- 1 General
- 2 Antenna
- 3 Modulation
- 4 Amateur radio
- 5 Radio control
- 6 Satellite
- 7 Radiosonde
- 8 TV
- 9 Data
- 9.1 Signals
- 9.2 Radiofax
- 9.3 Radioteletype
- 9.4 Packet radio
- 10 Mobile phone
- 11 Software-defined radio
- 11.1 Hardware
- 11.2 Software
- 11.3 Other
- 11.4 Telephony
- 11.5 Web SDR
- 12 to sort
- 13 RFID
- https://en.wikipedia.org/wiki/Intentional_radiator - any device that is deliberately designed to produce radio waves.Radio transmitters of all kinds, including the garage door opener, cordless telephone, cellular phone, wireless video sender, wireless microphone, and many others fall into this category.
- https://en.wikipedia.org/wiki/Smith_chart - invented by Phillip H. Smith (1905–1987), is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits. The Smith chart can be used to simultaneously display multiple parameters including impedances, admittances, reflection coefficients, scattering parameters, noise figure circles, constant gain contours and regions for unconditional stability, including mechanical vibrations analysis. The Smith chart is most frequently used at or within the unity radius region. However, the remainder is still mathematically relevant, being used, for example, in oscillator design and stability analysis. While the use of paper Smith charts for solving the complex mathematics involved in matching problems has been largely replaced by software based methods, the Smith charts display is still the preferred method of displaying how RF parameters behave at one or more frequencies, an alternative to using tabular information. Thus most RF circuit analysis software includes a Smith chart option for the display of results and all but the simplest impedance measuring instruments can display measured results on a Smith chart display.
- YouTube: Smith chart basics, part 1
- https://en.wikipedia.org/wiki/Wireless_communication - or sometimes simply wireless, is the transfer of information or power between two or more points that are not connected by an electrical conductor. The most common wireless technologies use radio waves. With radio waves distances can be short, such as a few meters for Bluetooth or as far as millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable applications, including two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of applications of radio wireless technology include GPS units, garage door openers, wireless computer mice, keyboards and headsets, headphones, radio receivers, satellite television, broadcast television and cordless telephones.
Somewhat less common methods of achieving wireless communications include the use of other electromagnetic wireless technologies, such as light, magnetic, ...used from about 1890 for the first radio transmitting and receiving technology, as in wireless telegraphy, until the new word radio replaced it around 1920. The term was revived in the 1980s and 1990s mainly to distinguish digital devices that communicate without wires, such as the examples listed in the previous paragraph, from those that require wires or cables. This became its primary usage in the 2000s, due to the advent of technologies such as LTE, LTE-Advanced, Wi-Fi and Bluetooth.
Wireless operations permit services, such as long-range communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and receivers, remote controls, etc.) which use some form of energy (e.g. radio waves, acoustic energy,) to transfer information without the use of wires. Information is transferred in this manner over both short and long distances.
- https://en.wikipedia.org/wiki/Wireless_telegraphy - the transmission of telegraphy signals from one point to another by means of an electromagnetic, electrostatic or magnetic field, or by electrical current through the earth or water. The term is used synonymously for radio communication systems, also called radiotelegraphy, which transmit telegraph signals by radio waves. When the term originated in the late 19th century it also applied to other types of experimental wireless telegraph communication technologies, such as conduction and induction telegraphy. Radio telegraphy often used manually-sent Morse code; radioteletype (RTTY) always uses mechanically generated and recorded characters.
- Part15 - License Free, legal, low-power radio broadcasting
- https://en.wikipedia.org/wiki/Frequency_agility - the ability of a radar system to quickly shift its operating frequency to account for atmospheric effects, jamming, mutual interference with friendly sources, or to make it more difficult to locate the radar broadcaster through radio direction finding. The term can also be applied to other fields, including lasers or traditional radio transceivers using frequency-division multiplexing, but it remains most closely associated with the radar field and these other roles generally use the more generic term "frequency hopping".
- https://en.wikipedia.org/wiki/Transmitter - an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves.
- https://en.wikipedia.org/wiki/Link_budget - accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc.) to the receiver in a telecommunication system. It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feedline and miscellaneous losses. Randomly varying channel gains such as fading are taken into account by adding some margin depending on the anticipated severity of its effects. The amount of margin required can be reduced by the use of mitigating techniques such as antenna diversity or frequency hopping.
A simple link budget equation looks like this: Received Power (dB) = Transmitted Power (dB) + Gains (dB) − Losses (dB). Note that decibels are logarithmic measurements, so adding decibels is equivalent to multiplying the actual numeric ratios.
- https://en.wikipedia.org/wiki/QRP_operation - refers to transmitting at reduced power while attempting to maximize one's effective range. The term QRP derives from the standard Q code used in radio communications, where "QRP" and "QRP?" are used to request, "Reduce power", and ask "Should I reduce power?" respectively. The opposite of QRP is QRO, or high-power operation.
- https://en.wikipedia.org/wiki/RF_power_amplifier - a type of electronic amplifier that converts a low-power radio-frequency signal into a higher power signal. Typically, RF power amplifiers drive the antenna of a transmitter. Design goals often include gain, power output, bandwidth, power efficiency, linearity (low signal compression at rated output), input and output impedance matching, and heat dissipation.
- https://en.wikipedia.org/wiki/Radio_receiver - an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. The antenna intercepts radio waves (electromagnetic waves) and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The receiver uses electronic filters to separate the desired radio frequency signal from all the other signals picked up by the antenna, an electronic amplifier to increase the power of the signal for further processing, and finally recovers the desired information through demodulation.
- https://en.wikipedia.org/wiki/Radio_receiver_design - includes the electronic design of different components of a radio receiver which processes the radio frequency signal from an antenna in order to produce usable information such as audio. The complexity of a modern receiver and the possible range of circuitry and methods employed are more generally covered in electronics and communications engineering. The term radio receiver is understood in this article to mean any device which is intended to receive a radio signal in order to generate useful information from the signal, most notably a recreation of the so-called baseband signal (such as audio) which modulated the radio signal at the time of transmission in a communications or broadcast system.
- https://en.wikipedia.org/wiki/Regenerative_circuit - an amplifier circuit that employs positive feedback (also known as regeneration or reaction). Some of the output of the amplifying device is applied back to its input so as to add to the input signal, increasing the amplification. One example is the Schmitt trigger (which is also known as a regenerative comparator), but the most common use of the term is in RF amplifiers, and especially regenerative receivers, to greatly increase the gain of a single amplifier stage.
- https://en.wikipedia.org/wiki/Tuned_radio_frequency_receiver - or TRF receiver, is a type of radio receiver that is composed of one or more tuned radio frequency (RF) amplifier stages followed by a detector (demodulator) circuit to extract the audio signal and usually an audio frequency amplifier. This type of receiver was popular in the 1920s. Early examples could be tedious to operate because when tuning in a station each stage had to be individually adjusted to the station's frequency, but later models had ganged tuning, the tuning mechanisms of all stages being linked together, and operated by just one control knob. By the mid 1930s, it was replaced by the superheterodyne receiver patented by Edwin Armstrong.
- https://en.wikipedia.org/wiki/Reflex_receiver - occasionally called a reflectional receiver, is a radio receiver design in which the same amplifier is used to amplify the high-frequency radio signal (RF) and low-frequency audio (sound) signal (AF). It was first invented in 1914 by German scientists Wilhelm Schloemilch and Otto von Bronk, and rediscovered and extended to multiple tubes in 1917 by Marius Latour and William H. Priess. The radio signal from the antenna and tuned circuit passes through an amplifier, is demodulated in a detector which extracts the audio signal from the radio carrier, and the resulting audio signal passes again through the same amplifier for audio amplification before being applied to the earphone or loudspeaker. The reason for using the amplifier for "double duty" was to reduce the number of active devices, vacuum tubes or transistors, required in the circuit, to reduce the cost. The economical reflex circuit was used in inexpensive vacuum tube radios in the 1920s, and was revived again in simple portable tube radios in the 1930s.
- https://en.wikipedia.org/wiki/Superheterodyne_receiver - often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. It was invented by US engineer Edwin Armstrong in 1918 during World War I. Virtually all modern radio receivers use the superheterodyne principle.
- YouTube: Super Heterodyne basics, K7PP Page
- https://en.wikipedia.org/wiki/Frequency_mixer - a nonlinear electrical circuit that creates new frequencies from two signals applied to it. In its most common application, two signals are applied to a mixer, and it produces new signals at the sum and difference of the original frequencies. Other frequency components may also be produced in a practical frequency mixer.
- https://en.wikipedia.org/wiki/Heterodyne - a signal processing technique invented by Canadian inventor-engineer Reginald Fessenden that creates new frequencies by combining or mixing two frequencies. Heterodyning is used to shift one frequency range into another, new one, and is also involved in the processes of modulation and demodulation. The two frequencies are combined in a nonlinear signal-processing device such as a vacuum tube, transistor, or diode, usually called a mixer.
- https://en.wikipedia.org/wiki/Intermediate_frequency - a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a signal at the difference or beat frequency. Intermediate frequencies are used in superheterodyne radio receivers, in which an incoming signal is shifted to an IF for amplification before final detection is done.Conversion to an intermediate frequency is useful for several reasons. When several stages of filters are used, they can all be set to a fixed frequency, which makes them easier to build anreflectional receiverd to tune. Lower frequency transistors generally have higher gains so fewer stages are required. It's easier to make sharply selective filters at lower fixed frequencies.There may be several such stages of intermediate frequency in a superheterodyne receiver; two or three stages are called double (alternatively, dual) or triple conversion, respectively.
