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Carrier current

From Wikipedia, the free encyclopedia

Carrier current transmission, originally called wired wireless, employs guided low-power radio-frequency signals, which are transmitted along electrical conductors. The transmissions are picked up by receivers that are either connected to the conductors, or a short distance from them. Carrier current transmission is used to send audio and telemetry to selected locations, and also for low-power broadcasting that covers a small geographical area, such as a college campus. The most common form of carrier current uses longwave or medium wave AM radio signals that are sent through existing electrical wiring, although other conductors can be used, such as telephone lines.

Technology

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Carrier current generally uses low-power transmissions. In cases where the signals are being carried over electrical wires, special preparations must be made for distant transmissions, as the signals cannot pass through standard utility transformers. Signals can bridge transformers if the utility company has installed high-pass filters, which typically has already been done when carrier current-based data systems are in operation. Signals can also be impressed onto the neutral leg of the three-phase electric power system, a practice known as "neutral loading", in order to reduce or eliminate mains hum (60 hertz in North American installations), and to extend effective transmission line distance.

For a broadcasting installation, a typical carrier current transmitter has an output in the range 5 to 30 watts. However, electrical wiring is a very inefficient antenna, and this results in a transmitted effective radiated power of less than one watt, and the distance over which signals can be picked up is usually less than 60 meters (200 feet) from the wires. Transmission sound quality can be good, although it sometimes includes the low-frequency mains hum interference produced by the alternating current. However, not all listeners notice this hum, nor is it reproduced well by all receivers.

Extensive systems can include multiple unit installations with linear amplifiers and splitters to increase the coupling points to a large electrical grid (whether a campus, a high-rise apartment or a community). These systems would typically require coaxial cable interconnection from a transmitter to the linear amplifiers. In the 1990s, LPB, Inc., possibly the largest manufacturer of these transmission systems, designed and supplied several extensive campus-based systems that included fiber-optic links between linear amplifiers to prevent heterodyne interference.

Initial development

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The ability for electrical conductors to act as waveguides for radio signals was noted in the earliest days of radio experimentation, and Heinrich Hertz published the first review of the phenomenon in 1889.[1] By 1911, Major General George Owen Squier was conducting some of the earliest studies designed to put carrier current transmissions, which he called "wired wireless", to practical use.[2] To be effective, the radio transmitter must be capable of generating pure continuous-wave AM transmissions. Thus, the technology needed to set up carrier current transmissions would not be readily available until the late 1910s, with the development of vacuum tube transmitters and amplifiers.

Long-distance communication

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The first commercial applications of carrier current technology included the setting up of long-distance telegraph, telemetry, and telephone communication by electrical companies over their high-voltage distribution lines. This approach had a major advantage over standard telegraph and telephone lines, because radio signals can readily jump over any small gaps in cases when there is a line break. In May 1918, the Imperial Japanese Electro-Technical Laboratory of Tokyo successfully tested "wave telephony" over the Kinogawa Hydro-Electric Company's 144-kilometer (90-mile) long power line.[3] In the summer of 1920, a successful test transmission over 19.2 kilometers (12 miles) of high-tension wires was reported from New Jersey,[4] and by 1929, 1,000 installations had been made in the United States and Europe.[3] The majority of power line communication installations use transmissions in the longwave band, to avoid interference to and from standard AM stations.

Home entertainment services

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United States

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In 1923, the Wired Radio Service Company, a subsidiary of the local electric company, set up a subscription news and entertainment service at Staten Island, New York that used carrier current transmissions over the electrical power lines. To receive the transmissions, subscribers had to lease a receiver costing between two and five dollars a month.[5] However, despite the power company's optimism that the system would eventually be installed nationally, the effort proved unable to compete with the free offerings provided by standard radio stations. General Squier continued to unsuccessfully promote the technology for home entertainment, until 1934, when he helped found the Muzak company, which focused on the business market.

Europe

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Carrier current home entertainment services would prove to be more popular in Europe. Previously, there had been a few successful telephone newspaper services, which sent entertainment to subscribers over standard telephone lines. However, carrier current transmissions had the ability to provide programs over telephone lines without affecting the regular telephone service, and could also send multiple programs simultaneously.

In Germany, the carrier current service was called Drahtfunk, and in Switzerland Telefonrundspruch. In the Soviet Union, this approach was very common beginning in the 1930s because of its low cost and accessibility, and because it made reception of uncensored over-the-air transmissions more difficult. In Norway radiation from power lines was used, provided by the Linjesender facility. In Britain such systems were used for a time in areas where reception from conventional BBC radio transmitters was poor.

In these systems programs were fed by special transformers into the lines. To prevent uncontrolled propagation, filters for the service's carrier frequencies were installed in substations and at line branches. Systems using telephone wires were incompatible with ISDN which required the same bandwidth to transmit digital data. Although the Swiss and German systems have been discontinued, the Italian it:Filodiffusione still has several hundred thousand subscribers.

