Some of the most powerful capabilities of Amateur Radio are techniques that combine appropriate modulation (analog or digital) with protocols defined by computers or other special control logic to create a system.  Some examples:

• ALE (Automatic Link Establishment) is based on government standards for automatically connecting HF radios.  The protocol searches through available frequency bands and creates a channel that is appropriate for current band conditions.
• APRS (Automatic Packet Reporting System) is a system that automatically transmits a GPS position or other desired data using packet relay technology to interested monitoring stations.  APRS can be extended with Internet links to provide real-time information on a local, regional, or global basis.  Click this link for further details on APRS.
• Repeaters are automated receiver-transmitter systems that rebroadcast your signal enabling wide area coverage for even small handheld transceivers.  Sited at favorable hilltop locations, repeaters are most often used for FM voice service in the VHF and UHF bands.  Amateur Radio satellites operate special repeaters allowing contacts for thousands of miles.
• Internet Linked Systems are local stations or repeaters that are connected through Internet "tunnels" to extend your local VHF/UHF radio communications to sites around the world. Examples are Echolink, IRLP (Internet Radio Linking Project), WIRES-II, and D-STAR.
• Other Internet Based Systems.  Some amateurs operate remote base stations using special Internet links.  Email systems have been developed for emergency or maritime use, such as WinLink and PSKmail.

Repeaters (Regulatory)

• FCC Regulations
  Section 97.113 Prohibited transmissions
  Section 97.201 Auxiliary station
  Section 97.205 Repeater station
  Section 97.213 Telecommand of an amateur station

• Amateur Frequency Coordinators
• ARRL Bandplans

ALE

• A Federal Standard for HF Radio Automatic Link Establishment
  QEX January 1990, p. 3
• Growing Family of Federal Standards for HF Radio Automatic Link Establishment (ALE)
  Part I, QEX July 1993, pp. 3-8
  Part II, QEX August 1993, pp. 9-14
  Part III, QEX September 1993, pp. 14-19
  Part IV, QEX October 1993, pp. 13-18
  Part V, QEX November 1993, pp. 9-12
  Part VI, QEX December 1993, pp. 7-12
• ALE--The Coming of Automatic Link Establishment
  QST February 1995, p. 68 (Technical Correspondence)

Repeaters

• Once Upon a California Hilltop
  QST March 2004
  The story of repeater pioneer Art Gentry, W6MEP..
• Repeaters -- what are they and how to use them
• Glossary of Repeater Terms
• Anatomy of a Repeater
  QST May 1995, pp. 69-71
  FM hamming wouldn't be the same without these clever devices.
• How Are You Controlling Your Repeater?
  QST December 1999, pp. 81-82
• Crossband-Repeater Operation
  QST March 1993, pp. 43-46
  Dual-band VHF/UHF rigs offer flexible operating capabilities.
• Selective Calling
  A collection of articles from QST on using CTCSS and DTMF for selective calling.
• VHF/UHF and Repeaters: The Basics
  QST April 1998, p. 93
  Some repeater rules and regulations
• A Repeater Controller Accessory: The RCA
  QST February 2000, pp. 37-45
  Although designed initially for use with repeaters, this flexible controller can be adapted to many other applications. Let your imagination be your guide!
  Feedback
  QST May 2000, p. 45
• Build a $60 Talking Repeater Controller
  QST February 1997, pp. 37-40
  This inexpensive programmable controller features stored voice, simplex or duplex repeater control and low power consumption.
• Decoding the Secrets of CTCSS
  QST December 1996, pp. 55-56
  While most rigs can send these low-frequency audio tones, decoding them is a handy trick, too!
• A Microprocessor-Controlled Repeater Voting System: The RVS-8
  QST April 1996, pp. 38-43
  You can add this flexible voting system to virtually any repeater!
  Also see: RVS-8 Repeater Voter Audio-Amplifier IC Choice
  QST September 1996, p. 77, Technical Correspondence
• A Homebrew 2-meter Repeater
  QEX February 1996, pp. 12-18
  This design from the West Virginia Institute of Technology Amateur Radio Club uses off-the-shelf radios -- without modification.
• Beep... What Did That Repeater Say?
  QST September 1995, p. 75
  A single tone is often the only thing standing between us and chaos.
• Beeper Madness
  QST May 1994, pp.86-87 (Hints and Kinks)
  Here are two circuits for adding end-of-transmission beep to repeaters.
• The RingMaster Ring Detector
  QST April 1994, pp. 40-42
  In some areas, Caller ID can mean reduced security for repeaters controlled by phone lines. This circuit keeps hackers out.
• A Homemade Duplexer for 2-Meter Repeaters
  QST July 1972, pp. 22-26, 47
  Build a six-cavity duplexer for use with a 2-meter repeater.

ALE

• HFLINK
  HFLINK is the main coordinating resource for the use of Automatic Link Establishment in the International Amateur Radio Service. You have permission to use, and we encourage you to use the ALE channel listing.
• Automatic Link Establishment (ALE) Application Handbook
• Automatic Link Establishment (ALE)
  General Overview from Harris
• Simulation Results for Third-Generation HF Automatic Link
• PC-ALE Project
  A Windows program

Repeaters

• United Kingdom -- RSGB Repeater Management Committee
  (link at bottom of personal page)
• Operating Permit Information by Country
  Links to repeater information for many countries.

• Amateur Frequency Coordinators
  Contacting a Frequency Coordinator is a prerequisite to putting a repeater on the air.
• Internet Ham Radio (Echolink)
• Amateur Repeater Builders Home Page