FM Basics

FM transmitters modulate a carrier wave signal's frequency rather than its amplitude. That is, the power output remains the same at all times, but the carrier wave frequency changes in relation to the information (music or talk programs, e.g.) transmitted. Electronic static (most of which is amplitude modulated) may flow with but cannot attach to FM waves, which allows the desired FM signal information to be separated from most interference by special circuits in the receiver.

Because U.S. FM channels are each 200 kilohertz wide (allowing a wide frequency swing), a high-quality sound image is transmitted (up to 15,000 cycles per second-almost three times the frequency response of AM signals and close to the 20,000-cycle limit of human hearing), usually in multiplexed stereo. The cost for this sound quality is paid for in spectrum-each FM station takes up 20 times the spectrum of a single AM station, although only a portion is used for actual signal transmission, with the remainder serving to protect signals of adjacent stations. FM radio in the United States is allocated to the very high frequencies (VHF), occupying 100 channels of 200 kilohertz each between 88 and 108 megahertz. Each FM channel accommodates hundreds of stations-there are more than 7,000 on the air at the beginning of the 21st century.

VHF transmissions follow line-of-sight paths from antenna to receiver, and thus FM transmitters (or television stations, which use neighboring frequencies) are limited in their coverage to usually not more than 40 to 60 miles, depending on terrain and antenna height. That limitation is balanced by the lack of the medium wave interference that AM radio has, which is caused by signals arriving from ground waves or sky waves at slightly different times because of the distances covered.

Experimental Development (to 1940)

No one person "invented" FM radio-indeed, the man most credited with developing the system, Edwin Howard Armstrong, readily conceded that point. The first patents concerning an FM transmission system were granted to Cornelius Ehret of Philadelphia in 1905, probably the first such patents in the world. Scattered mentions of FM in subsequent years focused on its negative aspects, suggesting that, based on what was then known, FM would not be a useful broadcast medium. Still, technical work continued, and more than two dozen patents had been granted to various inventors and companies by 1928. Much of the impetus behind research into FM work was the search for a solution to the frustrating interference problem with AM radio. By the late 1920s, it was clear that simply using more AM transmitter power would not overcome static, which made AM unlistenable in electrical storms. Something new was needed.\

From 1928 to 1933, Edwin Armstrong, a wealthy radio inventor then on Columbia University's physics faculty, focused on trying to utilize FM in a viable broadcast transmission system. Rather than working with narrow bands as had others before him, Armstrong's key breakthrough was to use far wider channels, eventually 20 times wider than those used by AM. The frequency could then modulate over about 150 kilohertz (though it normally used far less), leaving 25-kilohertz sidebands to prevent interference with adjacent channels. This allowed for greatly improved frequency response, or sound quality. Armstrong incorporated various circuits to allow precise tuning of the wide channels while at the same time eliminating most static and interference. Armstrong applied for the first of his four basic FM patents in 1930 and for the last in 1933; all four were granted late in 1933.

From 1934 to 1941, Armstrong further developed and demonstrated FM, working toward Federal Communications Commission (FCC) approval of a commercial system. After a number of long-distance tests (successfully sending signals up to 70 miles with only 2,000 watts of power) in cooperation with the Radio Corporation of America (RCA), Armstrong announced his system to the press early in 1935. A more formal demonstration to a meeting of the Institute of Radio Engineers later that year (and the published paper that resulted) marked the beginning of active FM innovation.

Resistance to the FM idea began to develop at about this time, usually growing out of the competing interests of two other broadcast services. Owners of AM stations, including the major networks, were concerned about the new technology that might totally replace their existing system. And companies already investing heavily in television research, especially RCA, thought that the new video service should receive priority in allocations and industry investment. FM was seen by some as merely a secondary audio service, albeit a far better one technically.

In July 1936 Armstrong obtained permission from the FCC to construct the world's first full-scale FM station in Alpine, New Jersey, across the Hudson River from New York City. After a technical hearing, the FCC provided initial allocations for FM and television (among other services), granting the fledgling FM technology's backers the right to experiment on 13 channels scattered across three widely separated parts of the spectrum-26, 43, and 117 megahertz. Early in 1939 the allocation was expanded to 75 channels located more conveniently between 41 and 44 megahertz. In the meantime, Armstrong's experimental station-the world's first FM transmitter-had gone on the air as W2XMN with low-power tests in April 1938.