- https://en.wikipedia.org/wiki/Direct-conversion_receiver - also known as homodyne, synchrodyne, or zero-IF receiver, is a radio receiver design that demodulates the incoming radio signal using synchronous detection driven by a local oscillator whose frequency is identical to, or very close to the carrier frequency of the intended signal. This is in contrast to the standard superheterodyne receiver where this is accomplished only after an initial conversion to an intermediate frequency. The simplification of performing only a single frequency conversion reduces the basic circuit complexity but other issues arise, for instance, regarding dynamic range and image rejection. In its original form it was unsuited to receiving AM and FM signals without implementing an elaborate phase locked loop. Although these and other technical challenges made this technique rather impractical around the time of its invention (1930's), current technology, and software radio in particular, have revived its use in certain areas including some consumer products.
- https://en.wikipedia.org/wiki/Air_interface - or access mode, is the communication link between the two stations in mobile or wireless communication. The air interface involves both the physical and data link layers (layer 1 and 2) of the OSI model for a connection
- https://en.wikipedia.org/wiki/Duplex_(telecommunications) - a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX).
- https://en.wikipedia.org/wiki/Selective_calling - used to address a subset of all two-way radios on a single radio frequency channel. Where more than one user is on the same channel, (co-channel users,) selective calling can address a subset of all receivers or can direct a call to a single radio. Selective calling features fit into two major categories — individual calling and group calling. Individual calls generally have longer time-constants: it takes more air-time to call an individual radio unit than to call a large group of radios.Selective calling is akin to the use of a lock on a door. A radio with carrier squelch is unlocked and will let any signal in. Selective calling locks out all signals except ones with the correct "key", in this case a specific digital code. Selective calling systems can overlap; a radio may have (group call) and DTMF individual calling.
- https://en.wikipedia.org/wiki/Call_sign - also known as a call name' or call letters, historically as a call signal, or abbreviated as a call, is a unique designation for a transmitter station. In North America, they are used for all FCC-licensed transmitters. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or even cryptographically encoded to disguise a station's identity. The use of call signs as unique identifiers dates to the landline railroad telegraph system. Because there was only one telegraph line linking all railroad stations, there needed to be a way to address each one when sending a telegram. In order to save time, two-letter identifiers were adopted for this purpose. This pattern continued in radiotelegraph operation; radio companies initially assigned two-letter identifiers to coastal stations and stations aboard ships at sea. These were not globally unique, so a one-letter company identifier (for instance, 'M' and two letters as a Marconi station) was later added. By 1912, the need to quickly identify stations operated by multiple companies in multiple nations required an international standard; an ITU prefix would be used to identify a country, and the rest of the call sign an individual station in that country.
- https://en.wikipedia.org/wiki/Radio_spectrum - the part of the electromagnetic spectrum from 3 Hz to 3000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are extremely widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).
Different parts of the radio spectrum are appointed by the ITU for different radio transmission technologies and applications; some 40 radiocommunication services are defined in the ITU's Radio Regulations (RR). In some cases, parts of the radio spectrum are sold or licensed to operators of private radio transmission services (for example, cellular telephone operators or broadcast television stations). Ranges of allocated frequencies are often referred to by their provisioned use (for example, cellular spectrum or television spectrum).
- https://en.wikipedia.org/wiki/Extremely_low_frequency - electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. In atmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz. In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3 Hz) are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands.
ELF radio waves are generated by lightning and natural disturbances in Earth's magnetic field, so they are a subject of research by atmospheric scientists. Because of the difficulty of building antennas that can radiate such long waves, ELF frequencies have been used in only a very few human-made communication systems. ELF waves can penetrate seawater, which makes them useful in communication with submarines. The US, Russia, and India are the only nations known to have constructed ELF communication facilities. The U.S. facilities were used between 1985 and 2004 but are now decommissioned. ELF waves can also penetrate significant distances into earth or rock, and "through-the-earth" underground mine communication systems use frequencies of 300 to 3000 Hz. The frequency of alternating current flowing in electric power grids, 50 or 60 Hz, also falls within the ELF band, making power grids an unintentional source of ELF radiation.
- https://en.wikipedia.org/wiki/Super_low_frequency - frequency range between 30 hertz and 300 hertz. They have corresponding wavelengths of 10,000 to 1,000 kilometers. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz). Another conflicting designation which includes this frequency range is Extremely Low Frequency (ELF), which in some contexts refers to all frequencies up to 300 hertz.
- https://en.wikipedia.org/wiki/Ultra_low_frequency - frequency range of electromagnetic waves between 300 hertz and 3 kilohertz. In magnetosphere science and seismology, alternative definitions are usually given, including ranges from 1 mHz to 100 Hz, 1 mHz to 1 Hz, 10 mHz to 10 Hz. Frequencies above 3 Hz in atmosphere science are usually assigned to the ELF range.
- https://en.wikipedia.org/wiki/Very_low_frequency - radio frequencies (RF) in the range of 3 kHz to 30 kHz and corresponding wavelengths from 100 to 10 kilometres
- https://en.wikipedia.org/wiki/Low_frequency - LF is the ITU designation for radio frequencies (RF) in the range of 30 kHz–300 kHz. As its wavelengths range from ten kilometres to one kilometre, respectively, it is also known as the kilometre band or kilometre wave. LF radio waves exhibit low signal attenuation, making them suitable for long-distance communications. In Europe and areas of Northern Africa and Asia, part of the LF spectrum is used for AM broadcasting as the "longwave" band. In the western hemisphere, its main use is for aircraft beacon, navigation (LORAN), information, and weather systems. A number of time signal broadcasts are also broadcast in this band.
- https://en.wikipedia.org/wiki/Longwave - also written as long wave (in British and American parlance) or long-wave, and commonly abbreviated LW, refers to parts of the radio spectrum with relatively long wavelengths. The term is an historic one, dating from the early 20th century, when the radio spectrum was considered to consist of long (LW), medium (MW) and short (SW) radio wavelengths. Most modern radio systems and devices use wavelengths which would then have been considered 'ultra-short'.
In contemporary usage, the term longwave is not defined precisely, and its meaning varies across the world. Most commonly, it refers to radio wavelengths longer than 1000 metres; frequencies less than 300 kilohertz (kHz), including the International Telecommunications Union's (ITU's) low frequency (LF) (30–300 kHz) and very low frequency (VLF) (3–30 kHz) bands. Sometimes, part of the medium frequency (MF) band (300–3000 kHz) is included.
- https://en.wikipedia.org/wiki/Medium_wave - the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. For Europe the MW band ranges from 526.5 kHz to 1606.5 kHz, using channels spaced every 9 kHz, and in North America an extended MW broadcast band goes from 535 kHz to 1705 kHz, using 10 kHz spaced channels.
- https://en.wikipedia.org/wiki/Shortwave_radio - radio transmission using shortwave frequencies, generally 1.6–30 MHz (187.4–10.0 m), just above the medium wave AM broadcast band.
Radio waves in this band can be reflected or refracted from a layer of electrically charged atoms in the atmosphere called the ionosphere. Therefore short waves directed at an angle into the sky can be reflected back to Earth at great distances, beyond the horizon. This is called skywave or skip propagation. Thus shortwave radio can be used for very long distance communication, in contrast to radio waves of higher frequency which travel in straight lines (line-of-sight propagation) and are limited by the visual horizon, about 40 miles. Shortwave radio is used for broadcasting of voice and music to shortwave listeners over very large areas; sometimes entire continents or beyond. It is also used for military over-the-horizon radar, diplomatic communication, and two-way international communication by amateur radio enthusiasts for hobby, educational and emergency purposes.
- https://en.wikipedia.org/wiki/160-meter_band - top band (AM), refers to the band of radio frequencies between 1800 and 2000 kHz
- https://en.wikipedia.org/wiki/High_frequency - between 3 and 30 MHz. It is also known as the decameter band or decameter wave
- https://en.wikipedia.org/wiki/Very_high_frequency - VHF, from 30 MHz to 300 MHz
- https://en.wikipedia.org/wiki/Ultra_high_frequency - UHF, between 300 MHz and 3 GHz, also known as the decimetre band as the wavelengths range from one meter to one decimetre
- https://en.wikipedia.org/wiki/Microwave - with wavelengths ranging from one meter to one millimeter; with frequencies between 300 MHz (100 cm) and 300 GHz (0.1 cm). This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often restricting the range between 1 and 100 GHz (300 and 3 mm).
The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range. It indicates that microwaves are "small", compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study.
- https://en.wikipedia.org/wiki/Super_high_frequency - SHF, between 3 GHz and 30 GHz. This band of frequencies is also known as the centimetre band or centimetre wave
- https://en.wikipedia.org/wiki/Extremely_high_frequency - EHF, from 30 to 300 gigahertz. It lies between the super high frequency band, and the far infrared band which is also referred to as the terahertz gap. Radio waves in this band have wavelengths from ten to one millimetre, giving it the name millimetre band or millimetre wave, sometimes abbreviated MMW or mmW. Millimetre-length electromagnetic waves were first investigated in the 1890s by Indian scientist Jagadish Chandra Bose.
- https://en.wikipedia.org/wiki/Terahertz_radiation - also known as submillimeter radiation, terahertz waves, tremendously high frequency, T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terahertz (THz; 1 THz = 1012 Hz). Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.1 mm (or 100 μm). Because terahertz radiation begins at a wavelength of one millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy.
Terahertz radiation occupies a middle ground between microwaves and infrared light waves known as the terahertz gap, where technology for its generation and manipulation is in its infancy. It represents the region in the electromagnetic spectrum where the frequency of electromagnetic radiation becomes too high to be measured digitally via electronic counters, so must be measured by proxy using the properties of wavelength and energy. Similarly, the generation and modulation of coherent electromagnetic signals in this frequency range ceases to be possible by the conventional electronic devices used to generate radio waves and microwaves, requiring the development of new devices and techniques. Photon energy in THz regime is less than band-gap of nonmetallic materials and thus THz beam can traverse through such materials. The transmitted THz beam is used for material characterization, layer inspection and developing transmission images.
