FM means "Frequency Modulation," indicating that the program matter causes the carrier *frequency* to change in proportion to the program level. The FM band in the USA runs from 88 MHz to 108 MHz (88.1 to 107.9), at 200 kHz intervals.
On December 26, 1933, Edwin Howard Armstrong was issued five basic patents on his FM system. (There is published record of Westinghouse and KDKA building experimental FM operations even before Armstrong's 1935 demos.) At the same time, it is important to remember that many stations in the "VHF" band were still amplitude modulated. Actual "official" FM operations began in 1940/41.
Major Armstrong (U.S. Signal Corps, WWI) conducted the first regular transmissions of the FM techniques used today beginning in 1935 on a frequency of 42.1 MHz from a transmitter loaned him by RCA atop the Empire State Building in New York. On April 10, 1938, Armstrong began the experimental station W2XMN on 43.7 MHz. at 600 Watts. "Full Power of 35,000 Watts and regular programming was reportly begun on July 18, 1939. The station lasted until 1954.
Several more stations began regular "program service" in 1940 as GE and other manufacturers started making quantities of FM receivers. All were still considered "experimental" and were operated without commercial content.
The FCC permitted regular "commercial operation" of FM stations in 1941, and the first commercial FM station, W47NV (now WSM-FM) in Nashville, signed on during New Year's Day of 1941.
The first Non-Commercial FM station was KALW, San Francisco. Owned by the SF Unified School District, this station was licensed in March of 1941, and apparently signed on officially sometime between then and September. (This station was equipped with a converted RCA unit, given to the District after the 1939-40 Golden Gate International Exposition.
Armstrong also operated a subcarrier on that transmitter and demonstrated transmission of facsimile, to show that newspapers might also be delivered by radio broadcast stations. His facsimile demonstrations were carried on later by a number of FM stations, most notably those of the Cox broadcast and newspaper group, including WIOD-FM in Miami.
This is an interesting story, worthy of longer attention. The early experiments with FM broadcasting, by Armstrong and others, was on a number of different frequencies. However, in the 1930s, when the FCC decided to allow FM broadcasting to begin, the band from 42-50 MHz was originally assigned for use.
Those who have read books on broadcast history will recall that David Sarnoff was now actively working against Major Armstrong and his FM developments. More than just envy and personal differences were involved, as Sarnoff wanted to start "rolling out" television, where he saw more income potential than FM. Sarnoff went to the FCC and demanded the same frequencies as FM was using. This accomplished several things. One, it made existing FM radios useless. Two, as television moved down to 48 MHz, it forced FM stations to move way up the dial, to 88-108 MHz, which cost struggling stations so much money that many just gave up. And three, it gave Sarnoff a real jolt to frustrate Armstrong, who finally committed suicide.
Of course, the US band of 88-108 MHz (with the lower 4 MHz reserved for non-commercial educational stations) is not the standard throughout the world. For example, in Eastern Europe stations were slotted in the 65-74 MHz range, both to make the radios useless for receiving western stations (during the cold war), and to provide some collateral "jamming" to the television in Western Europe. Over in Japan, 76-90 MHz is used for FM broadcast. In the UK, "standard" radios could pick up the police calls on "VHF" for many years, much like it used to on AM in the US, decades ago when the police used frequencies at the high end of the AM band.
Currently the highest permitted power in the US is 100,000 watts. However, there are many stations grandfathered with higher power levels. The highest, WBCT, Grand Rapids, MI runs 320 kW at 780 ft. This Clear Channel (formerly owned by Fetzer Broadcasting) station had a CP at one time for 550 kW; and ran as much as 470 kW Horizontal at 800 ft.
WMC-FM is licensed for 300 kW in Memphis
WSRW-FM is licensed for 265 kW at Grand Rapids, MI
In Canada, CITI FM ran 360 kW until it dropped to 140 kW.
In the 1950s, RCA was said to have built three stations for operation at 500 kW. One (WBCT) is still running well into "superpower" ... while the others are closer to 100 kW today.
It has been reported that one station in Northern Italy, broadcasting into Zurich, is running an ERP of 2,000,000 watts!
| Site | Location of Site | Tower height AGL | Tower Height AMSL | Radiation Center AMSL | Radiation Center HAAT |
| KLTN | Devers, TX | 607 m (1992 ft) | 622.5 m (2042 ft) | 609 m (1998 ft) | 595 m (1952 ft) |
| Senior Road | Houston, TX | 601 m (1971 ft) | 624.5 m (2049 ft) | 605 m (1984 ft) | 585 m (1919 ft) |
| KLDE** | Lake Jackson, TX | 610 m (2000 ft) | 615 m (2018 ft) | 604 m (1981 ft) | 601 m (1971 ft) |
| KVLY-TV | Fargo, ND | 628.8 m (2063 ft) | . | 913 m (2995.4 ft) | 610 m (2000 ft) |
| KXJB-TV | Valley City, ND | 628 m (2060 ft)* | . | 925 m (2802 ft)* | 600 m (1817 ft)* |
| KKUA | Wailuku, HI | . | . | 3043 m (9983.3 ft) | 1685 m (5528 ft) |
| KKOB | Albuquerque, NM | . | . | 3274 m (10741.5 ft) | 1265 m (4150 ft) |
| KWUT | Elsinore, UT | 3600 m (11,811 ft) |
993 m (325 ft) |
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Yes. While it used to be unusual, there are now many directional FM stations.
Actually, there are more unofficial directional stations than non-directional, since the tower is really a parasitic radiator. Some stations have actually taken advantage of this effect to produce a "power boost" toward their desired market.
The FCC authorized regular stereo FM to start on 6/1/61. WEFM Chicago and WGFM Schenectady both started on that date.
This unique system, where one channel was on AM and the other on FM was popular for a while. Some receivers (Fisher) still exist.
The first LPFM station went on the air June 21, 2001 in Alexandria, LA. KCJM-LP was licensed for operation on 107.9 MHz. The stated goal of this station was to teach young people, ages 12-24, the business of broadcasting.