Developing further experimentation but also looking toward commercial FM operations, the New England-based Yankee Network began to build two large transmitters in 1938-39. General Electric built two low-power FM transmitters at the same time, and the National Broadcasting Company's (NBC) experimental station began operating in January 1940. The first FM station west of the Alleghenies began transmission tests in Milwaukee just a few days later. Transmitters for most of these operations came from Radio Engineering Laboratories. Receivers were first manufactured by General Electric in 1939, with other companies joining in the next year; however, most FM sets cost a good deal more than their AM counterparts.

Early Operations (1940-45)

The FCC became the arena for a 1940 battle over whether or not to authorize commercial FM service, and if so, on how many channels and with what relationship to developing television. In March 1940, more than a week of hearings were held to air the industry's conflicting views over the merits of FM and television. On 20 May 1940, the commission released its decision allowing the inception of commercial FM operation as of 1 January 1941; the decision allocated 40 channels on the VHF band (42-50 megahertz), reserving the lowest five channels for noncommercial applicants. Final technical rules were issued a month later. The first 15 commercial station construction permits were issued on 31 October 1940.

As the new year dawned, 18 commercial and 2 educational stations aired (compared to more than 800 AM stations at the time). The first commercial license was granted to W47NV, affiliated with AM station WSM in Nashville. The first West Coast station, a Don Lee network outlet, went on the air in September 1941. FM outlets briefly used unique call signs that combined the letters used with AM stations with numbers indicating the channel used (e.g., W55M in Milwaukee broadcast on 45.5 megahertz). This system was replaced with normal four-letter call signs in mid-1943.

By the end of 1941, and after the United States had entered World War II, the FCC reported 67 commercial station authorizations, with another 43 applications pending. About 30 of the former were actually on the air. Wartime priorities forced the end of further license grants and limited construction material availability after March 1942. By the end of October 1942, 37 stations were in operation, plus an additional 8 outlets still devoted to experiments. But construction materials and replacement parts were increasingly difficult to find, and some owners turned back their authorizations or withdrew their applications pending the end of the war.

The first attempt at an FM network, the American network, never made it on the air, largely because of difficulties in constructing the needed affiliate stations in sufficient markets. Programs offered on FM were of two types-duplicated AM station signals (the most common type) or recorded music. Because of the duplicated content of existing stations, FM stations had little appeal for advertisers. Another problem was FM audiences. There were some 15,000 FM sets in use at the beginning of 1941 and perhaps 400,000 by the time manufacturing was stopped early in 1942, compared to 30 million AM-equipped households. Most observers expected FM to become an important part of the industry after the war.

Frequency Shift and Decline (1945-57)

The next dozen years-from 1945 through 1957-were both exciting and frustrating as the FM service struggled to become established and successful amidst a broadcasting industry increasingly infatuated with television and still investing considerable sums into the expansion of AM. Initial excitement over FM's potential gave way to a slow decline.

Toward the end of the war, potential operators were already concerned that FM's allocation of 40 channels was not sufficient for expected postwar expansion. To further complicate matters, wartime spectrum and related research suggested that the FM allocation of 42-50 megahertz might be subject to cycles of severe sun spot interference. Concerns about television expansion led to demands by some members of the industry for FM's spectrum space to be reallocated to television.

Extensive FCC hearings in mid-1944 aired some of the technical concerns about the FM band, though wartime security limited what could be discussed. Armstrong and his backers argued to retain ( or, better yet, to expand) the existing allocation, in part because stations could easily network by picking up each other's signals and passing them on-something that would be impossible were FM to be moved higher in the spectrum (moving lower was out of the question because of existing services). In January 1945 the FCC proposed moving FM to the 84-102 megahertz band to avoid the expected atmospheric interference and to gain more channels, for a total of 90. Subsequent proceedings continued the industry split over what to do and how. Finally, in June 1945, the FCC made its decision, shifting FM "upstairs" to the 88-108 megahertz band with a total of 100 channels that the service occupies today. Continuing the precedent established in 1941, educational users were assigned to channels reserved for them at 88-92 megahertz. The former FM band would be turned over to television and other services after a three-year transition period.

