded samples within the GTEM
cell.
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 SCTE references are applicable.
2.2. Standards from Other Organizations
• No normative references are applicable.
2.3. Published Materials
• No normative 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
• IEC 61000-4-20 2nd Edition, August 1, 2010. Electromagnetic compatibility (EMC) – Part 4-20:
Testing and measurement techniques – Emission and immunity testing in transverse
electromagnetic (TEM) waveguides.
3.3. Published Materials
• A GTEM BEST PRACTICE GUIDE – APPLYING IEC 61000-4-20, TO THE USE OF GTEM
CELLS. A. Nothofer, M.J. Alexander, National Physical Laboratory, Teddington, UK, D. Bozec,
D. Welsh, L. Dawson, L. McCormack, A.C. Marvin, University of York, Heslington,
UK(Principal contact: nothofer@ieee.org)
• http://ieeexplore.ieee.org/search/searchresult.jsp?newsearch=true&queryText=GTEM
Multiple helpful documents
6.3. Calibration and Equipment Preparation
Data points – The number of measurement samples taken is at the discretion of the Engineer
performing the test, however, as a minimum requirement there will be at least one sample point
every 5 MHz (i.e. 5, 10, 15, …… upper frequency limit).
When testing frequencies above 1GHz, it may be necessary to use multiple amplifiers to cover
the entire range. The following items should be considered when using multiple amplifiers.
• Safety consideration must be taken into account if manually switching between
amplifiers, and the amplifier outputs must be off before switching them.
• When using data collecting and control software for a spectrum analyzer, and manually
switching amplifiers there should be a pause feature to stop the sweep at the correct
frequency to switch amps and then continue sweep once correct amp is in place.
• Be sure to verify that all supporting equipment, i.e. pre amp, attenuators etc. are
correctly chosen to cover the entire frequency range in question.
RF power level – As this test is designed as a comparison of shielded vs unshielded cable, an
exact field strength is not stated. It is necessary however to have enough energy in the GTEM
as is necessary to achieve sufficient dynamic range for the measurements being made.
Attenuator characterization – Any attenuators that may be inserted or removed from the
measurement during the measurement process shall be characterized and data stored for later
use during S.E. calculations.