- https://en.wikipedia.org/wiki/Terahertz_gap - an engineering term for a band of frequencies in the terahertz region of the electromagnetic spectrum between radio waves and infrared light for which practical technologies for generating and detecting the radiation do not exist. It is defined as 0.1 to 10 THz (wavelengths of 3 mm to 30 µm). Currently, at frequencies within this range, useful power generation and receiver technologies are inefficient and impractical.
- https://en.wikipedia.org/wiki/Far_infrared - often defined as any radiation with a wavelength of 15 micrometers (µm) to 1 mm (corresponding to a range of about 20 THz to 300 GHz), which places far infrared radiation within the CIE IR-B and IR-C bands. Different sources use different boundaries for the far infrared spectrum; for example, astronomers sometimes define far infrared as wavelengths between 25 µm and 350 µm. Visible light includes radiation with wavelengths between 400 nm and 700 nm, meaning that far infrared photons have less energy than visible light photons.
- http://www.sigidwiki.com/wiki/Signal_Identification_Guide - wiki intended to help identify radio signals through example sounds and waterfall images. Most signals are received and recorded using a software defined radio such as the RTL-SDR, Airspy, SDRPlay, HackRF, BladeRF, Funcube Dongle, USRP or others. 
- The principles underlying radio communication : United States. National Bureau of Standards : Free Download, Borrow, and Streaming : Internet Archive
- A.T.V - probably the most extensive aerials site on the Internet and in 2017 we had 370,000 visitors with 810,000 page hits. In fact even “the trade” use this site. Actually, even we use it if we want to check up on anything to do with aerials !
- https://en.wikipedia.org/wiki/Antenna_feed - refers to several slightly different parts of an antenna system: The antenna feed is the wire or cabling (transmission line) that connects between the antenna and the radio, specifically called the feed line; The antenna feed is the location on the antenna where the feedline from the receiver or transmitter connects or attaches; The antenna feed is the matching system at the attachment point that converts the feedline impedance to the antenna’s intrinsic impedance, and makes any balanced-to-unbalanced conversion (if necessary).
- https://en.wikipedia.org/wiki/Feed_horn - In parabolic antennas such as satellite dishes, a feed horn (or feedhorn) is a small horn antenna used to convey radio waves between the transmitter and/or receiver and the parabolic reflector. In transmitting antennas, it is connected to the transmitter and converts the radio frequency alternating current from the transmitter to radio waves and feeds them to the rest of the antenna, which focuses them into a beam. In receiving antennas, incoming radio waves are gathered and focused by the antenna's reflector on the feed horn, which converts them to a tiny radio frequency voltage which is amplified by the receiver. Feed horns are used mainly at microwave (SHF) and higher frequencies.
- https://en.wikipedia.org/wiki/Hirose_U.FL - a miniature RF connector for high-frequency signals up to 6 GHz manufactured by Hirose Electric Group and others.U.FL connectors are commonly used in applications where space is of critical concern, most often Mini PCI cards for laptop computers. U.FL connectors are commonly used inside laptops and embedded systems to connect the Wi-Fi antenna to a Mini PCI card. Another common use is connecting GPS antennas.
- Amateur Radio Stack Exchange: antenna - What makes a 5/8 wavelength vertical desirable?
- https://en.wikipedia.org/wiki/Horn_antenna - or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are used as feed antennas (called feed horns) for larger antenna structures such as parabolic antennas, as standard calibration antennas to measure the gain of other antennas, and as directive antennas for such devices as radar guns, automatic door openers, and microwave radiometers. Their advantages are moderate directivity, low standing wave ratio (SWR), broad bandwidth, and simple construction and adjustment.
- https://en.wikipedia.org/wiki/Yagi–Uda_antenna - ommonly known as a Yagi antenna, is a directional antenna consisting of multiple parallel elements in a line, usually half-wave dipoles made of metal rods. Yagi–Uda antennas consist of a single driven element connected to the transmitter or receiver with a transmission line, and additional "parasitic elements" which are not connected to the transmitter or receiver: a so-called reflector and one or more directors. It was invented in 1926 by Shintaro Uda of Tohoku Imperial University, Japan, and (with a lesser role played by his colleague) Hidetsugu Yagi. The reflector element is slightly longer than the driven dipole, whereas the directors are a little shorter. The parasitic elements absorb and reradiate the radio waves from the driven element with a different phase, modifying the dipole's radiation pattern. The waves from the multiple elements superpose and interfere to enhance radiation in a single direction, achieving a very substantial increase in the antenna's gain compared to a simple dipole.Also called a "beam antenna",or "parasitic array", the Yagi is very widely used as a high-gain antenna on the HF, VHF and UHF bands. It has moderate to high gain which depends on the number of elements used, typically limited to about 20 dBi, linear polarization, unidirectional (end-fire) beam pattern with high front-to-back ratio of up to 20 db. and is lightweight, inexpensive and simple to construct. The bandwidth of a Yagi antenna, the frequency range over which it has high gain, is narrow, a few percent of the center frequency, and decreases with increasing gain, so it is often used in fixed-frequency applications. The largest and best-known use is as rooftop terrestrial television antennas, but it is also used for point-to-point fixed communication links, in radar antennas, and for long distance shortwave communication by shortwave broadcasting stations and radio amateurs.
- Simple Wi-Fi Yagi - It's easy to make a small Yagi for a wireless router even if it lacks an antenna connector. The photo shows how I added two parasitic elements to the sleeve dipole of my Netgear WGR614. 
- https://en.wikipedia.org/wiki/Loop_antenna - a radio antenna consisting of a loop or coil of wire, tubing, or other electrical conductor usually fed by a balanced source or feeding a balanced load. Within this physical description there are two distinct antenna types. The large self-resonant loop antenna has a circumference close to one wavelength of the operating frequency and so is resonant at that frequency. This category also includes smaller loops 5% to 30% of a wavelength in circumference, which use a capacitor to make them resonant. These antennas are used for both transmission and reception. In contrast, small loop antennas less than 1% of a wavelength in size are very inefficient radiators, and so are only used for reception. An example is the ferrite (loopstick) antenna used in most AM broadcast radios. Loop antennas have a dipole radiation pattern; they are most sensitive to radio waves in two broad lobes in opposite directions, 180° apart. Due to this directional pattern they are used for radio direction finding (RDF), to locate the position of a transmitter.
- https://en.wikipedia.org/wiki/Evolved_antenna - an antenna designed fully or substantially by an automatic computer design program that uses an evolutionary algorithm that mimics Darwinian evolution. This sophisticated procedure has been used in recent years to design a few antennas for mission-critical applications involving stringent, conflicting, or unusual design requirements, such as unusual radiation patterns, for which none of the many existing antenna types are adequate. 
- https://en.wikipedia.org/wiki/Leaky_feeder - a communications system used in underground mining and other tunnel environments. Manufacturers and cabling professionals use the term "radiating cable" as this implies that the cable is designed to radiate: something that coaxial cable is not generally supposed to do.
AM radio ranges from 535 to 1705 kilohertz, stations are possible every 10 kHz.
- System Bus Radio - Transmits AM radio on computers without radio transmitting hardware.
- http://www.erikyyy.de/tempest - CRT transmitter
FM radio ranges in a higher spectrum from 88 to 108 megahertz, stations are possible every 200 kHz.
- C. Crane FM2 Digital Full Spectrum FM Transmitter
- http://www.vastint.com/en-us/products/usb-rds-low-power-fm-transmitter-v-fmt212r - usb audio, minicoax
- Aareff: 100mW PLL FM Stereo Transmitter - proper
- https://github.com/UoC-Radio/JMPXRDS - FM MPX signal generator with RDS support on top of Jack Audio Connection Kit
- https://en.wikipedia.org/wiki/MPX_filter - a function found in cassette decks. Residual high-frequency components of the signal remaining after de-multiplexing can be problematic when recording to analog magnetic media. While the higher frequencies are unlikely to survive filtering in the recording deck, the 19 kHz tone is within the 20 to 20,000 Hz frequency range for many tape formats, including compact cassette, and typically provides an audible beat (difference) tone in conjunction with the tape head bias signal used when recording. The recording may also be saturated by the pilot tone. More importantly, the pilot tone interferes with the proper functioning of noise reduction systems such as Dolby B, C and S. Because the pilot tone is relatively loud in comparison to the overall loudness of the FM program (typically -20dB), the source signal is not correctly processed by the noise reduction system, leading to audible artefacts such as breathing and pumping. For this reason many decks with defeatable MPX filters have been designed in such a way that the MPX filter can only be enabled when also a noise reduction system is enabled.
- https://en.wikipedia.org/wiki/In-band_on-channel - a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency.
- https://en.wikipedia.org/wiki/Digital_audio_broadcasting - DAB standard was initiated as a European research project in the 1980s. The Norwegian Broadcasting Corporation (NRK) launched the first DAB channel in the world on 1 June 1995 (NRK Klassisk), and the BBC and Swedish Radio (SR) launched their first DAB digital radio broadcasts in September 1995. DAB receivers have been available in many countries since the end of the 1990s.
Audio quality varies depending on the bitrate used and audio material. Most stations use a bit rate of 128 kbit/s or less with the MP2 audio codec, which requires 160 kbit/s to achieve perceived FM quality. 128 kbit/s gives better dynamic range or signal-to-noise ratio than FM radio, but a more smeared stereo image, and an upper cut-off frequency of 14 kHz, corresponding to 15 kHz of FM radio. However, "CD quality" sound with MP2 is possible "with 256…192 kbps".
