Time-sharing arrangements among AM stations date back to the earliest days of broadcast regulation in the late 1920s. Especially after a massive reallocation of stations on November 11, 1928, smaller stations were forced to "double-up" by sharing time.
As directional antennas and other techniques were developed, more and more stations were able to get "their own space", so to speak. Most time-sharing arrangements are no more. However, at least two remain on the AM dial, a third one ended only in 2002, and a fourth existed in Chicago until 1997.
WIBW and KKSU in northeastern Kansas
The time-sharing arrangement between a commercial broadcaster and Kansas State University ended in November 2002. Until the 27th of the month, commercial broadcaster WIBW in Topeka shared its time, but not its transmitter, with KKSU.
KKSU, formerly KSAC, began sharing time with WIBW on November 30, 1929. More details about the history of KKSU's time-sharing arrangements are in the KKSU history at this site.
In its final incarnation, KKSU broadcast weekdays from 12:30 to 5:30 pm, with WIBW on the air at all other times. This was a slight modification of a time-sharing schedule that had been in effect since October 2, 1961.
Topeka was home to another time-sharing agreement between WREN and the University of Kansas' KFKU. When WREN left the air in 1987, the one hour daily broadcasts of KFKU also ceased because KFKU did not have a separate transmitter. KFKU programming did not resume when WREN returned to the air in 1993. There is conflicting information on whether KFKU surrendered its license after 1987 or whether the FCC deleted the license in 1997. In the meantime, WREN had moved its license from Topeka to Kansas City, Kansas, and its transmitter from Grantville, Kansas to Kansas City, Missouri.
Listen to these samples of the hand-offs between KKSU and WIBW
Time-sharing stations in Chicago
1240 kHz (WCRW, WEDC, WSBC)
Until July 1996, 1240 kHz was the home of the last three-way time-sharing arrangement in the United States. WCRW, WEDC, and WSBC, all broadcasters specializing in ethnic and specialty programming, shared this frequency.
In May 1996, WSBC bought out WCRW, for a price of $762,500, as reported by the M Street Journal (July 17, 1996). In July, WSBC took over WCRW's time in addition to its own. WSBC once owned WXRT(FM) and WSCR(AM) in Chicago, which were subsequently sold to Westinghouse Broadcasting.
On June 13, 1997 at midnight, WSBC assumed control of WEDC's time as well, putting an end to the last of the original time-sharing arrangements in the United States.
WSBC and WEDC used separate transmitter sites, located within a mile of each other on the northwest side of Chicago. With the 1997 merger, WSBC also began using WEDC's transmitter on a full-time basis. The WSBC-WEDC time-sharing schedule, confirmed by listening to the stations, was:
|12:00 am - 6:00 am||WEDC|
|6:00 am - 8:30 am||WSBC|
|8:30 am - 10:00 am||WEDC|
|10:00 am - 3:30 pm||WSBC|
|3:30 pm - 5:00 pm||WEDC|
|5:00 pm - 7:00 pm||WSBC|
|7:00 pm - 8:00 pm||WEDC|
|8:00 pm - 10:00 pm||WSBC|
|10:00 pm - 11:00 pm||WEDC|
|11:00 pm - 12:00 am||WSBC|
You can see that WEDC used the frequency 11 hours a day (with six of those hours in the overnight period) while WSBC had 13 hours a day of air time.
1450 kHz (WCEV and WRLL, formerly WVON)
Licensed to Cicero, a suburb next to the southwest side of Chicago, these stations share a transmitter in the city of Chicago proper. The daytime signal covers most of Chicago, though, on some car radios, there is interference northwest of O'Hare airport caused by proximity to the 50,000-watt transmitters of WMAQ, WGN, and WBBM. At night, along the shore of Lake Michigan, the signal begins to encounter the typical class C "graveyard channel" co-channel interference at Belmont Avenue (3200 North). Similar results were obtained inland at Ashland Avenue (1600 West). Mark definitely couldn't hear it well at night at his Chicago location in 1997 and 1998 in Edgewater (5700 North).