At first it seemed the shift would only disadvantage those stations actually on the air (46 at the time) and those people with FM sets that could not also receive AM signals (perhaps 30,000 old-band FM-only sets in consumer hands). Generally FM's outlook was good. The FCC issued the first postwar grants for new stations in October 1945, and more applications were piling up. Through 1946 there were always at least 200 applications pending, and although the number of stations actually on the air grew fairly slowly, the number of authorized FM stations exceeded 1,000 by 1948-more than all the AM and FM stations on the air just three years earlier. Most applications were coming in from AM stations hedging their bets on the future. Several government agencies issued optimistic publications encouraging still more FM applicants. Two specialized FM trade magazines began to publish. A number of potential FM networks were in the planning stages, and the first, called the Continental network, began operations with four stations early in 1947.

But all was not well. FM's frequency shift was more damaging in the short term than it had seemed. When stations began to transmit on FM's new frequencies, there were few receivers available to pick up the signals. Manufacturers were trying to meet pent-up wartime demand for new AM sets and had little capacity to devote to FM's needs. Thus FM suffered from the lack of a good-sized audience that might appeal to advertisers. Only token numbers of receivers were available until 1950, and by then demand for television sets was threatening capacity devoted to radio. FM's lack of separate programming (after considerable industry argument both ways, the FCC had allowed co-owned AM and FM stations to simulcast or carry the same material) offered little incentive for consumers to invest in one of the rare and expensive FM receivers. A cheap AM set could tune popular local and network radio programs just as well. FM's better sound quality was not enough of a draw. What independent programming did exist was largely classical music and arts material of interest to a relatively small elite. Advertisers saw no reason to invest in FM, especially when FM time was usually given away with AM advertising purchases. Indeed, AM was thriving-more than doubling the number of stations on the air from 1945 to 1950. And the growing concentration on television by broadcasters, advertisers, and the public made FM seem unnecessary.

As these factors combined and intensified, the results soon became apparent. The number of FM new station applications began to drop off, and then overall FM authorizations declined. By 1948 FM stations already on the air, among them some pioneering operations, began to shut down, returning their licenses to the FCC. FM outlets could not be given away, much less sold. The number of stations on the air declined each year. Faced with the seeming failure of his primary invention, Armstrong took his own life in 1954; with the loss of his financial backing, the Continental network had to close down as well.

Rebound(1958-70)

Then, and at first very slowly, FM began to turn around. Reports in several trade magazines late in 1957 picked up the fact that the number of FCC authorizations for FM stations had increased for the first time in nine years. Slowly the pace of new station construction picked up, first in major markets and then in suburban areas. Several factors underlay this dramatic shift.

First, AM had grown increasingly crowded-there were virtually no vacant channels available in the country's major markets. The number of AM stations had doubled from 1948 to 1958, and a bout 150 more were going on the air annually. However, an increasing proportion of the new outlets were limited to daytime operation in an FCC attempt to reduce nighttime interference. FM, with no need for daytime-only limitations, was now the only means of entering major markets. In addition, the major spurt of television expansion was over, and this eased up pressure on time, money, and personnel, which could now be applied to FM.

But aside from overcrowding in AM and television, FM itself had more to offer. In 1955 the FCC had approved the use of Subsidiary Communications Authorizations, which allowed stations to multiplex (to send more than one signal from their transmitter) such non-broadcast content as background music for retail outlets ("storecasting"). This provided a needed revenue boost. So did the growing number of listeners interested in good music. These "hi-fi" addicts doted on FM operations, and this interest was evident in the increasing availability and sale of FM receivers. A developing high-end audience led advertisers to begin to pay serious attention to the medium.

Another technical innovation gave FM a further boost: the inception of stereo broadcasting. Beginning as early as 1952, some stations, such as New York's WQXR, offered AM/FM stereo using two stations-AM for one channel of sound and an FM outlet for the other. Occasional network two-station stereo broadcasts began in 1958-the same year commercial stereophonic records first went on sale. By 1960, more than 100 stations were providing the two-station system of stereo. But such simulcasting wasted spectrum (two stations with the same content), and the uneven quality of AM and FM provided poor stereo signals. What was needed was a system to provide stereo signals from a single station, and FM's wide channel seemed to offer the means.