An upgraded version of the system was released in February 2007, which is called DAB+. DAB is not forward compatible with DAB+, which means that DAB-only receivers are not able to receive DAB+ broadcasts. However, broadcasters can mix DAB and DAB+ programs inside the same transmission and so make a progressive transition to DAB+. DAB+ is approximately twice as efficient as DAB, and more robust.
HD Radio / NRSC-5
- https://github.com/theori-io/nrsc5 - NRSC-5 receiver for rtl-sdr
- https://en.wikipedia.org/wiki/Digital_audio_radio_service - Satellite Digital Audio Radio Service, used by Sirius Satellite Radio and XM Satellite Radio. XM and Sirius both operate in the 2.3-GHz S band, from 2320 to 2345 MHz.
- https://en.wikipedia.org/wiki/Digital_Radio_Mondiale - DRM, a set of digital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting including AM broadcasting, particularly shortwave, and FM broadcasting. DRM is more spectrally efficient than AM and FM, allowing more stations, at higher quality, into a given amount of bandwidth, using various MPEG-4 audio coding formats.
- Dream - Open-Source Software Implementation of a DRM (Digital Radio Mondiale) Receiver under the GNU General Public License (GPL).
- https://en.wikipedia.org/wiki/CAM-D - Compatible Amplitude Modulation - Digital or CAM-D is a hybrid digital radio format for AM broadcasting, proposed by broadcast engineer Leonard R. Kahn.The system is an in-band on-channel technology that uses the sidebands of any AM radio station. Analog information is still used up to a bandpass of about 7.5kHz, with standard amplitude modulation. The missing treble information that AM normally lacks is then transmitted digitally beyond this. Audio mixing in the receiver then blends them back together.
Unlike other IBOC technologies like iBiquity's HD Radio, Kahn's apparently does not provide a direct path to all-digital transmissions, nor any multichannel capability. Its advantage, however, is that it takes up far less of the sidebands, thereby causing far less interference to adjacent channels, hence the "Compatible" in the name. Interference has affected HD Radio on AM, along with its (like CAM-D) proprietary nature.
Digital Radio Mondiale, commonly used in shortwave broadcasting, can use less, the same, or more bandwidth as AM, to provide high quality audio. Digital Radio Mondiale requires digital detection circuitry not present in conventional AM radios to decode programming.Special CAM-D receivers provide the benefit of better frequency response and a slow auxiliary data channel for display of station ID, programming titles, etc.
- https://en.wikipedia.org/wiki/Trunked_radio_system - two-way radio system that uses a control channel to automatically direct radio traffic. Two-way radio systems are either trunked or conventional, where conventional is manually directed by the radio user. Trunking is a more automated and complex radio system, but provides the benefits of less user intervention to operate the radio and greater spectral efficiency with large numbers of users. Instead of assigning, for example, a radio channel to one particular organization at a time, users are instead assigned to a logical grouping, a "talkgroup". When any user in that group wishes to converse with another user in the talkgroup, a vacant radio channel is found automatically by the system and the conversation takes place on that channel. Many unrelated conversations can occur on a channel, making use of the otherwise idle time between conversations. Each radio transceiver contains a microcomputer to control it. A control channel coordinates all the activity of the radios in the system. The control channel computer sends packets of data to enable one talkgroup to talk together, regardless of frequency.
- https://github.com/robotastic/trunk-recorder - Trunk Recorder is able to record the calls on trunked and conventional radio systems. It uses 1 or more Software Defined Radios (SDRs) to do this. The SDRs capture large swatches of RF and then use software to process what was received. GNURadio is used to do this processing because it provides lots of convenient RF blocks that can be pieced together to allow for complex RF processing. The libraries from the amazing OP25 project are used for a lot of the P25 functionality. Multiple radio systems can be recorded at the same time.
- https://en.wikipedia.org/wiki/Amateur_radio - also called ham radio, describes the use of radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communication. The term "amateur" is used to specify "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest;" (either direct monetary or other similar reward) and to differentiate it from commercial broadcasting, public safety (such as police and fire), or professional two-way radio services (such as maritime, aviation, taxis, etc.).
The amateur radio service (amateur service and amateur-satellite service) is established by the International Telecommunication Union (ITU) through the International Telecommunication Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with an identifying call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics and the host government's radio regulations. Radio amateurs use a variety of voice, text, image, and data communications modes and have access to frequency allocations throughout the RF spectrum to enable communication across a city, region, country, continent, the world, or even into space.
- Amateur-radio-wiki - This site aims to enable ham operators and curious alike to document, share and explore the fantastic world of amateur radio.
- ham-radio.com - site and it's hosted organizations offered as a free service to the Amateur Radio community.
- http://radio-hobby.org - Russian
- http://arstechnica.com/gadgets/2016/06/when-everything-else-fails-amateur-radio-will-still-be-there-and-thriving/ 
- Guerrilla Radio - How some inmates hack, rewire, and retool their radios to create walkie-talkies. 
- Fldigi - a modem program for most of the digital modes used by radio amateurs today: CW, PSK, MFSK, RTTY, Hell, DominoEX, Olivia, and Throb are all supported. It can help calibrate a sound card to a time signal and do frequency measurement tests.
- FreeDV: Open Source Amateur Digital Voice – Where Amateur Radio Is Driving The State of the Art - a Digital Voice mode for HF radio. You can run FreeDV using a free GUI application for Windows, Linux and OSX that allows any SSB radio to be used for low bit rate digital voice. Alternatively you can buy a SM1000 FreeDV adaptor that allows you to run FreeDV on any HF radio without a PC or sound card. If you are a hardware or software developer, you can integrate FreeDV into your project using the LGPL licensed FreeDV API. Speech is compressed down to 700-1600 bit/s then modulated onto a 1.25 kHz wide signal comprised of 16 QPSK carriers which is sent to the Mic input of a SSB radio. The signal is received by an SSB radio, then demodulated and decoded by FreeDV. FreeDV 700C is approaching SSB in it’s low SNR performance. At high SNRs FreeDV 1600 sounds like FM, with no annoying analog HF radio noise. FreeDV was built by an international team of Radio Amateurs working together on coding, design, user interface and testing. FreeDV is open source software, released under the GNU Public License version 2.1. The modems and Codec 2 speech codec used in FreeDV are also open source.
- http://linux.die.net/man/1/radio - in the xawtv package
- https://github.com/darksidelemm/hfssdv - Send Slow-Scan Digital Video (images) over HF via a KISS TNC!
- https://github.com/dh1tw/remoteAudio - a cross plattform audio streaming application, built for Amateur Radio purposes. The most typical use case for this software is the remote operation of an amateur radio station. remoteAudio is written in Go.
- HamWAN - a non-profit organization (501c3) developing best practices for high speed amateur radio data networks. HamWAN also runs the Puget Sound Data Ring, which is a real-world network implementation of the proposed designs.So far, HamWAN networks have been used for things like low-latency repeater linking, real-time video feeds from distant locations, serving APRS I-gates, providing redundant internet access to emergency operations centers, and more. Any licensed radio amateur in the service area can connect their shack directly to the network with just a small investment in equipment and no recurring cost. Since many traditional uses for Internet at home are not compatible with Part 97 rules, this won't replace your home Internet connection. However, it works and acts just like one.
- DV Access Point Dongle - connects to your PC or Intel based Mac via a USB port and provides a 2 meter Access Point for use with a D-STAR radio. Using an Internet connection, a user may connect to and communicate with D-STAR gateways and reflectors around the world. The DVAPTool application used with the DV Access Point Dongle may be installed and run on Microsoft Windows XP/Vista/7, Mac OS X Leopard/Snow Leopard, or many flavors of Linux.
- DV Dongle - connects to your PC or Apple Mac via a USB port and provides encoding and decoding of compressed audio using the DVSI AMBE2000 full duplex vocoder DSP chip. AMBE technology is used in all D-Star radios to provide efficient voice transmissions. It is also used in some HF digital protocols by vendors like AOR. The DVTool application used with the DV Dongle may be installed and run on Microsoft Windows XP/Vista/7/8/10, Mac OS X, or many flavors of Linux.
- DV MEGA - The goal of the DV-MEGA project is to develop a KIT for a dual-band D-Star transceiver.Because this can't be done overnight different modules will be available all based on theD-Star stream. The D-Star steam is common to a DV-node adapter, radio hotspot and transceiver.
- openSPOT2 – SharkRF - sucessor of the openSPOT
- pistar - a software image built initially for the Raspberry Pi (produced by the Raspberry Pi Foundation).The design concept is simple, provide the complex services and configuration for Digial Voice on Amateur radio in a way that makes it easily accessable to anyone just starting out, but make it configurable enough to be interesting for those of us who cant help but tinker.Pi-Star would not be here today, were it not for the software made by Jonathan Naylor (G4KLX), we started with his DStarRepeater and ircDDBGateway and now support the full G4KLX MMDVM suite, including the extra cross-mode gateways added on by Andy (CA6JAU), I cannot thank these guys for the vast amount of time and effort that they continue to put into their projects.Pi-Star can be what ever you want it to be, from a simple single mode hotsport running simplex providing you with access to the increasing number of Digital Voice networks, up to a public duplex multimode repeater!
See also RV
- https://en.wikipedia.org/wiki/Radio_control - the use of radio signals to remotely control a device. Radio control is used for control of model vehicles from a hand-held radio transmitter. Industrial, military, and scientific research organizations make use of radio-controlled vehicles as well.
- OpenSesame is a device that can wirelessly open virtually any fixed-code garage door in seconds, exploiting a new attack I've discovered on wireless fixed-pin devices. Using a child's toy from Mattel.
- https://github.com/jontio/libaeroambe - an mini-m decoder library.
