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🔗 Physics 🔗 Meteorology 🔗 Radio

A whistler is a very low frequency or VLF electromagnetic (radio) wave generated by lightning. Frequencies of terrestrial whistlers are 1 kHz to 30 kHz, with a maximum amplitude usually at 3 kHz to 5 kHz. Although they are electromagnetic waves, they occur at audio frequencies, and can be converted to audio using a suitable receiver. They are produced by lightning strikes (mostly intracloud and return-path) where the impulse travels along the Earth's magnetic field lines from one hemisphere to the other. They undergo dispersion of several kHz due to the slower velocity of the lower frequencies through the plasma environments of the ionosphere and magnetosphere. Thus they are perceived as a descending tone which can last for a few seconds. The study of whistlers categorizes them into Pure Note, Diffuse, 2-Hop, and Echo Train types.

Voyager 1 and 2 spacecraft detected whistler-like activity in the vicinity of Jupiter known as "Jovian Whistlers", implying the presence of lightning there.

🔗 Radio

Digital Radio Frequency Memory (DRFM) is an electronic method for digitally capturing and retransmitting RF signals. DRFM systems are typically used in radar jamming, although applications in cellular communications are becoming more common.

🔗 Technology 🔗 Physics 🔗 Radio 🔗 Astronomy 🔗 Engineering

In engineering, the terahertz gap is a frequency band 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 unfeasible.

Mass production of devices in this range and operation at room temperature (at which energy k·T is equal to the energy of a photon with a frequency of 6.2 THz) are mostly impractical. This leaves a gap between mature microwave technologies in the highest frequencies of the radio spectrum and the well developed optical engineering of infrared detectors in their lowest frequencies. This radiation is mostly used in small-scale, specialized applications such as submillimetre astronomy. Research that attempts to resolve this issue has been conducted since the late 20th century.

🔗 Mexico 🔗 Radio

A border blaster is a broadcast station that, though not licensed as an external service, is, in practice, used to target another country. The term "border blaster" is of North American origin, and usually associated with Mexican AM stations whose broadcast areas cover large parts of the United States, and United States border AM stations covering large parts of Canada. Conceptually similar European broadcasting included some pre-World War II broadcasting towards the United Kingdom, "radio périphérique" around France and the U.S. government-funded station Radio Free Europe, targeting European countries behind the Iron Curtain.

With broadcasting signals far more powerful than those of U.S. stations, the Mexican border blasters could be heard over large areas of the U.S. from the 1940s to the 1970s, often to the great irritation of American radio stations, whose signals could be overpowered by their Mexican counterparts. These are also sometimes referred to as X stations for their call letters: Mexico assigns callsigns beginning with XE or XH to broadcast stations.

On November 9, 1972, in Washington, D.C., the United States and Mexico signed an "Agreement Concerning Frequency Modulation Broadcasting in the 87.5 to 108 MHz Band". Since then, in the FM band power levels and frequency assignments have been set by mutual agreement between the two countries. AM radio border blasters still exist, though they are largely ignored due to the decline of AM radio in the U.S. and in Mexico. There are several such stations licensed by Mexico's Secretariat of Communications and Transportation using transmitters with an effective radiated power similar to those of major licensed commercial stations located within the U.S.

🔗 United States 🔗 Law 🔗 Radio

The Brinkley Act is the popular name given to 47 U.S.C. § 325(c) (originally section 325(b) of the Communications Act of 1934). This provision was enacted by the United States Congress to prohibit broadcasting studios in the U.S. from being connected by live telephone line or other means to a transmitter located in Mexico.

Prior to World War II, Dr. John R. Brinkley controlled a high-power radio station, XERA, located in Ciudad Acuña, Coahuila (Acuna City), on the U.S.-Mexican border, across the Rio Grande from Del Rio, Texas. The programs on Brinkley's stations originated from studios in the US, which were connected to his transmitters via international telephone lines. Brinkley ran a popular but controversial program offering questionable medical advice to his listeners. Since Brinkley's transmitters were licensed in Mexico, which at the time had very limited regulation of broadcast content, his broadcasting licenses could not be directly threatened by the US government.

Dr. Brinkley's activities at his studio were thought to be a local matter, outside Congress's regulatory powers. However, the communications between the studio and his transmitters clearly involved international commerce and were therefore within Congress's power to regulate under the Commerce Clause. The operative language is as follows:

No person shall be permitted to locate, use, or maintain a radio broadcast studio or other place or apparatus from which or whereby sound waves are converted into electrical energy, or mechanical or physical reproduction of sound waves produced, and caused to be transmitted or delivered to a radio station in a foreign country for the purpose of being broadcast from any radio station there having a power output of sufficient intensity and/or being so located geographically that its emissions may be received consistently in the United States, without first obtaining a permit from the Commission upon proper application therefor.

The law goes on (47 U.S.C. § 325(d)) to state that the legal process for requesting such a permit is the same as that for requesting or renewing a license for a domestic station.

Although the original purpose of the Brinkley Act was to shut down a broadcaster, such applications are today granted as a matter of course, and a number of US broadcasters are permitted to program Mexican stations from their US studios in communities such as San Diego, California and Brownsville, Texas, where as many as a third of the stations in each radio market are licensed in Mexico. In recent years the law has returned to prominence, as its provisions have been used to extend US ownership limits to Mexican stations leased by US broadcasters.