In 1959 the National Stereophonic Radio Committee began industry experiments with several competing multiplexed single-station systems. By October 1960 the committee had recommended that the FCC establish FM stereo technical standards combining parts of systems developed by General Electric and Zenith. The FCC issued the standards in April 1961, and the first FM stereo stations began providing service in June. By 1965, a quarter of all commercial stations were offering stereo; by 1970, 38 percent of FM stations had the capability. Though few saw the future clearly, stereo would be a key factor in FM's ultimate success over long-dominant AM stations.

FM's continued expansion led the FCC to establish three classes of FM station in mid-1962. Lower-powered Class A (up to 3,000 watts of power and a service radius of 15 miles) and B stations (up to 50,000 watts of power and a service radius up to 40 miles) would be granted in the crowded northeastern section of the country as well as in southern California. Higher-powered C stations (up to 100,000 watts of power providing a service radius of 65 miles) could be granted elsewhere. A five-year FCC freeze on most new AM station grants beginning in 1968 helped funnel still more industry expansion into FM as the FCC began to see AM and.FM as parts of an integrated radio service.

Of even greater importance to FM's continued growth was a series of landmark FCC decisions from 1964 to 1966 requiring separate programming on co-owned AM and FM stations in the largest markets (those with populations over 100,000). Long concerned about the effect of wasting spectrum space by allowing the same programs to run on both AM and FM, the FCC had been persuaded by industry leaders to allow the practice when FM was weak. Indeed, many FM broadcasters expressed great concern about losing their ability to carry popular AM programming. But FM's growth in numbers and economic strength prompted the move-which further accelerated creation of new FM stations. In just a few years the importance of the FCC decisions (which by the late 1960s had been extended to smaller markets) became apparent as FM audiences increased sharply-bringing, in turn, greater advertiser interest and expenditure to make FM economically viable for the first time in its history. By the early 1980s, when the AM-FM non-duplication requirement was eliminated in a deregulatory move, FM stations were dominant in large part because of their unique programming.

That FM had achieved its own identity was exemplified when one of the big-three networks, the American Broadcasting Companies (ABC), initiated a network of FM stations in 1968. Although relatively short-lived, as the industry increasingly began to think of FM as radio rather than something different, the recognition that such a network gave to FM radio was a tremendous boost in the advertising community. Another indicator was Philadelphia's WDVR, which within four months of first airing in 1963 was the number-one FM station in the city, competing for top spot with long-established AM outlets, an inconceivable development just a few years earlier. Five years later, the same station became the first FM outlet to bill more than $1 million in advertising time. The FM business as a whole reported positive operating income in 1968 for the first time (it happened for the second time in 1973, after which the industry as a whole remained profitable).

The key measure of FM's coming of age, of course, is actual audience use of the service. In 1958, for example, FM was available in about one-third of all homes in such major urban markets as Cleveland, Miami, Philadelphia, and Kansas City. By 1961 the receiver penetration figures for major cities were creeping up to about 40 percent, and national FM penetration was estimated at about to percent, showing how few FM listeners lived in smaller markets and rural areas, many of which still lacked FM stations. By the mid-196os, FM household penetration in major markets was hovering at the two-thirds mark, and national FM penetration stood at about half that level. Although stereo and car FM radios were initially expensive, increasing production dropped prices and helped to further expand FM availability. 

Dominance (The 1970s and Since)

After the many FM industry and policy changes of the 1960s, the 1970s saw FM becoming increasingly and rapidly important economically. Where FM attracted 25 percent of the national radio audience in 1972, just two years later survey data showed FM accounted for one-third of all national radio listening-although only 14 percent of all radio revenues. By 1979 FM achieved a long-sought goal when for the first time, total national FM listening surpassed that of AM stations. Every major market had at least four FM stations among the top 10 radio outlets. Indeed, FM would never lose that primacy, slowly expanding its role until by the turn of the century, FM listening accounted for nearly 80 percent of all radio listening.

Getting there had not been easy and had taken far longer than early proponents had expected. In part, FM's own success got in the way. After years of promoting FM's upper-scale (though small) audiences, often prejudicially dubbed eggheads and high-fidelity buffs, it was hard to shift gears and promote FM's large and growing audience as being tuned to simply "radio." (Indeed, the number of commercial FM classical music stations had actually declined by half since 1963, to only 30 by 1973.) At the same time, the number of educational FM stations expanded dramatically after 1965, greatly aided by the creation of National Public Radio and the appeal of its programs as well as by the availability of increased funding for station development and operation.