- https://en.wikipedia.org/wiki/Radiosonde - battery-powered telemetry instrument carried into the atmosphere usually by a weather balloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. Modern radiosondes measure or calculate the following variables: altitude, pressure, temperature, relative humidity, wind (both wind speed and wind direction), cosmic ray readings at high altitude and geographical position (latitude/longitude). Radiosondes measuring ozone concentration are known as ozonesondes. Radiosondes may operate at a radio frequency of 403 MHz or 1680 MHz. A radiosonde whose position is tracked as it ascends to give wind speed and direction information is called a rawinsonde ("radar wind -sonde"). Most radiosondes have radar reflectors and are technically rawinsondes. A radiosonde that is dropped from an airplane and falls, rather than being carried by a balloon is called a dropsonde. Radiosondes are an essential source of meteorological data, and hundreds are launched all over the world daily.
- UKHAS Wiki: guides:tracking_guide
- https://en.wikipedia.org/wiki/Telegraph_key - a switching device used primarily to send Morse code. Similar keys are used for all forms of manual telegraphy, such as in ‘wire’ or electrical telegraph and ‘wireless’ or radio telegraphy.
- YouTube: Iambic Keyer and Technique. CW Morse Code key - left for dot, right for dash, allows repetitions if either is held
- https://en.wikipedia.org/wiki/Q_code a standardized collection of three-letter codes all of which start with the letter "Q". It is a brevity code initially developed for commercial radiotelegraph communication and later adopted by other radio services, especially amateur radio. To distinguish the use of "Q" codes transmitted as questions from those transmitted as statements, operators used the Morse question "INT" (dit dit dah dit dah) as a prefix to the "Q" code. Although Q codes were created when radio used Morse code exclusively, they continued to be employed after the introduction of voice transmissions. To avoid confusion, transmitter call signs are restricted; no country is ever issued an ITU prefix starting with "Q". Codes in the range QAA–QNZ are reserved for aeronautical use; QOA–QQZ for maritime use and QRA–QUZ for all services. "Q" has no official meaning, but it is sometimes assigned with a word with mnemonic value, such as "Queen's" (e.g. QFE = Queen's Field Elevation), "Query", "Question", or "reQuest".
Automatic Identification System
- https://en.wikipedia.org/wiki/AIS-SART - a self-contained radio device used to locate a survival craft or distressed vessel by sending updated position reports using a standard Automatic Identification System (AIS) class-A position report. The position and time synchronization of the AIS-SART are derived from a built in GNSS receiver (e.g. GPS). Shipboard Global Maritime Distress Safety System (GMDSS) installations include one or more search and rescue locating devices. These devices may be either an AIS-SART (AIS Search and Rescue Transmitter) (from January 1, 2010), or a radar-SART (Search and Rescue Transponder).
- https://en.wikipedia.org/wiki/Automatic_link_establishment - commonly known as ALE, is the worldwide de facto standard for digitally initiating and sustaining HF radio communications. ALE is a feature in an HF communications radio transceiver system that enables the radio station to make contact, or initiate a circuit, between itself and another HF radio station or network of stations. The purpose is to provide a reliable rapid method of calling and connecting during constantly changing HF ionospheric propagation, reception interference, and shared spectrum use of busy or congested HF channels.
- https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System - an amateur radio-based system for real time digital communications of information of immediate value in the local area. Data can include object Global Positioning System (GPS) coordinates, weather station telemetry, text messages, announcements, queries, and other telemetry. APRS data can be displayed on a map, which can show stations, objects, tracks of moving objects, weather stations, search and rescue data, and direction finding data. In its most widely used form, APRS is transported over the AX.25 protocol using 1200 bit/s Bell 202 AFSK on frequencies located within the 2 meter amateur band.
- aprs.fi map - The positions of the amateur radio operators and their vehicles are received from the APRS-IS network on the Internet. Most of them are originally transmitted on amateur radio frequencies (typically around 145 MHz), and received and forwarded to the APRS-IS by igate stations run by clubs and individuals around the world. The positions of ships are received from the AIS frequencies by receiving stations around the world. If you wish to receive AIS transmissions and provide them to the service, you're more than welcome to do so.
- https://github.com/flok99/MyAPRS - An program that sends APRS messages containing the current GPS location, retrieved from gpsd
- https://github.com/tailwheeldriver/APRS_Transciever - Design for a complete 2 meter band transciever, designed around the DRA818U/V and the arduino
- https://github.com/josefmtd/lora-aprs - APRS LoRa
- https://github.com/markqvist/MicroAPRS - an APRS firmware for MicroModem. It supports both normal KISS mode, and a simple serial protocol for easy communication with an Arduino, or other MCU.
- https://en.wikipedia.org/wiki/ACARS - an acronym for aircraft communications addressing and reporting system) is a digital datalink system for transmission of short messages between aircraft and ground stations via airband radio or satellite. The protocol was designed by ARINC and deployed in 1978, using the Telex format. More ACARS radio stations were added subsequently by SITA.
- JAERO - a program that demodulates and decodes Classic Aero ACARS (Aircraft Communications Addressing and Reporting System) messages sent from satellites to Aeroplanes (SatCom ACARS) commonly used when Aeroplanes are beyond VHF range. Demodulation is performed using the soundcard. Such signals are typically around 1.5Ghz and can be received with a simple low gain antenna that can be home brewed in a few hours in conjunction with a cheap RTL-SDR dongle.
- https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software) - pronounced "whisper", stands for "Weak Signal Propagation Reporter". It is a protocol, implemented in a computer program, used for weak-signal radio communication between amateur radio operators. The protocol was designed, and a program written initially, by Joe Taylor, K1JT. Software is now open source and is developed by a small team. The program is designed for sending and receiving low-power transmissions to test propagation paths on the MF and HF bands.
WSPR implements a protocol designed for probing potential propagation paths with low-power transmissions. Transmissions carry a station's callsign, Maidenhead grid locator, and transmitter power in dBm. The program can decode signals with S/N as low as −28 dB in a 2500 Hz bandwidth. Stations with internet access can automatically upload their reception reports to a central database called WSPRnet, which includes a mapping facility.
- WSPRnet - a group of amateur radio operators using K1JT's MEPT_JT digital mode to probe radio frequency propagation conditions using very low power (QRP/QRPp) transmissions. The software is open source, and the data collected are available to the public through this site.
- https://github.com/threeme3/WsprryPi - Makes a very simple WSPR beacon from your RasberryPi by connecting GPIO port to Antanna (and LPF), operates on LF, MF, HF and VHF bands from 0 to 250 MHz.
- https://github.com/biemster/fl2k-wspr - WSPR tx for osmo-fl2k
- https://en.wikipedia.org/wiki/Low-rate_picture_transmission - LRPT, is a digital transmission system, intended to deliver images and data from an orbital weather satellite directly to end users via a VHF radio signal. It is used aboard polar-orbiting, near-Earth weather satellite programs such as MetOp and NPOESS.
- https://en.wikipedia.org/wiki/Radio_Data_System - a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardizes several types of information transmitted, including time, station identification and program information.The standard began as a project of the European Broadcasting Union (EBU), but has since become an international standard of the International Electrotechnical Commission (IEC). Radio Broadcast Data System (RBDS) is the official name used for the U.S. version of RDS. The two standards are only slightly different.Both carry data at 1,187.5 bits per second on a 57 kHz subcarrier, so there are exactly 48 cycles of subcarrier during every data bit. The RBDS/RDS subcarrier was set to the third harmonic of the 19 kHz FM stereo pilot tone to minimize interference and intermodulation between the data signal, the stereo pilot and the 38 kHz DSB-SC stereo difference signal. (The stereo difference signal extends up to 38 kHz + 15 kHz = 53 kHz, leaving 4 kHz for the lower sideband of the RDS signal.) The data is sent with error correction. RDS defines many features including how private (in-house) or other undefined features can be "packaged" in unused program groups.
- RDS Surveyor — Radio Data System decoder - a complete open-source tool for decoding and analyzing Radio Data System (RDS) data. RDS (also known as RBDS in North America) is a communication protocol for embedding streams of digital information in FM radio broadcasts.RDS Surveyor is Java-based, hence it runs on all platforms. It has been successfully used on Linux, MacOS and Windows.
SCA / SCMO
- https://en.wikipedia.org/wiki/Subsidiary_communications_authority - the United States, and Subsidiary Communications Multiplex Operation (SCMO) in Canada, is a subcarrier on a radio station, allowing the station to broadcast additional services as part of its signal.
- https://en.wikipedia.org/wiki/Q15X25 - 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.
- https://en.wikipedia.org/wiki/Radiofax - also known as weatherfax (portmanteau word from the words "weather facsimile") and HF fax (due to its common use on shortwave radio), is an analogue mode for transmitting monochrome images. It was the predecessor to slow-scan television (SSTV). Prior to the advent of the commercial telephone line "fax" machine, it was known, more traditionally, by the term "radiofacsimile". The cover of the regular NOAA publication on frequencies and schedules states "Worldwide Marine Radiofacsimile Broadcast Schedules".
- https://en.wikipedia.org/wiki/Radioteletype - a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations connected by radio rather than a wired link. These machines were superseded by personal computers (PCs) running software to emulate teleprinters. 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 computers running teleprinter emulation software. The term radioteletype is used to describe both the original radioteletype system, sometimes described as "Baudot", as well as the entire family of systems connecting two or more teleprinters or PCs using software to emulate teleprinters, over radio, regardless of alphabet, link system or modulation.In some applications, notably military and government, radioteletype is known by the acronym RATT (Radio Automatic Teletype).
- https://en.wikipedia.org/wiki/Phase-shift_keying - a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and Bluetooth communication.
