• Telephone technology page

    • Business telephone systems
    • Computer telephony
    • Design notes on telephone circuits
    • Do it yourself telephone installations
    • Fax
    • General info
    • How telephone network works
    • Telephone info specific to Finland
    • Telephone equipment regulations
    • Signaling and coding
    • Radio interference
    • Telephone circuits
    • Telephone hacking
    • Telephone history

    General info

    • Coherent Communications Articles - full duplex and echo control
    • Copper Subscriber Loop - overview
    • Counterintelligence and Counterterrorism WWW Page - information about surveillance and countersurveillance
    • International Callback - a simple service based on a simple idea, which is to provide overseas customers with US dial tone, through which they can originate calls at much lower rates
    • International Dialling Codes - country codes and dialling prefixes
    • Telecommunication Tidbits - links and information articles
    • The Telecom Corner!
    • Traffic calculation sheets - Excel and Lotus format spreadsheets, zipped file, from Gene's Phone Home Page and Telecommunications Links
    • World Wide Phone Guide - What you need to hook up your modem just about anywhere!

    Business telephone systems

    • All about the Ma Bell circuit - termination, wiring, and terminal hardware most commonly used in the Bell system
    • Doing An End Run Around The Local Telephone Company - by using Point To Point Wireless Service
    • Microphone Performance Impact on Speakerphone Applications
    • Modem connection - Tips on how to connect the modem in all circumstances, very useful tips for business travellers
    • Pacific Telephony Design Tutorials and Articles - a good collection of tutorials

    Telephone history

    • Antique Telephone Collector's News
    • Bell System Home Page - schematics, drawings, tables, photos, and other information pertaining to telephones produced by Western Electric for the Bell System prior to 1984
    • Cyber Telephone Museum - An Exhibit of Common & Rare Antique Telephones
    • Historic Telephony - telephony history and old telephones
    • Telephony history pages from Mike Sandman - old telephone related ads and articles
    • The Strowger Telecomms Page - information about old electromechanical telephone exchanges
    • Tribute to the Telephone - history, schematics, trivia, photos, links and other telephony related pages

    How telephone network works

    • 2 Wire / 4 Wire Hybrid Coupler - where electronic amplification is required for long distance transmission, hybrid coupler circuits are used to separate the two signals so that unidirectional (4 wire) amplifiers may be used, check also Hybrid Coupler Example
    • Disassembly Of A Touch-tone Phone - what is inside modern telephone
    • EE 816 Telephony - course notes on telephone systems and transmission lines, includes demonstration pictures
    • How telephone recording adapters work
    • Lifting Ma Bell's Cloak Of Secrecy - A New Look At Basic Telephone Systems, zipped file containing Phrack Magazine issue 24
    • Loop current technical bulletin - what are the problems when the loop current is too low or high
    • Phone line audio characteristics - article from Radio Guide Magazine
    • Phone System Tutorial I - read also part II
    • Telephone Line Indicator design - information on the characteristics of telephone lines
    • Telephone line audio interface circuits - telephone hybrid circuits described and more
    • Telephone Signals and Circuit Conditions - as used in the USA and Canadian Telephone System
    • Two and Four Wire Transmission - and how hybrid transformer can convert between them
    • Understanding telephones - technical introduction to how telephones work, also archived at http://massis.lcs.mit.edu/telecom-archives/archives/technical/how.phones.work
    • Voice Networking 101 - reference source for telephone technology information: basics, electrical characteristics, hybrid circuits, echo, signaling, PBX, voice digitalization and standards information

    Do it yourself telephone installations

    • Adding a Jack to an Existing Phone Line - step by step instructions for wiring used in USA
    • Adding a Second Line to Your Existing Phone Jacks - for wiring used in USA
    • An Introduction to Providing Your Own Telephone Wiring
    • Phone Man's Advice for Wiring Your Home Phone Lines
    • JACKS and PLUGS - Universal Service Order Codes to identify tariffed services and equipment
    • Telecom Tools - some of the most used telecom installer tools are also found in the average home tool kit
    • Telephone installation accessories manufacturers - connectors, cabling systems, tools and more
    • The Basics of Telephone Wiring
    • What do all the wire colors mean?

