Carrier current

Carrier current is a method of low power AM broadcasting that does not require a broadcast license in the United States, but is allowed on the campus of any school, so long as the normal FCC Part 15 Rules are adhered to when measured at the edge of the campus. Most college radio stations started out this way, using the electrical system of a building to distribute an AM radio signal. This is one method used for college and high school radio, particularly if the signal is only intended to be picked up in a small area. While the technology is still used by a number of student-run stations today, the popularity declined beginning in the 1980s, as popular music radio formats quickly migrated to the FM band. The popularity of streaming audio over the Internet has hastened this decline.

Carrier current stations generally only have an effective radiated power of a few watts. These signals cannot pass through transformers, however, and are prone to the electromagnetic interference from alternating current. Transmitters that use carrier current are very simple, making them an effective option for students interested in radio. Transmissions can be of good quality, although there is a low frequency background hum (60 hertz in North American installations) associated with carrier current, due to the alternating current. Not all listeners notice this hum, nor is it reproduced well by all receivers.

Carrier current is available for any user, and is not restricted to campus operations. There are many examples of community radio stations being operated in the United States using carrier current AM broadcasting. Signals "may" pass a transformer if the utility company has bypass lines installed (typically when non-conflicting carrier current-based data systems of their own are in operation). Signals may also be impressed onto the neutral leg of the 3-phase power system, a practice known as "neutral loading", in an effort both to reduce (sometimes eliminate) 60 Hz hum, and to extend effective transmission line distance. It has been successful in both ways in community and campus installations.

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.

Because of their simple design and the fact that the transmitter doesn't need an external antenna, carrier current listening devices have found some use in the world of espionage.

tudent-run carrier current or cable cast stations

As with most other student-run stations, these stations often operate on sporadic schedules. Most of these stations are also supplemented by other broadcasting methods, such as LPFM, closed circuit, and streaming audio. Many carrier current stations have been, and continue to be, replaced by these technologies as well. Though legal, these stations are not licensed by the FCC and their call letters are entirely self-styled.

Existing stations

* [http://www.theblaze1260.com/ KASR-1260] Arizona State University
*KRFH at Humboldt State University
* [http://www.kute.org/ KUTE-1620] University of Utah
*KVCM at Los Angeles Valley College
* [http://waug.augustana.edu/ WAUG 97.9 FM cable cast] at Augustana College
* [http://werw.syr.edu/ WERW 1570 AM] Syracuse University
*WEXP at La Salle University
*WFVS 530 AM and recently LPFM at 100.5 at Fort Valley State in Fort Valley, GA (fiber-optic linked carrier current system)
* [http://www.myspace.com/wmax540 WMAX 540] at Hesser College, Manchester NH
* [http://www.pointpark.edu/default.aspx?id=350 WPPJ-670] Point Park College
*WVYC 640 AM at York College of Pennsylvania, sister station to FCC licensed WVYC FM 99.7 also on the Internet.

Former stations

*K.C. AM at Colby College, now WMHB
*KAL at University of California, Berkeley - now KALX
*KCC at Chabot College, Hayward, CA - now KCRH 89.9
*KCWS-AM at Central Washington State College - now KCWU-FM
*KDVS, originally KCD at University of California, Davis
*KFRH at Washington University in St. Louis - now KWUR-FM
*KOWL at Rice University - now KTRU-FM
* [http://www.geocities.com/wdbs560/ WDBS 560-AM] at Duke University - now WXDU-FM 88.7
*WFAL 1610AM at Bowling Green State University
*WHEN at Western Illinois University - now WIUS-FM
*WJJX 650AM at the University of Michigan, sister station to WCBN-FM 89.3
*WJPZ at Syracuse University, now 89.1 FM
*WKC at Knox College - now WVKC-FM
* WKDU-FM 91.7, the student-run radio station of Drexel University formally WMAX (1958) [http://www.wkdu.org/node/5]
*WKDT 89.3 FM, the cadet radio station, United States Military Academy, West Point, NY
*WLKR AM Lake Superior State University, Sault Ste. Marie, MI - Now WLSO 90.1 FM "The Sounds of Lake State"
*WNYU on 800 AM in New York University's dorms at its lower Manhattan campus.
* [http://www.gregssandbox.com/wocr/ WOCR-650] A "pirate" carrier current station in Ocean City, MD in 1973
*WOLF at North Carolina State University in Raleigh, North Carolina - now WKNC
*WPSM at Penn State's Mckeesport Campus (aka Penn State Allegheny) - now an internet station WMKP [http://www.clubs.psu.edu/mk/wmkp/]
*WQAD/WFQR/WIN/WIUS at Indiana University - now WIUX-LP
*WRAF on 590 AM at Binghamton University - now WHRW
*WRLC-AM on 1110 and 1150 AM at Rutgers University, now WVPH-FM
*WRCK at Slippery Rock University - now WRSK-FM
*WRCT on 900 AM at Carnegie Mellon University - now WRCT-FM
*WRUR-AM 1090 at University of Rochester in Rochester, New York - now WRUR-FM see also Campus Radio
*WSOE on 1200 AM at the Milwaukee School of Engineering in Milwaukee, Wisconsin - now WMSE on 91.7 FM see also Campus Radio
* [http://www.wrgp.org/ WUFI-540AM] at Florida International University now WRGP 88.1 & 95.3 FM
*WVAU on 610 AM at The American University (station is still present, but they no longer broadcast carrier current)
*WVBU on 640 AM at Bucknell University later licensed to 90.5 MHz FM, carrier current turned off several years later
*WXOU 88.3 FM at Oakland University in Rochester Hills, Michigan (Licensed to Auburn Hills, Michigan)
* [http://www.wxpn.org/wxpn/ WXPN] WXPN and WQHS-730] at the University of Pennsylvania

ee also

*Power line communication