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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.

🔗 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.