Randolph Telecom

Publications

  • Introduction to Lightning and AC Power Fault Surge Protection for Telecom Signaling Cables PDF This paper was presented at the 2012 Symposium of the IEEE Product Safety Engineering Society, where it received the Best Paper award. The paper provides an introduction to the types of lightning surges and AC power fault surges that commonly affect the signaling cables of telecom network infrastructure and terminal equipment. Discussion is limited to twisted-pair copper lines such as telephone tip/ring cables and Ethernet cables. Surge types addressed include induced surges caused by nearby lightning strikes, induced AC voltages caused by fault conditions in adjacent AC power cables, and events caused by direct contact with AC power mains. Some general guidelines are provided for evaluating the surge tolerance of a given design based on an analysis of the applied surge and the available paths for surge currents to flow. This type of analysis will often identify potential weaknesses based strictly on a review of the proposed design, prior to performing any actual surge tests.
  • Lightning Surge Damage to Ethernet and POTS Ports Connected to Inside Wiring PDF This paper was presented at the 2014 IEEE Symposium on Product Compliance Engineering, where it received the Best Paper award. The paper discusses lightning damage to Ethernet and POTS ports connected to cables routed entirely within the same building. Manufacturers in both the USA and Japan have reported surprisingly high rates of lightning damage to ports on optical network terminals used for fiber-to-the-home delivery of telecom services. Similar damage has been reported on VOIP PBXs. While there are three known mechanisms by which lightning can couple onto inside wiring, their occurrence is believed to be statistically infrequent. The paper discusses these three known mechanisms as well as three new theories that are currently under study. All three of the new theories are based on the notion that surges on the AC mains are being coupled onto inside wiring communication cables. While research on these new theories continues, some guidelines are provided for manufacturers who wish to implement enhanced surge protection on Ethernet and POTS ports connected to inside wiring.
  • AN-1: Why Hire a Technical Consultant? PDF Joe summarizes his perspective on the circumstances where it is appropriate to bring in an outside technical consultant. He describes various situations where it is cost effective to hire a technical consultant, and describes the attributes you should look for in a technical consultant.
  • AN-2: Ten Key Considerations Before You Start Your DAA or FXO Phone Line Interface Design PDF The basic functions of a DAA (Data Access Arrangement) or FXO (Foreign Exchange Office) phone line interface circuit are essentially identical, but the specific performance requirements that must be met will differ depending on the application. This application note describes ten key questions to answer before you commit to a particular implementation strategy.
  • AN-3: Seven Key Considerations Before You Start Your SLIC or FXS Phone Line Interface Design PDF The basic functions of a SLIC (Subscriber Loop Interface Circuit) or FXS (Foreign Exchange Subscriber) phone line interface are essentially identical, but the specific performance requirements that must be met will differ depending on the application. This application note describes seven key questions to answer before you commit to a particular implementation.
  • AN-4: Low Cost Telephone Line Interface (DAA, FXO) PDF This is a reprint of an application note that was originally published as Midcom TN #98. It describes a very basic, rugged, and inexpensive transformer-based phone line interface circuit. Included is a schematic diagram, parts list, and cost estimate.
  • AN-5: Transformer-Based Phone Line Interfaces (DAA, FXO), Rev1 PDF This is an expanded version of AN-4. A second circuit has been added that provides some enhancements that may be desirable for certain applications. Also included is a brief review of how transformer-based DAA and FXO circuits compare to silicon DAA and FXO circuits.
  • AN-6: Common Mistakes in Lightning Protection of Phone Line Interface Circuits, Rev1 PDF This application note provides a brief review of how lightning surges appear on phone lines, and explains the terminology that is typically used in discussing lightning protection of phone line interfaces. With this background, several common mistakes in the design of phone line lightning protection circuits are described.

Future Topics
Following is a list of additional topics that Joe plans to write about as time permits. Feel free to email Joe with suggestions for other topics that you would like to see addressed.

  • POTS telephony FAQ
  • FCC Part 68 for Novices
  • Getting Your Telephone Product Approved in Europe
  • Getting Your Telephone Product Approved Worldwide
  • Testing Voice Telephony Products for Compliance With Europe's EN55024 EMC Immunity Requirements
  • Power Cross Tests in UL 60950 and Telcordia GR-1089 (also ITU K.21, ITU K.22, and Brazil)
  • Noise Sources in Voice Telephony Circuits
  • Balance and Hum in FXO and FXS Interfaces
  • Echo in VOIP Systems
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