Programs formerly carried by "wire broadcasting" in Switzerland included:

  • 175 kHz Swiss Radio International
  • 208 kHz RSR1 "la première" (French)
  • 241 kHz "classical music"
  • 274 kHz RSI1 "rete UNO" (Italian)
  • 307 kHz DRS 1 (German)
  • 340 kHz "easy music"

Low-power broadcasting stations

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Carrier current technology is also used for broadcasting radio programs that can be received over a small area by standard AM radios. This is most often associated with college radio and high school radio, but also has applications for hospital radio stations and at military bases, sports stadiums, convention halls, mental and penal institutions, trailer parks, summer camps, office buildings, and drive-in movie theaters. Transmitters that use carrier current are very simple, making them an effective option for students interested in radio.

Carrier current broadcasting began in 1936, when students at Brown University in Providence, Rhode Island developed a carrier current station initially called "The Brown Network". This station was founded by George Abraham[6] and David W. Borst,[7] who had originally installed an intercom system between their dormitory rooms. The intercom links were first expanded to additional locations, and then the system was replaced by distributed low-powered radio transmitters, which fed their signals into various buildings' electrical wires, allowing nearby radio receivers to receive the transmissions.[8]

The carrier current station idea soon spread to other college campuses, especially in the northeastern United States. The Intercollegiate Broadcasting System (IBS) was formed in February 1940, to coordinate activities between twelve college carrier current stations and to solicit advertisers interested in sponsoring programs geared toward their student audiences.[9] The innovation received a major publicity boost by a complimentary article that appeared in the May 24, 1941 issue of The Saturday Evening Post,[10] and eventually hundreds of college stations were established. Responding to the growing phenomenon, a 1941 release issued by the U.S. Federal Communications Commission (FCC) stated that because of the stations' very limited ranges, it had "not promulgated any rule governing their operation."[11] Therefore, to operate legally, U.S. carrier current station broadcast emissions must adhere to the FCC's Title 47 CFR Part 15 Rules for unlicensed transmissions.[12]

Educational institution carrier current and cablecast stations

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Many college stations that went on to obtain FM broadcasting licenses started out as carrier current stations because of the low cost and relative ease of starting one. Although college-based carrier current stations have existed for over 80 years, their numbers are steadily declining, becoming supplemented, or replaced, by other transmission methods, including low-power FM (LPFM), closed circuit over cable TV channels, and Internet streaming audio and video, along with simple PowerPoint presentations of college campus news and information being streamed using low-cost consumer televisions and monitors. As with most other student-run facilities, these stations often operate on sporadic schedules.

In the United States, unlike educational FM stations, carrier current stations can carry a full range of advertising. Due to their low power, these stations do not require an FCC license, and are not assigned an official call sign. However, in keeping with standard radio industry practice, they commonly adopt their own call sign-like identifiers.

