Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
Radioteletype (RTTY) is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations connected by radio rather than a wired link. Radioteletype evolved from earlier landline teleprinter operations that began in the mid-1800s. The US Navy Department successfully tested printing telegraphy between an airplane and ground radio station in 1922. Later that year, the Radio Corporation of America successfully tested printing telegraphy via their Chatham, Massachusetts, radio station to the R.M.S. Majestic. Commercial RTTY systems were in active service between San Francisco and Honolulu as early as April 1932 and between San Francisco and New York City by 1934. The US military used radioteletype in the 1930s and expanded this usage during World War II. From the 1980s, teleprinters were replaced by personal computers (PCs) running software to emulate teleprinters.
In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Amplitude modulation produces an output signal the bandwidth of which is twice the maximum frequency of the original baseband signal. Single-sideband modulation avoids this bandwidth increase, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver.
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary FSK, in which the carrier is shifted between two discrete frequencies to transmit binary information.
In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The sidebands carry the information transmitted by the radio signal. The sidebands comprise all the spectral components of the modulated signal except the carrier. The signal components above the carrier frequency constitute the upper sideband (USB), and those below the carrier frequency constitute the lower sideband (LSB). All forms of modulation produce sidebands.
Slow-scan television (SSTV) is a picture transmission method, used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.
Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave as the wavelengths range from one to ten myriameters. Due to its limited bandwidth, audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines.
PSK31 or "Phase Shift Keying, 31 Baud", also BPSK31 and QPSK31, is a popular computer-sound card-generated radioteletype mode, used primarily by amateur radio operators to conduct real-time keyboard-to-keyboard chat, most often using frequencies in the high frequency amateur radio bands (near-shortwave). PSK31 is distinguished from other digital modes in that it is specifically tuned to have a data rate close to typing speed, and has an extremely narrow bandwidth, allowing many conversations in the same bandwidth as a single voice channel. This narrow bandwidth makes better use of the RF energy in a very narrow space thus allowing relatively low-power equipment to communicate globally using the same skywave propagation used by shortwave radio stations.
The Automatic Picture Transmission (APT) system is an analog image transmission system developed for use on weather satellites. It was introduced in the 1960s and over four decades has provided image data to relatively low-cost user stations at locations in most countries of the world. A user station anywhere in the world can receive local data at least twice a day from each satellite as it passes nearly overhead.
NAVTEX, sometimes styled Navtex or NavTex, is an international automated medium frequency direct-printing service for delivery of navigational and meteorological warnings and forecasts, as well as urgent maritime safety information (MSI) to ships.
Olivia MFSK is an amateur radioteletype protocol, using multiple frequency-shift keying (MFSK) and designed to work in difficult conditions on shortwave bands. The signal can be accurately received even if the surrounding noise is 10 dB stronger. It is commonly used by amateur radio operators to reliably transmit ASCII characters over noisy channels using the high frequency (3–30 MHz) spectrum. The effective data rate of the Olivia MFSK protocol is 150 characters/minute.
In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in baud (Bd) or symbols per second. In the case of a line code, the symbol rate is the pulse rate in pulses per second. Each symbol can represent or convey one or several bits of data. The symbol rate is related to the gross bit rate, expressed in bits per second.
AMTOR is a type of telecommunications system that consists of two or more electromechanical teleprinters in different locations that send and receive messages to one another. AMTOR is a specialized form of RTTY protocol. The term is an acronym for Amateur Teleprinting Over Radio and is derived from ITU-R recommendation 476-1 and is known commercially as SITOR developed primarily for maritime use in the 1970s. AMTOR was developed in 1978 by Peter Martinez, G3PLX, with the first contact taking place in September 1978 with G3YYD on the 2m Amateur band. It was developed on homemade Motorola 6800-based microcomputers in assembler code. It was used extensively by amateur radio operators in the 1980s and 1990s but has now fallen out of use as improved PC-based data modes are now used and teleprinters became out of fashion.
Q15X25 is a communications protocol for sending data over a radio link. It was designed by amateur radio operator Pawel Jalocha, SP9VRC, to be an open communications standard. Like all amateur radio communications modes, this protocol uses open transmissions which can be received and decoded by anyone with similar equipment. Q15X25 is a form of packet radio. It can be used to interconnect local VHF AX.25 packet networks over transcontinental distances. Anyone can design or adapt the open-source software to develop their own Q15X25 system.
WSJT-X is a computer program used for weak-signal radio communication between amateur radio operators. The program was initially written by Joe Taylor, K1JT, but is now open source and is developed by a small team. The digital signal processing techniques in WSJT-X make it substantially easier for amateur radio operators to employ esoteric propagation modes, such as high-speed meteor scatter and moonbounce. Additionally WSJT is able to send signal reports to spotting networks such as PSK Reporter.
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates oscillating electrical energy, often characterized as a wave. They can be received by other antennas connected to a radio receiver, this is the fundamental principle of radio communication. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.
Underwater acoustic communication is a technique of sending and receiving messages in water. There are several ways of employing such communication but the most common is by using hydrophones. Underwater communication is difficult due to factors such as multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation, especially over long ranges. Compared to terrestrial communication, underwater communication has low data rates because it uses acoustic waves instead of electromagnetic waves.
FT8 is a frequency shift keying digital mode of radio communication used by amateur radio operators worldwide. Following release on June 29, 2017, by its creators Joe Taylor, K1JT, and Steve Franke, K9AN, along with the software package WSJT, FT8 was adopted rapidly, becoming the most popular digital mode recorded by automatic spotting networks such as PSK Reporter within 2 years.
Project Boresight was a United States program that built radio-location systems to find the position of Russian submarines that were using burst communications. It was created as a top-secret program.