    Fax

    • comp.dcom.fax FAQ
    • comp.dcom.fax FAQs
    • Rockwell class 1 and 2 fax command information - fax modem commands
    • Solwise Guide to Computer Communications - includes fax standard table

    Computer telephony

    • Audio/Telephony Integration with AC '97
    • Direct Image - internet telephony information, info on software for doing it
    • How Do I Stop my Phones From Interrupting My Modem - telephone mini-FAQ
    • How to connect your computer modem to a hotel phone
    • Internet Telephony Showcase - tutorials and information on products
    • IP Telephony Gateways: Long Distance With a Local Touch - article from Data Communications magazine web site
    • Java Telephony API
    • Ken's CT-Page - starting point for Computer Telephony surfing
    • Pulver.com - information on voice over IP
    • Telecom Tutorials and Articles - In-depth Information on Telecommunications, Computer Telephony, Internet Telephony and More
    • Telephony Overview and Applications
    • The PBX Goes PC - voice-enabled modems and new software standards provide inroads to computer telephone integration
    • Tutorials and articles on Internet telephony - product test drives
    • Voice Over the Internet - Today it's a toy. Tomorrow it may be a crucial part of corporate telephony, article from Data Communications magazine September 1996
    • Wide Area Network Telephony - tutorial explains how to use internet telephony software coupled with peripherals to build a complete internet or intranet based telephone system
    • Writing Computer Telephony Software for Digital Telephone Networks

    Telephone info specific to Finland

    • Numbering of Telecommunications Networks
    • Telehallintokeskus - Telecommunications Administration Centre
    • Televerkkojen numerointiperiaatteet - telephone numbering in Finland, text in Finnish
    • Televiestintää koskevia lakiotteita teletoimintalaista ja rikoslaista - erityisesti säännösten rikkomisen seuraamuuksista kertovia kohtia
    • THK:n antamat määräykset - some telecom regulations in Finland
    • Usein kysyttyjä kysymyksiä teleliikenteestä ja -tekniikasta

    Telephone equipment regulations

    • The Telecommunications Terminal Equipment Directive - 91/263/EEC

    Signaling and coding

    Technical characteristics of tones for the telephone service are listed in ITU-T Recommendation Q.35 (1988). Infortunately that document is not freely available (can be ordered from ITU-T if you are willing to pay), so the information available in the following documents might be useful if you are looking for free information on telephone line signaling.

      Basic signaling

      • ITU-T E-Series Recommendations Excerpts - telephone information tones
      • Telephone ringing circuits - how to detect ringing and how to make phones ring
      • Telephone Signals and Circuit Conditions - as used in the USA and Canadian Telephone System
      • What is Ringer Equivalence?

      DTMF dialling

      • DTMF - Most Of What You Wanted To Know
      • DTMF coding and decoding using ADSP-2100 - pdf file with good text and some source code
      • DTMF Encoding and Decoding In C
      • Generating DTMF tones using computer soundcard
      • Touch-Tone Information - information on touch tone standards
      • Touch Tone WAV file generator - MS-DOS text-mode program for generating WAV files with DTMF sounds
      • WAV files of DTMF 0-9, dialtone and busysignal - zipped file from Gene's Telecommunications Links and Phone Home Pages

      Called ID

      • CallerID: The Next Advance in Telephone Services - introduction to called ID service concept
      • Caller ID circuits and information - information and circuits for different systems used USA and Finland
      • Caller ID Links - lots of links to web Sites related to caller ID
      • Caller Identification - What Standards are Involved?
      • Computer Caller ID FAQ
      • FCC Caller ID page - general info nad FAQ
      • Frequently Asked Questions About Caller-ID
      • Frequently Asked Questions About Caller-ID - from TELECOM Digest
      • FX602 Calling Line Identifier IC - for deconding called ID systems used in USA and UK, datasheet has example circuits
      • Guidelines for implementation caller ID service in Finland (GFI9702) - information about DTMF based caller ID system in use in Finland
      • Specs for UK caller ID - FSK system used in UK, info in zipped text file from Darrens Odds & Sods page
      • UK Caller ID FAQ homepage - information on setting caller ID system on PC

      Audio signal coding

      • Companding systems used in telephone PCM systems - A-law and my-law

      Misc

      • E-Series Recommendations Excerpts
      • How message waiting lights work - description of different message waiting light systems

    Radio interference

    • FCC Information Bulletin on Telephone Interference
    • FCC Interference Handbook - electronic version of FCC Interference to Home Electronic Entertainment Equipment Handbook
    • QST October 1992 Lab Notes on Telephone EMI - amateur radio telephone interference
    • Radio Interference to Telephones - articled how to avoid it
    • Radio signal suppression for telephone sets - Bell Systems Practices SECTION 500-150-100
    • RF Elimination Technical Bulletin
    • What to do if you hear radio communications on your telephone

    Telephone circuits

    The following telephone circuits are mainly ment to give ideas for your own desigs. Many of the circuits are quite propably do not meet your local telephone network terminal equipment specs (they vary from country to country) and are quite propably poorly designed (this applies as well to many circuits in books and hobby magazines). Connecting non-approved equipment to public telephone network is illegal in many countries. If you connect non-approved circuit which do not meet the specs to the public telephone network the telephone do not work properly with them and they also cause safety hazards.

