Articles and FAQs
- 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) 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 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