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Amateurs are permitted to use digital emissions (modes and protocols) at a wide variety of symbol rates (baud) from HF through microwave frequencies.

• Amateur digital modes - ARRL resources
• Amateurs are also developing high-speed wireless networks, both within the amateur segments of the 2.4 GHz band using WiFi and on other bands using mesh networking techniques.
• Amateur high-speed digital communications - ARRL resources
• Based on these digital modes, amateurs have also developed complete end-to-end communications systems.  For example, the Winlink email system has grown from casual use for sailors to a worldwide, hardened network that provides critical emergency and disaster relief communications.  The Automatic Packet Reporting System (APRS) was adapted to create the foundation for the commercial Lojack stolen vehicle recovery system - hams use it for position, weather, remote sensing, and text messaging.
• Amateur communications systems - ARRL resources
• Winlink 2000
• APRS
• TAPR - this organization supports and helps administer amateur experimental development of digital communications concepts.  TAPR also sponsors the ham radio Digital Communication Conference every year.

Understanding, modeling, and experimenting with antenna design is one of Amateur Radio's strongest suits.  Amateur bands span wavelengths from 160 meters (longer wavelength bands are coming but are not yet approved for amateur use by the FCC) through millimeter-wave.

• Antennas - ARRL resources
• RF Propagation - ARRL resources
• The ARRL Antenna Book is the standard reference book used by hams for antenna, transmission lines, and propagation information.  It comes with several software utilities on CD-ROM, including numerous antenna design models, a version of the EZNEC antenna modeling program, and the Yagi antenna design software YW (Yagis for Windows).
• At and above VHF, amateurs use the so-called "weak signal" modes: Morse, SSB, and advanced digital modes such as the WSJT software developed by Nobel laureate Joe Taylor, K1JT, for amateur meteor scatter and Earth-Moon-Earth communications (a.k.a. - "moonbounce").
• VHF-UHF Modes and Propagation - ARRL resources
• The RSGB (Radio Society of Great Britain) is also very active at VHF+ (VHF and higher frequency bands) as is the continental DUBUS group.
• UK Microwavers
• DUBUS

The ARRL provides numerous articles and tutorials on the use of transmission lines, measurements on transmission lines, and the use of the Smith chart as a tool for understanding and designing transmission line systems.
 

• Transmission Lines - ARRL resources
• Smith chart - ARRL resources
• The AT&T Archive features this excellent video presentation, "Similarities in Wave Behavior" by Dr John Shive, explaining basic wave phenomena by using his Shive Wave Generator.  The video illustrates basic concepts including speed of propagation, reflection, development of standing waves.  He also derives standing wave ratio and other metrics in a visual, easy-to-understand style.
• The ARRL Antenna Book is the standard reference book used by hams for antenna, transmission lines, and propagation information.  It comes with several software utilities on CD-ROM, including the handy transmission line calculator TLW (Transmission Lines for Windows).

The primary amateur satellite group is the Radio Amateur Satellite Corporation (AMSAT). AMSAT coordinates all amateur satellite communications links and maintains a record of satellite status, Keplerian orbital elements, and other information about the satellite.

University and other teams have been constructing and deploying small experimental satellites called CubeSats after their shape.  CubeSat, AMSAT, and the ARRL work together to manage CubeSat communication links.  There is Amateur Radio equipment you can contact, such as a digipeater, on the International Space Station, as well, with regular contacts between the astronauts and primary-secondary students around the world.

• CubeSat
• NASA CubeSat Initiative
• ARRL Satellite Handbook
• Amateur Radio on the ISS (ARISS)
• Searching the ARRL website for "cubesat" will also return numerous links to articles about Cubesats and Amateur Radio.  A CubeSat simulator is discussed on the Education and Technology Program's web page about Kits and Projects.
• High-altitude ballooning has become quite popular with student teams from high-schools and colleges as well as private groups.  Amateur Radio is often used as the communications link for position information, telemetry data from remote sensing platforms, and video/images.
• Amateur Radio High Altitude Ballooning (ARHAB)
• Edge of Space Sciences
• WB8ELK Balloons
• UK High Altitude Society
• Remote sensing platforms are also being developed that use Amateur Radio communications links to return data from land- and water-based experiments.  The article "ARRL Education and Technology Program Space/Sea Buoy" illustrates how amateurs are performing remote sensing experiments.
• The ARRL's Education and Technology Program has collected a number of kits, papers, and projects that support scientific experimentation and technology such as space-based communication, radio astronomy, seismometers, location trackers, "fox" (hidden transmitter) hunting, and more.  See the Kits and Projects page for more information.

The ARRL Handbook is the primary electronics reference used by amateurs.  It covers topics from basic electrical fundamentals through transceiver architecture and circuit design.

The book Experimental Methods in RF Design by Hayward, Campbell, and Larkin explores many advanced design topics at HF and VHF frequencies:

Hands-On Radio - a monthly column by Ward Silver NØAX - presents a two-page experiment or explanation of a technical topic for amateurs.  Two volumes of the experiments are available with 60 experiments in each: Volume 1 and Volume 2, as well as a parts kit.

Other resources include:

• RF and AF Filters - ARRL resources
• Reference circuits - typical amateur communication link parameters and metrics
• International Microwave Handbook - Radio Society of Great Britain (RSGB) technical handbook

Construction of circuits operating at RF requires special know-how and technique.  Here are a few resources to help you learn how to build electronics properly.

• Circuit construction - ARRL resources
• RF and electrical safety - ARRL resources
• ARRL Handbook - extensive material on home-built projects, use of test equipment, construction techniques, and both electrical and RF exposure safety from the perspective of amateur radio.

• ARRL Handbook
• ARRL Antenna Book
• Experimental Methods in RF Design by Hayward, Campbell, and Larkin
• Radio Society of Great Britain (RSGB) - International Microwave Handbook
• Online QST Archives (digital and print)
• ARRL Lab
• ARRL Product Reviews

Electronic Products magazine's

- lots of handy stuff for engineering and science students