Still, Mark managed to hear the sign-ons and sign-offs for each station when he lived in Chicago. The schedule is:
|12:00 am - 1:00 pm||WRLL||12:00 am - 5:00 am||WRLL|
|1:00 pm - 10:00 pm||WCEV||5:00 am - 10:00 pm||WCEV|
|10:00 pm - 12:00 am||WRLL||10:00 pm - 12:00 am||WRLL|
|(On Saturdays, WCEV hands off to WRLL at 8:30 pm.)|
This time-sharing arrangement was a relatively recent development. An earlier station named WVON at 1450 kHz was vacated in 1975 when it purchased a more powerful station at 1390 kHz (now WGCI). The Federal Communications Commission asked classical music broadcaster WFMT to program the frequency for a few years while it evaluated applicants for the vacated frequency. In 1978, the signal was granted to two applicants, WXOL and WCEV. WXOL changed its call letters to WVON in 1984, according to FCC records.
In 2006, WVON reached an agreement with Clear Channel Communications to lease Clear Channel's expanded-band station, WRLL. The move would allow WVON to broadcast 24 hours a day. The lease also includes an option for WVON's owner to buy the channel. WVON moved its programming to 1690 kHz and expanded its schedule to 24 hours a day on September 18, 2006. The WRLL call letters moved to 1450 kHz, still sharing time with WCEV. (Thanks to Scott Fybush of fybush.com's Northeast Radio Watch for additional information and insights on the origins of this time-sharing arrangement.)
On January 20, 2020, WCEV discontinued operations and filed for authority to remain silent. It did not return to the air before the one-year deadline under section 312(g) of the Communications Act. WRLL filed to terminate the share-time agreement and requested full-time authority for 1450 kHz on March 3, 2021.
Audio Sample and links
Time-sharing stations in Decorah, Iowa
Another time-sharing arrangement still exists between a commercial station and a non-commercial station in Decorah, Iowa, near the Minnesota border. Commercial station KDEC and Luther College station KWLC share time at 1240 kHz. FCC records indicate that the stations broadcast from separate transmitting sites. The KWLC web site gives the station's hours as 10 pm to 1 am on weekdays and 7:00 am to 1:00 am on weekends. KDEC's web site doesn't provide a schedule of the station's operating hours. Presumably it broadcasts when KWLC isn't on the air, but it appears likely that neither station broadcasts in the overnight hours.
FCC records indicate that KDEC had at one time tried to move to a different frequency, thereby eliminating the need to share time. An application from 1981 contains this notation:
CP CHG FREQ 1200KHZ, INCR NIGHTPOWR 1KW, CHG TL3.5 MI SW OF DECORAH ON US 52, 43 15 06 91 50 24 CHG FROM NON DA TO DA-2, GO FROM SHARE TIME OPR. TO SEPARATE FULLTIME OPR.
In English, that means the station wanted to move to 1200 kHz, increase nighttime power to 1,000 watts with a directional antenna using separate patterns day and night, and relocate its transmitting site. The request was approved by the FCC in 1983, giving KDEC one year to construct the new facility. However, a licence to cover was never applied for, and two requests in 1984 to extend the time allotted to build the proposed facility were denied by the FCC. In 1991, KDEC requested a power decrease to 580 watts and a change in transmitting coordinates, indicating that the station was moving its transmitter site. The proposal was considered a "minor change" not requiring an environmental study, unlike the 1981 proposal. It was approved July 11, 1991.
KWLC still broadcasts with 1,000 watts, indicating that it has not moved in the last couple of decades, at least.
Thanks to Joel Hermann, who posted about this arrangement in the rec.radio.broadcasting Usenet discussion group (newsgroup).
Other Time-Sharing stations
There are also examples of FM stations sharing time.
In the Minneapolis suburb of St. Louis Park, the The St. Louis Park school district agreed to share their 10-watt FM Station, KDXL, on 106.5 MHz with the University of Minnesota's student-run radio station, KUOM (AM). The new station, KUOM-FM, received its construction permit in 2002 and a licence to cover in 2003. Under the sharing agreement, KDXL operated when school was in session. During evenings, weekends, and the summer months, KUOM-FM broadcast. The time-sharing agreement ended in 2018 when the School District surrendered the KDXL licence, allowing KUOM-FM full use of the 106.5 slot.
There are also new time-sharing agreements among low-power FM stations, particularly in larger markets where space on the FM dial is already limited. For example, in the San Francisco/Oakland area, there are three frequencies where LPFM stations are sharing time.
96.1 MHz: KEXU-LP Oakand, KJTZ-LP Alameda, and KJTZ-LP Alameda.
96.9 MHz: KQEA-LP San Francisco - Sunset, KQEB-LP San Francisco, and KGPC-LP Oakland
102.5 MHz: KXSF-LP San Francisco and KSFP-LP San Francisco (under construction)