    For information what is allowed to be connecte to telephone line the reader form USA should check FCC part 68 regulations and European reader should check NET4 (ETS 300 001) regulations. Good information on telephone equipment regulations can be found from Compliance Engineering Magazine website.

      Telephone equipments

      • Automatic Telephone Answering Unit
      • Handy Telephone Receiver - circuit for a medium performance handy electronic telephone receiver, suited for receiving incoming calls
      • Telephone Schematics for Western Electric Phones - Schematics, Drawings and Tables from Station Service Manual to view/download

      Audio Interfaces

      • Building and using phone patches - article from Ham Radio Magazine October 1985
      • Hands-Free Telephone - circuit to interface telephone handset connector to stereo heaphone and small microphone
      • How do I hook the Sound Blaster output to play over the phone line - zipped file
      • Playing a Mac through a standard telephone line - how to get sound from computer to telephone line
      • Phone "Hold" With Music
      • Simple Phone Tap - will record any conversation on any phone on same line, the circuit seems to be a bad design because it does not provide proper isolation and has too low DC impedance (can keep you line off-hook all the time)
      • Simple telephone test circuit - get telephone audio to mixer or send audio to telephone
      • Telephone Audio Interface - uses transformer and capacitor to isolate the line from external equipment, diode based surge protection on output
      • Telephone line audio interface circuits - telephone recording, telephone line to mixer and telephone hybrid circuits
      • Telephone Record Control - allows you to connect any tape recorder that has a mic and remote input to a phone line and automatically record both sides of a conversation when ever the phone is in use
      • Telephone Recorder - lets you record your phone conversations automatically
      • Telephone Tap - wire your telephone conversion to amplifier or tape recorder

      Busy indicators and related circuits

      • Phone Busy Indicator - simple busy indicator, does not meet regulations of many countries
      • Phone-In-Use indicator - simple design idea for indicator
      • Phone in use circuits - two designs
      • Phone In Use Indicator
      • Ringing Phone Light Flasher - when the phone rings light flashes, good ring detector example circuit
      • Telephone In-Use Indicator - A blinking LED lets others know when you are on-line!
      • Telephone In-Use Indicator - versions for LED indicator and relay output
      • Telephone Line Indicator design - information on the characteristics of telephone lines and circuit which connects to a telephone line and indicates whether or not the line is in use (seems to be quite good design)
      • Telephone privacy adapter - revents other telephones from hearing your call and disturbing your modem connection
      • Telephone recording switch - starts you tape recorder using a relay when you pick up telephone

      Caller ID and DTMF decoding circuits

      • Caller ID circuits and information - information and circuits for different systems used USA and Finland
      • Caller ID / DTMF Audio Decoder Sources & Links
      • Caller ID / DTMF audio decoder
      • Démodulate DTMF SSI 202 - DTMF demodulator circuit using SIS202, text in French
      • DTMF Generator/Decoder - tutorial with example circuit diagrams
      • DTMF Microphone - connects to PC game port
      • DTMF Products for you - DTMF decoder can be powered from a 9V battery or from your parallel printer, schematic and windows demo program, design by Schmidt Technologies
      • DTMF Tone Decoder with LCD Display - based on Basic Stamp microcontroller
      • UK Caller ID to PC serial port - decodes 1200 bps FSK signaling used in UK, zipped file, specs of UK caller ID coding are available at http://www.nitebeat.demon.co.uk/bt_clip.zip

      Dialler circuits

      • Un composeur automatique de numéro téléphonique - PC controlled DTMF dialler

      Test equipments

      • Bi-Directional Telephone Line Simulator - with Dialtone and Ring signals
      • Cut Phone Line Detector - can be used to alarm security system
      • Digital/Standard Phone Line Tester - make sure that the line is suitable for modem use and your PCMCIA does not damage if you plug it in
      • Digital/Standard Phone Line Tester - telephone line polarity and current detector

      Misc telephone accessories

      • Building a telephone answering system - laboratory report
      • Extension Phone Switcher - this circuit disables other telephones connected to the phone line whenever a telephone (eitherthe master or any extension phone) is in use
      • Ringing Phone Light Flasher - when the phone rings, lights connected to circuit flash
      • Telephone Call Counter - count and display the number of incoming calls received in the absence of the subscriber
      • Telephone Controlled Night Light - when the telephone rings, or when the handset is lifted, the night light is turned on and remains on while the conversation takes place
      • Telephone "distinctive ring" switcher - zipper demo file from Dunfield Devellopment System
      • Telephone Hold Button
      • Phone rang indicator light - will detect the ring signal, energize the relay which latches up, and the LED comes on and stays on till you push a switch
      • Telephone Recorder - lets you record your phone conversations automatically, notice that this circuit does not provide isolation between telephone line and the recorder
      • Telephone recording circuits - how they work and some example circuis

