| Radio
amateurs use Various modes of transmission to communicate.
Voice transmissions are most common, with some such as frequency
modulation (FM) offering high quality audio, and others
such as single sideband (SSB) offering more reliable communications
when signals are marginal and bandwidth is restricted.
Radiotelegraphy using Morse
code remains popular, particularly on the shortwave bands
and for experimental work, with its inherent signal-to-noise
ratio advantages. Morse, using internationally agreed code
groups, also facilitates communications between amateurs
who speak different languages. It is also popular with home
constructors as CW-only transmitters are simpler to construct.
Modern personal computers
have led to a boom in digital modes such as radioteletype,
which previously required cumbersome mechanical equipment.
Hams led the development of packet radio, which has since
been augmented by more specialized modes such as PSK31 to
facilitate real-time, low-power communications on the shortwave
bands. Other modes, such as WSJT, are used for weak signal
modes including meteor scatter and moonbounce communications.
Similarly, fast scan amateur
television, once considered rather esoteric, has exploded
in popularity thanks to cheap camcorders and video cards
in home computers. Because of the wide bandwidth and stable
signals required, fast scan amateur television is normally
limited to 100 km (about 60 miles) range.
However, with HAM TV repeaters
linked together the video may travel across several states.
Amateur radio station with vintage vacuum tube gear featuring
separate transmitter, receiver and power supply.
On VHF and higher frequencies,
automated relay stations, or repeaters, are used to increase
range. Repeaters are usually located on the top of a mountain
or tall building. A repeater allows the radio amateur to
communicate over hundreds of square miles using a low power
hand-held transceiver. Repeaters can also be linked together,
by use of other amateur radio bands, wireline, or the Internet.
Repeater stations are either owned, maintained and operated
by Clubs or individuals.
While many hams just enjoy
talking to friends, others pursue specialized interests
such as providing emergency communications for community
emergency response teams; designing new antennas; communicating
via amateur satellites; severe weather spotting; DX communication
to far away countries; using the Internet Radio Linking
Project (IRLP) to connect radio repeaters via the Internet;
tracking vehicles using the Automatic Position Reporting
System (APRS), which integrates with the GPS; engaging in
the sports of Contesting, Amateur Radio Direction Finding
and High Speed Telegraphy; or trying low-power operation.
Some enthusiasts collect vintage
amateur radios, such as those using vacuum tube technology.
Some hams also assist in the restoration and operation of
antique radio equipment at museums and museum ships.
Many hams enjoy meeting each
other in person as well through local clubs or at Hamfests.
These annual events are popular, with the largest being
held in Dayton Ohio, where more than 20,000 hams gather
each May. |