- Phase Shift Keying (PSK) - Signal Identification Wiki - a digital amateur radio mode based on Phase-Shift Keying (PSK) modulation. Most commonly used in HF, rarely seen at higher frequencies.
- - 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 also concentrates the RF energy[citation needed in a very narrow space thus allowing relatively low-power equipment (25 watts) to communicate globally using the same skywave propagation used by shortwave radio stations.
- bpsk31.com - a digital communication mode for amateur radio. It is one of the most common and easy-to-use digital modes as a PSK31 station needs only to consist of an SSB transceiver, an antenna, and a soundcard equipped PC.This website is a basic resource covering what is PSK31, how to set up and operate your own station, some available software, and additional resources.We also operate an email discussion list as a community resource where you can ask questions of other Hams and generally discuss anything related to PSK31.
- https://en.wikipedia.org/wiki/PSK63 - meaning Phase Shift Keying at a rate of 63 baud) is a digital radio modulation mode used primarily in the amateur radio field to conduct real-time keyboard-to-keyboard informal text chat between amateur radio operators.
- https://github.com/biemster/fl2k-psk - PSK tx for osmo-fl2k
- https://en.wikipedia.org/wiki/Packet_radio - a form of packet switching technology used to transmit digital data via wireless communications. Packet radio uses the same concepts of data transmission using datagrams that are fundamental to communications on the Internet, as opposed to older techniques used by dedicated or switched circuits. Packet radio can be used over long distances without the need for a physical connection between stations. Packet radio can also be used for mobile communications.
- https://github.com/wb2osz/direwolf - a software "soundcard" AX.25 packet modem/TNC and APRS encoder/decoder. It can be used stand-alone to observe APRS traffic, as a tracker, digipeater, APRStt gateway, or Internet Gateway (IGate).
- https://github.com/EliasOenal/multimon-ng - The successor of multimon. It decodes several digital transmission modes.
- https://en.wikipedia.org/wiki/AX.25 - a data link layer protocol originally derived from layer 2 of the X.25 protocol suite and designed for use by amateur radio operators. It is used extensively on amateur packet radio networks.AX.25 v2.0 and later occupies the data link layer, the second layer of the OSI model. It is responsible for establishing link-layer connections, transferring data encapsulated in frames between nodes, and detecting errors introduced by the communications channel. As AX.25 is a pre-OSI-model protocol, the original specification was not written to cleanly separate into OSI layers. This was rectified with version 2.0 (1984), which assumes compliance with OSI level 2.
- https://github.com/brannondorsey/chattervox - An AX.25 packet radio chat protocol with support for digital signatures and binary compression. Like IRC over radio waves satellite. 
- https://en.wikipedia.org/wiki/Datacasting - the broadcasting of data over a wide area via radio waves. It most often refers to supplemental information sent by television stations along with digital television, but may also be applied to digital signals on analog TV or radio. It generally does not apply to data which is inherent to the medium, such as PSIP data which defines virtual channels for DTV or direct broadcast satellite systems; or to things like cable modem or satellite modem, which use a completely separate channel for data.
- https://en.wikipedia.org/wiki/Bluetooth - a wireless technology standard for exchanging data over short distances (using short-wavelength UHF radio waves in the ISM band from 2.400 to 2.485 GHz) from fixed and mobile devices, and building personal area networks (PANs). Invented by Dutch electrical engineer Jaap Haartsen, working for telecom vendor Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables.
- https://en.wikipedia.org/wiki/Bluetooth_Low_Energy - Bluetooth LE, colloquially BLE, formerly marketed as Bluetooth Smart) is a wireless personal area network technology designed and marketed by the Bluetooth Special Interest Group (Bluetooth SIG) aimed at novel applications in the healthcare, fitness, beacons, security, and home entertainment industries. Compared to Classic Bluetooth, Bluetooth Low Energy is intended to provide considerably reduced power consumption and cost while maintaining a similar communication range.Mobile operating systems including iOS, Android, Windows Phone and BlackBerry, as well as macOS, Linux, Windows 8 and Windows 10, natively support Bluetooth Low Energy. The Bluetooth SIG predicts that by 2018 more than 90% of Bluetooth-enabled smartphones will support Bluetooth Low Energy.
- Bluez - provides Linux support for the core Bluetooth layers and protocols. It is flexible, efficient and uses a modular implementation.
- https://linux.die.net/man/1/hcitool - used to configure Bluetooth connections and send some special command to Bluetooth devices. If no command is given, or if the option -h is used, hcitool prints some usage information and exits.
- l2ping - Send L2CAP echo request and receive answer
- https://github.com/ZeroChaos-/blue_sonar - A simple wrapper for l2ping which shows rssi
- https://github.com/greatscottgadgets/ubertooth - an open source wireless development platform suitable for Bluetooth experimentation. Ubertooth ships with a capable BLE (Bluetooth Smart) sniffer and can sniff some data from Basic Rate (BR) Bluetooth Classic connections.
- https://github.com/pwnieexpress/blue_hydra - a Bluetooth device discovery service built on top of the bluez library. BlueHydra makes use of ubertooth where available and attempts to track both classic and low energy (LE) bluetooth devices over time.
- https://en.wikipedia.org/wiki/Bluetooth_low_energy_beacon - hardware transmitters - a class of Bluetooth low energy (LE) devices that broadcast their identifier to nearby portable electronic devices. The technology enables smartphones, tablets and other devices to perform actions when in close proximity to a beacon. Bluetooth beacons use Bluetooth low energy proximity sensing to transmit a universally unique identifier picked up by a compatible app or operating system. The identifier and several bytes sent with it can be used to determine the device's physical location, track customers, or trigger a location-based action on the device such as a check-in on social media or a push notification.
- https://github.com/mgaved/Anchorholds - An Android app for finding BLE beacons and display related info
- http://stackoverflow.com/questions/12338621/a2dp-sink-without-pulseaudio - audio streaming
- https://github.com/Arkq/bluez-alsa - Bluetooth Audio ALSA Backend
- https://en.wikipedia.org/wiki/LoRa - a patented digital wireless data communication IoT technology developed by Cycleo of Grenoble, France, and acquired by Semtech in 2012. LoRa uses license-free sub-gigahertz radio frequency bands like 169 MHz, 433 MHz, 868 MHz (Europe) and 915 MHz (North America). LoRa enables very-long-range transmissions (more than 10 km in rural areas) with low power consumption. The technology is presented in two parts — LoRa, the physical layer and LoRaWAN, the upper layers.
New Packet Radio
- https://github.com/znuh/re-DECTed - tools for playing with DECT
- https://github.com/P1sec/QCSuper - a tool communicating with Qualcomm-based phones and modems, allowing to capture raw 2G/3G/4G radio frames, among other things.
- https://en.wikipedia.org/wiki/1G - refers to the first generation of wireless cellular technology (mobile telecommunications). These are the analog telecommunications standards that were introduced in the 1980s and continued until being replaced by 2G digital telecommunications. The main difference between the two mobile cellular systems (1G and 2G), is that the radio signals used by 1G networks are analog, while 2G networks are digital.
- https://en.wikipedia.org/wiki/2G - short for second-generation cellular technology. Second-generation 2G cellular networks were commercially launched on the GSM standard in Finland by Radiolinja (now part of Elisa Oyj) in 1991. Three primary benefits of 2G networks over their predecessors were that phone conversations were digitally encrypted; 2G systems were significantly more efficient on the spectrum allowing for far greater wireless penetration levels; and 2G introduced data services for mobile, starting with SMS text messages. 2G technologies enabled the various networks to provide the services such as text messages, picture messages, and MMS (multimedia messages). All text messages sent over 2G are digitally encrypted, allowing for the transfer of data in such a way that only the intended receiver can receive and read it.
- Building a portable GSM BTS using the Nuand bladeRF, Raspberry Pi and YateBTS (The Definitive and Step by Step Guide) 
- https://github.com/ptrkrysik/gr-gsm - based on the gsm-receiver written by Piotr Krysik (also the main author of gr-gsm) for the Airprobe project.The aim is to provide set of tools for receiving information transmitted by GSM equipment/devices.
- https://en.wikipedia.org/wiki/Wireless_Application_Protocol - a technical standard for accessing information over a mobile wireless network. A WAP browser is a web browser for mobile devices such as mobile phones that uses the protocol. Introduced with much hype in 1999, WAP achieved some popularity in the early 2000s, but by the 2010s it had been largely superseded by more modern standards. Most modern handset internet browsers now fully support HTML, so do not need to use WAP markup for webpage compatibility, and most of them are no longer able to render and display pages written in WAP.
- Kannel - a compact and very powerful open source WAP and SMS gateway, used widely across the globe both for serving trillions of short messages (SMS), WAP Push service indications and mobile internet connectivity.
- https://en.wikipedia.org/wiki/SMS - Short Message Service is a text messaging service component of most telephone, World Wide Web, and mobile device systems. It uses standardized communication protocols to enable mobile devices to exchange short text messages. An intermediary service can facilitate a text-to-voice conversion to be sent to landlines. SMS was the most widely used data application, with an estimated 3.5 billion active users, or about 80% of all mobile subscribers, at the end of 2010.
SMS, as used on modern devices, originated from radio telegraphy in radio memo pagers that used standardized phone protocols. These were defined in 1985 as part of the Global System for Mobile Communications (GSM) series of standards. The protocols allowed users to send and receive messages of up to 160 alpha-numeric characters to and from GSM mobiles. Although most SMS messages are mobile-to-mobile text messages, support for the service has expanded to include other mobile technologies, such as ANSI CDMA networks and Digital AMPS. SMS is also employed in mobile marketing, a type of direct marketing.According to one market research report, as of 2014, the global SMS messaging business was estimated to be worth over $100 billion, accounting for almost 50 percent of all the revenue generated by mobile messaging.