Existing stations

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Former stations

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See also

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References

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  1. ^ "Heinrich Hertz", The Electrician, July 20, 1894, page 333. Hertz's paper was titled "On the Propagation of Electric Waves along Wires".
  2. ^ "Multiplex Telephony and Telegraphy by Means of Electric Waves Guided by Wires" by George O. Squier, Proceedings of the American Institute of American Engineers, May, 1911, pages 857-862. Squier assigned ownership of his U.S. patents to "the American People". He later unsuccessfully tried to claim that this had not exempted commercial concerns from paying royalties on his patents.
  3. ^ a b "Telephony over Power Lines (Early History)" by Mischa Schwartz, "Presented IEEE History Conference, Newark, New Jersey, August 2007 and annotated since". (ethw.org)
  4. ^ "Interplant Telephonic Communications Established Over High-Tension Lines", Electrical World, July 17, 1920, page 141.
  5. ^ "Giving the Public a Light-Socket Broadcasting Service" by William Harris, Jr., Radio Broadcast, October 1923, pages 465-470.
  6. ^ "Dr. George Abraham, Ph.D" (collegebroadcasters.us)
  7. ^ "David W. Borst" (collegebroadcasters.us)
  8. ^ The Gas Pipe Networks: A History of College Radio 1936-1946 by Louis M. Bloch, Jr., 1980, pages 11-13.
  9. ^ Bloch (1980) pages 102-103.
  10. ^ "Radiator-Pipe Broadcasters" by Erik Barnouw, The Saturday Evening Post, May 24, 1941, pages 36, 79-80.
  11. ^ Bloch (1980) page 45.
  12. ^ "Low Power Radio" (FCC.gov)
  13. ^ "Welcome to BullsRadio.org". Bullsradio.org. Archived from the original on 2009-09-28. Retrieved 2009-10-25.
  14. ^ "Kamp Student Radio". kamp.arizona.edu. Archived from the original on 2009-10-02. Retrieved 2009-10-16.
  15. ^ "KANM 99.9 FM Cable - 1600 AM". 5 December 1998. Archived from the original on 5 December 1998.
  16. ^ a b "Kasc - arizona state's original alternative". Archived from the original on 2010-06-19.
  17. ^ "KDUP – Bluff Radio". kdup.up.edu.
  18. ^ http://www.kjack.org/ http://www.kjackradio.com/
  19. ^ "KLBC 1610AM - "Truly Underground Radio"". www.klbc.org.
  20. ^ KMSC Dragon Radio: About.
  21. ^ "K-ROCKS Radio One - We Don't Do Cute at KROCKS!". krocksradioone.com. Archived from the original on 2012-06-20. Retrieved 2012-06-15.
  22. ^ "Kutztown University Radio Services". Archived from the original on 2009-09-26. Retrieved 2009-10-16.
  23. ^ https://web.archive.org/web/20111121074604/http://www.kute.utah.edu/ http://kuteradio.org/
  24. ^ RadioSNHU. "RadioSNHU". radio.snhu.edu.
  25. ^ "The U". umslradio.com.
  26. ^ "Archived copy". listentowalt.com. Archived from the original on 18 May 2014. Retrieved 12 January 2022.{{cite web}}: CS1 maint: archived copy as title (link)
  27. ^ "WPR – UNR Student-Run Radio Station".
  28. ^ "WPPJ - Point Park University". www.pointpark.edu.
  29. ^ https://web.archive.org/web/20170922094625/http://wpmd.org/ https://web.archive.org/web/20161211110723/http://www.wpmdonthenet.com/about/
  30. ^ "WSIN - SCSU Independent Radio". radio.southernct.edu.
  31. ^ "Home -". Archived from the original on 2014-05-03. Retrieved 2014-05-03.
  32. ^ "The great 58 // Show Me Mizzou // University of Missouri". showme.missouri.edu. Retrieved 2022-06-01.
  33. ^ "16/KCIZ :: KCIZ-AM 1650, Mora, Minnesota". Archived from the original on 2008-09-29. Retrieved 2008-09-29.
  34. ^ Peek, Jerry. "KRWG Radio, Las Cruces, NM -- History and FM's 10th Anniversary". jpeek.com.
  35. ^ "Pomona College's KSPC-FM: real pro station". Progress Bulletin. 17 December 1977. p. 28. Retrieved 10 August 2023 – via Newspapers.com.
  36. ^ https://kxsuseattle.wordpress.com/ https://web.archive.org/web/20160323002125/http://www.ksubseattle.org/ http://www.seattlespectator.com/2015/10/21/seattle-u-student-radio-entering-a-new-era/ https://www.seattleu.edu/alumni/su-voice-alumni-blog/from-ksub-to-kxsu---big-changes-for-seattle-university-student-radio.html Archived 2017-11-15 at the Wayback Machine http://www.seattleu.edu/ksub/default.aspx?id=42100 Archived 2010-06-01 at the Wayback Machine
  37. ^ "Category:WCBN - Ann Arbor - ArborWiki". 2011-01-07. Retrieved 2011-09-27.
  38. ^ "CBN History Part I: Residence Hall Studios". Retrieved 2011-09-27.
  39. ^ "WKDT "Voice of the Long Gray Line" Now Online". Radio World. 2019-04-29. Retrieved 2022-06-01.
  40. ^ "Station History | WKDU 91.7 Philadelphia". Archived from the original on 2008-10-04. Retrieved 2008-08-07.
  41. ^ Sharma, Rekha (November 18, 1999). "WKSR uses Internet broadcasting to pass competition". The Daily Kent Stater. Kent, Ohio. p. 6. Archived from the original on May 21, 2022. Retrieved May 20, 2022.
  42. ^ Peris, Kenny (September 12, 2005). "Black squirrels take over the radio". The Daily Kent Stater. Kent, Ohio. p. 6. Archived from the original on May 21, 2022. Retrieved May 20, 2022.
  43. ^ Walsh, Glenn A. "History of Radio Station WLCR-AM: Carrier Current, Lewisburg/White Sulphur Springs, West Virginia and The Radio Group". johnbrashear.tripod.com. Retrieved 2022-06-01.
  44. ^ Grisez, Abby (March 29, 2018). "Queer Eye Creator On Time At Ohio University". WOUB Public Media. Retrieved 2022-06-01.
  45. ^ "The Rock Lobster". ACRN. April 4, 1971. Archived from the original on July 1, 2012. Retrieved October 6, 2011.
  46. ^ "WMUC - The University of Maryland, College Park". 9 October 2002. Archived from the original on 9 October 2002.
  47. ^ "Join a Student Organization - Penn State Student Affairs". www.clubs.psu.edu.
  48. ^ WRCR alumni site
  49. ^ O'Neil-White, Thomas (May 14, 2019). "Protests over the elimination of student-owned services corporation". news.wbfo.org. Archived from the original on April 13, 2021. Retrieved 2021-04-13.
  50. ^ "Carrier Current Radio Used in Housing Project" (PDF). Broadcast Management Engineering. Vol. 9, no. 11. November 1973. p. 55. Retrieved June 1, 2022 – via World Radio History.
  51. ^ "88.1 - WRGP Radiate FM& - 95.3". www.wrgp.org.
  52. ^ "W.U.S.B." (PDF). The Statesman. October 3, 1963. p. 3.
  53. ^ This Is College Radio (1956) - WYBC Yale Radio & the Ivy (Radio) Network on YouTube

Further reading

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