      Intercom circuits

      • Bi-Directional Telephone Line Simulator - works as complete intercom for two telephone, provides Dialtone and Ring signals
      • Cheap theatrical intercom system - intercom system made of old telephone
      • Connect two standard office telefax machines via 2 meter ham radio (at 2400 bps) - zipped file
      • Fax to Faxmodem interface circuit - can be also used as telephone intercom circuit or connecting two modems together
      • Use old telephones as intercom

      Surge protection

      • Telephone line surge protection - information and circuits
      • Telephone line surge protector circuit - also archived at ftp://nic.funet.fi/pub/doc/telecom/technical/lightning.surge.protect

      Telephone transmitters

      Telephone bugging is an illegal practice. The following circuits are for educational use. They are illagal in many countries.

      • FM Telephone Bug
      • FM Telephone Transmitter
      • Phone-bug - A simple transmitter that is powered from the phoneline, zipped file
      • Wireless Phone Jack - report what's inside it

      Misc telephone circuits

      • Phone Gadgets - conference call and hold button
      • Telephone-related ASCII Schematics - wide collection of telephone circuits

    Design notes on telephone circuits

      Signaling

      • DSP Solutions for Data/Facsimile Modems - application note from Texas Instruments, includes info on many usefula algoriths
      • MT8870 Datasheet - popular DTMF decoder IC from Mitel, datasheet in pdf format

      Line interfacing

      • 3750 V of Isolation Not Required at the Network Termination - technical note in pdf format from Midcom
      • dBm to RMS voltage chart - Microsoft Excel 4.0 format from Midcom Technical Notes
      • Gyrator circuit - simulate large coils electronically
      • Handy Line Interface Design Hints!
      • How to measure Total Harmonic Distortion (THD) of a transformer or other passive device - none page Word file from Midcom Technical Notes
      • Impedance measurements of telephone lines - two page technical note shows the impedances measured on the telephone line, for more information read the whole article in Microsoft Word format
      • Midcom Technical Note Technical Note Index - tech notes about telephone transformers
      • Optimum hybrid design - application note in pdf format
      • Optocouplers Isolate Modem Data Access Arrangement - Appnote from Siemens Semiconductors in pdf format
      • Overview of IEC 950 - EN 60950 (BABT), UL 1950 / CSA 950 - A Brief Overview of what it is and what is important when dealing with transformers in pdf format from Midcom Technical Notes
      • Return Loss Calculations - four page note explains how return loss can be determined and contains a MathCad analysis, an Excel spreadsheet analysis and a QuickBASIC program listing, zipped file from Midcom Technical Note library
      • Transformer Equivalent Circuit
      • Transformer Modeling Tips - technical note in pdf format from Midcom
      • Transformer Seminar Notes - companion to the seminar entitled "The Telecommunications Transformer: low-cost solution to product reliability and continuing regulatory compliance" by Dave LeVasseur, in Word 6.0 format, from Midcom, new version progressing, also available in zipped format
      • Two and Four Wire Transmission - how hybrid transformer is alligned
      • Wiring inside telephones

      Automatic terminal equipment

      • Phone Remote System - a telephone interface that allows the householder to give instructions to appliances from outside, application note from SGS-Thomson
      • Telephone & Answering System
      • The Official Small Switch Technology Site - information about telephone switch kit published in Circuit Cellar Ink magazine

      Telephone ringing

      • Telephone ringing circuits - how to detect ringing and how to make phones ring
      • Telephone Ring Generator
      • Telephone Ring Generator - will ring a telephone once every 10 seconds

      Telephone ICs

      • Voice Switched Speakerphone ICs (TEA1095) - pdf file

    Telephone hacking

    The following telephone hacking circuits are here only for educational purposes. Most of them don't work anymore and connecting them to telephone network is illegal.

    • 2600 Magazine - link to famous pheaker magazine web pages
    • A Zillion Different Ways To Make Your Very Own Red Box
    • FoNe BoXeZ - beige, black and other pheaker's boxes
    • G-Files - hacking, boxing and geek humour
    • Pheaking Sites Links - links from Yahoo
    • Phrack - information about everything you shouldn't know about telephone
    • Some Box Plans - plans for many telephone hacking boxes
    • The Hacker's Handbook - very early version of the book that was later banned in Great Britain in 1985
    • The Official Phreaker's Manual