- https://en.wikipedia.org/wiki/Multimedia_Messaging_Service - a standard way to send messages that include multimedia content to and from a mobile phone over a cellular network. Users and providers may refer to such a message as a PXT, a picture message, or a multimedia message. The MMS standard extends the core SMS (Short Message Service) capability, allowing the exchange of text messages greater than 160 characters in length. Unlike text-only SMS, MMS can deliver a variety of media, including up to forty seconds of video, one image, a slideshow of multiple images, or audio.
- https://en.wikipedia.org/wiki/Rich_Communication_Services - a communication protocol between mobile-telephone carriers and between phone and carrier, aiming at replacing SMS messages with a text-message system that is richer, provide phonebook polling (for service discovery), and transmit in-call multimedia
- https://en.wikipedia.org/wiki/3G - standing for third generation, is the third generation of wireless mobile telecommunications technology. It is the upgrade for 2G and 2.5G GPRS networks, for faster internet speed. This is based on a set of standards used for mobile devices and mobile telecommunications use services and networks that comply with the International Mobile Telecommunications-2000 (IMT-2000) specifications by the International Telecommunication Union. 3G finds application in wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls and mobile TV.
3G telecommunication networks support services that provide an information transfer rate of at least 0.2 Mbit/s. Later 3G releases, often denoted 3.5G and 3.75G, also provide mobile broadband access of several Mbit/s to smartphones and mobile modems in laptop computers. This ensures it can be applied to wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls and mobile TV technologies.
- https://en.wikipedia.org/wiki/UMTS - The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the International Telecommunications Union IMT-2000 standard set and compares with the CDMA2000 standard set for networks based on the competing cdmaOne technology. UMTS uses wideband code division multiple access (W-CDMA) radio access technology to offer greater spectral efficiency and bandwidth to mobile network operators.UMTS specifies a complete network system, which includes the radio access network (UMTS Terrestrial Radio Access Network, or UTRAN), the core network (Mobile Application Part, or MAP) and the authentication of users via SIM (subscriber identity module) cards.The technology described in UMTS is sometimes also referred to as Freedom of Mobile Multimedia Access (FOMA) or 3GSM.Unlike EDGE (IMT Single-Carrier, based on GSM) and CDMA2000 (IMT Multi-Carrier), UMTS requires new base stations and new frequency allocations.
3.5G / HSPA
3.75G / HSPA+
3.95G / LTE
- https://en.wikipedia.org/wiki/LTE_(telecommunication) - a standard for wireless broadband communication for mobile devices and data terminals, based on the GSM/EDGE and UMTS/HSPA technologies. It increases the capacity and speed using a different radio interface together with core network improvements. The standard is developed by the 3GPP (3rd Generation Partnership Project) and is specified in its Release 8 document series, with minor enhancements described in Release 9. LTE is the upgrade path for carriers with both GSM/UMTS networks and CDMA2000 networks. The different LTE frequencies and bands used in different countries mean that only multi-band phones are able to use LTE in all countries where it is supported.
LTE is commonly marketed as "4G LTE and Advance 4G", but it does not meet the technical criteria of a 4G wireless service, as specified in the 3GPP Release 8 and 9 document series for LTE Advanced. LTE is also commonly known as 3.95G. The requirements were originally set forth by the ITU-R organization in the IMT Advanced specification. However, due to marketing pressures and the significant advancements that WiMAX, Evolved High Speed Packet Access and LTE bring to the original 3G technologies, ITU later decided that LTE together with the aforementioned technologies can be called 4G technologies. The LTE Advanced standard formally satisfies the ITU-R requirements to be considered IMT-Advanced. To differentiate LTE Advanced and WiMAX-Advanced from current 4G technologies, ITU has defined them as "True 4G".
- https://github.com/pgorczak/srslte-docker-emulated - Minimal end-to-end LTE. Dockerized and emulated radio over shared memory. 
- https://en.wikipedia.org/wiki/4G - the fourth generation of broadband cellular network technology, succeeding 3G. A 4G system must provide capabilities defined by ITU in IMT Advanced. Potential and current applications include amended mobile web access, IP telephony, gaming services, high-definition mobile TV, video conferencing, and 3D television. The first-release Long Term Evolution (LTE) standard (a 4G candidate system) has been commercially deployed in Oslo, Norway, and Stockholm, Sweden since 2009. It has, however, been debated whether first-release versions should be considered 4G.
- https://en.wikipedia.org/wiki/LTE_Advanced - a mobile communication standard and a major enhancement of the Long Term Evolution (LTE) standard. It was formally submitted as a candidate 4G to ITU-T in late 2009 as meeting the requirements of the IMT-Advanced standard, and was standardized by the 3rd Generation Partnership Project (3GPP) in March 2011 as 3GPP Release 10.
- Osmocom - an umbrella project regarding Open source mobile communications. This includes software and tools implementing a variety of mobile communication standards, including GSM, DECT, TETRA and others.
- Cellular Infrastructure - a group of Osmocom programs implementing cellular network infrastructure components for GSM, GPRS, EDGE, UMTS, HSPA, LTE and their associated interfaces and protocol stacks.
- OpenBTS - a Linux application that uses a software-defined radio to present a standard 3GPP air interface to user devices, while simultaneously presenting those devices as SIP endpoints to the Internet. This forms the basis of a new type of wireless network which promises to expand coverage to unserved and underserved markets while unleashing a platform for innovation, including offering support for emerging network technologies, such as those targeted at the Internet of Things.
- UmTRX - The industrial grade dual-channel wide-band SDR transceiver.
- UmSITE-TM3 - A complete mobile network in a single tower mounted base station, one of the key components of the Fairwaves GSM network architecture. Technical details: Osmocom or OpenBTS software suites (Osmocom by default). Ability to run GnuRadio and other SDR software. Output power - 3W per channel (6W total). UmSITE includes internal duplexers and amplifiers. 1-3 km coverage (with external antennas). Two independent TRX's, i.e. two ARFCNs. Based on UmTRX transceiver. Stable reference clocks: 26MHz TCXO (integer multiple of GSM sample rate) with 100ppb frequency stability. DAC for TCXO frequency fine tuning. Integrated GPS module for automatic TCXO frequency stabilization.
- ZeroPhone - an open-source smartphone that can be assembled for 50$ in parts. It is Linux-powered, with UI software written in Python, allowing it it to be easily modifiable - and it doesn't prohibit you from changing the way it works.
- MEGA65 - The 21st century realization of the C65 heritage: A complete 8-bit computer running around 50x faster than a C64 while being highly compatible. C65 design, mechanical keyboard, HD output, SD card support, Ethernet, extended memory and other features increase the fun without spoiling the 8-bit feel. Hardware designs and software are open-source (LGPL).
- http://wiki.opendigitalradio.org Opendigitalradio.org wiki] - Open digital broadcasting techniques based on software defined radio. Digital radio transmission and development must also become democratized for experimenters and small broadcasters. Opendigitalradio.org wiki is about creating a community for documenting and exchanging experimentations and gather information about existing small-scale DAB projects. Please read Introduction for more information. Opendigitalradio is a non-profit association based in Switzerland (page in french), offering also a broadcast infrastructure for temporary radio stations.
- FUNcube Dongle - originally designed with receiving signals from space
- Whitebox Handheld SDR - Low power, embeddable framework; inspired by cell phone and SDR architectures 
- Myriad RF is a family of open source hardware and software projects for wireless communications, and a community that is working to make wireless innovation accessible to as many people as possible.
- LimeSDR board provides a hardware platform for developing and prototyping high-performance and logic-intensive digital and RF designs using Altera’s Cyclone IV FPGA and Lime Microsystems transceiver.
- https://code.facebook.com/posts/1754757044806180/introducing-opencellular-an-open-source-wireless-access-platform 
- https://www.ettus.com/product/details/UB210-KIT - 70MHz to 6GHz
- http://sdr.osmocom.org/trac/wiki/rtl-sdr - RTL-SDR is a set of tools that enables DVB-T USB dongles based on the Realtek RTL2832U chipset to be used as cheap software defined radios, given that the chip allows transferring raw I/Q samples from the tuner straight to the host device.
The frequency range of the RTL2832U / E4000 is generally around 64MHZ to 1700MHz with a gap around 1100MHz to 1250MHz. The RTL2832U / R820T frequency range is 24MHZ to roughly 1850MHz with no gaps (found yet), and no DC offset spike.
RTL dongles have 2.4 MHz of useful bandwidth.
- YouTube: Decode APRS with RTL SDR (RTL2832U)
- Rtl Power - a unix-hacker's approach to the waterfall. Its unique features include:Just getting started with rtl_power, and it looks like just the to... Unlimited frequency range. You can do the whole 1.7GHz of a dongle. Unlimited time. At least until you run out of disk for logging. Unlimited FFT bins. But in practice I don't think I've taken it above 100k bins. Quantitative rendering. Exact power levels are logged. Runs on anything. A slower computer will use less samples to keep up.
- https://github.com/jorisvr/SoftFM - Software decoder for FM broadcast radio with RTL-SDR
- https://github.com/jj1bdx/ngsoftfm-jj1bdx - a command line software decoder for FM broadcast radio with stereo support (forked SoftFM)
- Multi-RTL - Making multiple channels receiver from cheap RTL-SDR dongles
Broadcom Wi-Fi chips
- https://github.com/seemoo-lab/mobisys2018_nexmon_software_defined_radio - This projects demonstrates our discovery that turns Broadcom's 802.11ac Wi-Fi chips into software-defined radios that transmit arbitrary signals in the Wi-Fi bands. In this example, we patch the Wi-Fi firmware of BCM4339 devices installed in Nexus 5 smartphones and BCM43455c0 devices installed in Raspberry Pi B3+ computers. The Raspberry Pi B3 will never be supported as it only contains an 802.11n PHY. The firmware patch utilises three ioctls. 
