ANSI SCTE 78-2017 pdf free download – Test Method for Transfer Impedance.
1. Introduction
1.1. Executive Summary
Transfer impedance is a measure of shielding effectiveness.This procedure provides instructions forperforming the measurement on flexible coaxial drop cables.
1.2. Scope
This procedure is for the measurement of transfer impedance of coaxial drop cables from 5 MHz to themaximum specified frequency using a terminated tri-axial test fixture.
1.3. Benefits
Using this procedure, the transfer impedance of a cable can be characterized and used to determine itsshielding effectiveness.Lower transfer impedance means better shielding and less signal ingress oregress.
1.4. lntended Audience
This is a laboratory measurement used primarily by development engineers for the improvement ofcoaxial drop cable shields.
2.Normative References
The following documents contain provisions,which, through reference in this text, constitute provisionsof this document. At the time of Subcommittee approval, the editions indicated were valid.All documentsare 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 arereminded 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 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 whencomplying 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
• No informative references are applicable.
6. Equipment
• Terminated Tri-axial Test Fixture (See Figure 6.)
• Signal Source (Swept Frequency Oscillator)
• Detector, Display
• (Note: A spectrum analyzer with a tracking generator may be used or a network analyzer with a signal source may be used for the signal source, detector and display.)
• Termination loads
• Attenuators
• Optional Power Attenuators (used in conjunction with the optional RF Amplifier)
• Optional RF Power Amplifier
• Coaxial “T” (For velocity of propagation measurements)
7. Calibration The frequency of the signal source and loss of the attenuators shall conform to appropriate laboratory standards including traceability to recognized measurement standards.
8. Specimen Preparation & Installation Measure the cable so that it will be long enough to fit through the chamber and toroids and connect to the fittings at the end of the test fixture. Carefully remove two small “windows” of jacket from the specimen. Each window should be approximately 0.5 to 1 cm (3/16 to 3/8 inch) long and approximately 0.5 cm (3/16 inch) wide. The windows should be placed 1.00 meter (39.37 inches) apart and each 0.5 meter (19.69 inches) from the center of the sample so that the chamber probes, which are spaced 1 meter apart, can make electrical contact with the outer conductor of the specimen. Care must be taken not to damage the outer conductor when cutting through the jacket especially if the outer most layer of the outer conductor is a thin aluminum tape. See Figure 1.
Install the specimen through the terminated tri-axial test fixture. See Figure 6. Install the appropriate connectors at the ends of the specimen. Insert the probes into the chamber to make electrical contact with the outer conductor of the specimen. Care should be taken not to damage the shield of the specimen especially if the outer conductor is a thin aluminum tape. An electrical continuity test can be performed to assure that the probes are making contact with the outer conductor of the specimen.ANSI SCTE 78 pdf download