- Turning the Raspberry Pi Into an FM Transmitter - Imperial College Robotics Society -   
- Make: Raspberry Pirate Radio 
- https://github.com/Make-Magazine/PirateRadio - MAKE Raspberry Pi Automated FM Radio Script.
- https://github.com/F5OEO/rpitx - RF transmitter for Raspberry Pi
- https://github.com/felixzero/rpitx_alsa - An ALSA sound driver interface for sending samples to F5OEO's rpitx. This is only a proof-of-concept demo. It should work, but it is in no way complete and/or perfect.
- https://github.com/clemibunge/rpitx_GUI_tx - GUI for rpitx
- https://github.com/ChristopheJacquet/PiFmRds - FM-RDS transmitter using the Raspberry Pi's PWM
- https://github.com/coup-de-foudre/tesla_coil_fm_driver - Project forked from PNPtutorials.Use Raspberry Pi as FM transmitter. Works on any RPi board.This project uses the general clock output to produce frequency modulated radio communication. It is based on idea originaly posted here but does not use DMA controller in order to distribute samples to output (clock generator), so sound quality is worse as in PiFm project and only mono transmition is available but this makes possible to run it on all kind of boards.
- PiAmp - Raspberry Pi FM transmitter amp and filter
- osmo-fl2k - Since rtl-sdr has been released a couple of years ago, cheap SDR receivers are ubiquitous. SDRs with transmission capability have become cheaper as well, but are still more expensive. osmo-fl2k allows to use USB 3.0 to VGA adapters based on the Fresco Logic FL2000 chip, which are available for around $5, as general purpose DACs and SDR transmitter generating a continuous stream of samples by avoiding the HSYNC and VSYNC blanking intervals.
- media.ccc.de - osmo-fl2k - the -evil- transmit-side brother of RTL-SDR
- https://github.com/steve-m/fl2k-examples - example flowgraphs for osmo-fl2k. These perform offline computation of samples which then can be transmitted with fl2k_file.
- https://github.com/peterbmarks/fl2k - Playing with cheap VGA dongles as a digital to analog converter for ham radio
- The Rise and Fall of Pulses | Hackaday.io
- https://github.com/tedyapo/arbitrary-waveform-generator - This python module lets you define synchronized waveforms and sample them to be output through a multi-channel DAC. So far, the code maily targets the the FL2k USB-to-VGA dongle using osmo-fl2k software, although the code could easily be modifed to output other formats. At the moment, the output is in an 8-bit signed format for use with osmo-fl2k.
- AM Band Voice Frequency Marker | Hackaday.io
running the "volk_profile" gnuradio utility will detect and enable processor specific optimisations and will in many cases give a significant performance boost.
- Gqrx is a software defined radio receiver powered by the GNU Radio SDR framework and the Qt graphical toolkit.
- LuaRadio is a lightweight, embeddable flow graph signal processing framework for software-defined radio. It provides a suite of source, sink, and processing blocks, with a simple API for defining flow graphs, running flow graphs, creating blocks, and creating data types. 
- liquid-dsp - a free and open-source signal processing library for software-defined radios written in C. Its purpose is to provide a set of extensible DSP modules that do not rely on external dependencies or cumbersome frameworks.
- CubicSDR - Cross-Platform and Open-Source Software Defined Radio Application
- FreeDV - a Digital Voice mode for HF radio. You can run FreeDV using a free GUI application for Windows, Linux and OSX that allows any SSB radio to be used for low bit rate digital voice.
- https://github.com/JvanKatwijk/wfm-rpi - simple FM receiver for use on (a.o) on a Raspberry PI 2
- https://github.com/f4exb/sdrangel - SDR Rx/Tx software for Airspy, Airspy HF+, BladeRF, HackRF, LimeSDR, PlutoSDR, RTL-SDR, SDRplay RSP1, XTRX and FunCube
- https://github.com/JvanKatwijk/swradio-8 - shortwave receiver for use with sdrplay, hackrf, dabsticks and pmsdr
- https://github.com/JvanKatwijk/xxx-radio - very simple fm/am receiver software for use with sdrplay or airspy
- https://github.com/xmikos/qspectrumanalyzer - Spectrum analyzer for multiple SDR platforms (PyQtGraph based GUI for soapy_power, hackrf_sweep, rtl_power, rx_power and other backends)
- https://github.com/miek/inspectrum - Offline radio signal analyser
- https://github.com/jontio/JMPX - A Stereo encoder for FM transmitters now with RDS, SCA and DSCA support.
https://github.com/tedyapo/serial-port-sdr - Experimental software-defined radio using a serial port
- welle.io - an open source DAB and DAB+ software defined radio (SDR) with support for rtl-sdr (RTL2832U) and airspy. It supports high DPI and touch displays and it runs even on cheap computers like Raspberry Pi 2/3 and 100€ China Windows 10 tablets.
- https://github.com/JvanKatwijk/qt-dab - for Windows, Linux and Raspberry Pi for listening to terrestrial Digital Audio Broadcasting (DAB and DAB+). It is the successor of both DAB-rpi and sdr-j-DAB, two former programs by the same author.
- https://github.com/JvanKatwijk/dabradio - little brother of Qt-DAB for use under Linux-x64, Windows and RPI2/3
- https://github.com/JvanKatwijk/dab-cmdline - provides entries for the functionality to handle DAB/DAB+ through some simple calls. A few callback functions provide the communication back from the library to the caller. The library interface is given in dab-api.h
- https://github.com/JvanKatwijk/dab-server - simple dab-server with android client as remote control over bluetooth
- Google Play: Wavesink DAB/FM Trial - Turn your phone or tablet into a DAB and FM-Stereo RDS receiver. On USB-OTG compatible phones, simply connect a cheap USB dongle and listen to VHF radio in HiFi quality. Note that the trial version has a runtime limitation and does not support DAB+ but only DAB and FM/RDS.
- Identification Guide - wiki intended to help identify radio signals through example sounds and waterfall images. Most signals are received and recorded using a software defined radio such as the RTL-SDR, Airspy, SDRPlay, HackRF, BladeRF, Funcube Dongle, USRP or others.
- OpenBTS - a Unix application that uses a software radio to present a GSM air interface to standard 2G GSM handset and uses a SIP softswitch or PBX to connect calls. (You might even say that OpenBTS is a simplified form of IMS that works with 2G feature-phone handsets.) The combination of the global-standard GSM air interface with low-cost VoIP backhaul forms the basis of a new type of cellular network that can be deployed and operated at substantially lower cost than existing technologies in many applications, including rural cellular deployments and private cellular networks in remote areas.
- SDR.hu - On sdr.hu, you can find SDR receivers that amateur radio operators shared, so you can listen to radio signals without even having to buy any SDR hardware! In fact, amateur radio is a great thing and also lets you experiment with transmitting on the air, by using various frequency bands and modulations.
- SDR.hu - a multi-user SDR receiver software with a web interface.
- RootIO Radio - a technology platform for low cost, hyperlocal community radio stations. Tiny FM radio stations that require little investment, maintenance, or contribution from the community, yet at the same time offer more and better modes of interaction than traditional stations. After a few days of installation and training, stations can start to facilitate new economic opportunities, new opportunities for expression and deliberation, and provide information across, into, and out of the community they serve.Each station is amplified by our cloud/telephony Radio as a Service (RaaS). With the cloud, an individual station can receive free voice-quality calls that go straight to air, download audio from the Internet in the background, or run SMS votes. Using any basic phone (through RaaS) local hosts can run live shows with callers; local business people can record ads or announcements; citizen journalists can cover live meetings or sports events. With solar power a station can serve as 24/7 endpoint to emergency services.Four stations have been running in Northern Uganda for the last year, and small rural communities are creating their own programs, reporting their own news, and requesting audio content from the Internet. RootIO, with the help of Resilient Africa Network, is hoping to launch another 20 stations in the coming year.
- RadioWitness - Immutable, peer-to-peer archiving and distribution of police radio calls. Authors use Software-Defined Radios and Dat Archives to record local police radio. Publishers seed archives from Authors and then re-distribute them to larger audiances. Other rolse arise too, such as Studios who synthesize radio archives into archives of audible speech, and Indexers who aggregate metadata on individual radio calls. Stop by #radiowitness on freenode and say hi.
- Open Broadcaster - Broadcast Automation Software LPFM IPTV
- https://en.wikipedia.org/wiki/Radio-frequency_identification - uses electromagnetic fields to automatically identify and track tags attached to objects. The tags contain electronically stored information. Passive tags collect energy from a nearby RFID reader's interrogating radio waves. Active tags have a local power source (such as a battery) and may operate hundreds of meters from the RFID reader. Unlike a barcode, the tag need not be within the line of sight of the reader, so it may be embedded in the tracked object. RFID is one method of automatic identification and data capture (AIDC).
- https://en.wikipedia.org/wiki/Microchip_implant_(animal) - an identifying integrated circuit placed under the skin of an animal. The chip, about the size of a large grain of rice, uses passive RFID (Radio Frequency Identification) technology, and is also known as a PIT (Passive Integrated Transponder) tag.Externally attached microchips such as RFID ear tags are commonly used to identify farm and ranch animals, with the exception of horses. Some external microchips can be read with the same scanner used with implanted chips.
- https://github.com/Proxmark/proxmark3 - a powerful general purpose RFID tool, the size of a deck of cards, designed to snoop, listen and emulate everything from Low Frequency (125kHz) to High Frequency (13.56MHz) tags.This repository contains enough software, logic (for the FPGA), and design documentation for the hardware that you could, at least in theory, do something useful with a proxmark3.