But with success came pressure to keep up. As news and talk formats increasingly defined AM (where the poorer sound quality did not matter), FM flowered with a full cornucopia of musical formats and styles. By the early 1970s, FM stations in the nation's largest markets were developing formats every bit as tight and narrow as those of their AM forebears. Each station and its advertisers were appealing to a specific segment of the once-mass radio audience in an attempt to build listener loyalty in a marketplace often defined by too many stations in most cities. By the late 1980s, FM's primary target market was that defined by its advertisers: listeners aged 26 to 34, followed by those 3 5 to 44 years of age. Only a relative handful of stations target teens, and fewer than 30 percent are interested in listeners aged 55 or older. As compared with its earlier days, FM has become positively mainstream.

FM's success is also seen in the usual marketplace measure-the price of FM stations being sold on the open market. Where top-market stations could literally not be given away in the early 1950s, by the late 1960s, the first million-dollar prices were being quoted. Three decades later, FM stand-alone stations in top markets sold for tens of millions of dollars, and some have sold for well over $100 million. On the other hand, many miss the old days of FM programs aimed at a small, elitist, sometimes cranky but usually appreciative audience. A 1999 FCC proposal to create scores of low-power FM outlets was intended to bring back some of that spirit, but was severely curtailed by Congress in 2000.

FM Outside the U.S.

FM or VHF radio developed more slowly outside of the United States. In Europe, for example, postwar radio reconstruction in most countries focused first on established medium wave and long wave services and then on television; few countries had economies strong enough to develop FM services at the same time as these other initiatives. And politics played a part, because Europe hoped in the meantime to find a European technical solution to its substantial problems of interference and static.

Given the total destruction of its broadcasting system, Germany had to start over and thus led Europe in beginning FM broadcasting. The first transmitters were on the air by 1949, and most of West Germany was covered with FM signals by 1951. Sale of FM receivers was brisk (some were exported to the United States), partly because television was not a competitor until 1952. By 1955 there were 100 FM transmitters in operation. With a severe shortage of medium wave frequencies, Italy followed suit, providing its first VHF radio services in the early 1950s.

At about the same time, other European nations, working through the European Broadcasting Union (EBU), began to reconsider FM's potential, because they had largely completed the process of repairing or replacing wartime AM radio losses. FM was seen as the only means of reducing serious medium wave overcrowding and resulting interference problems as well as serving regions largely unreached by existing stations, and FM could do so less expensively than could medium wave facilities. Countries also sought additional program channels. Interestingly, the same debate over whether FM should carry the same or different programs (as existing medium wave services) divided industries and governments in Europe as it had in the United States. By the late 1950s, EBU member nations were working together to build a system integrating existing and new VHF radio stations. And, as in the United States, the new services were increasingly programmed independently.

After experimenting with FM in London as early as 1950, the British Broadcasting Company (BBC) began introducing a chain of VHF radio stations in 1955. By 1960, most of the country was reached with the new transmitters, which largely simulcasted the medium wave station signals, though receiver penetration hovered at only about 15 percent, rising to 30 percent five years later. The planned role of the VHF transmitters was to introduce local programming for specific audiences-something that had been lacking in Britain since the early 1920s. By the early 1960s, VHF radio transmitters outnumbered medium wave facilities by 160 to 57. A decade later, there were 252 VHF transmitters in Britain. Lower FM receiver prices prompted rapid ownership growth.

Even by the mid-198os, however, only about 20 countries (most of them in Europe) had extensively developed VHF radio. Despite its potential value to tropical countries, which are plagued by static on their AM or medium wave broadcast stations, few Third World nations had embarked on FM service. They lack the funds and even the need, because they have not fully utilized available medium wave channels. South Africa is an exception, having embarked in 1961 on development of VHF radio to cover the nation. Apartheid politics may have played a role here, because the VHF transmitters made it more difficult for Africans to hear foreign broadcasts, none of which were available on FM. Other African nations only experimented with FM in this period.

In the Far East, Japan experimented with FM for a decade before stations opened in major cities in 1969. The Ministry of Posts and Telecommunications sought to have an FM station in every prefecture and at least two in major cities. All of these are advertising-supported local stations. For a time in the 1970s and 1980s, a raft of mini-FM transmitters called "free radio," which covered a radius of only about 3,000 feet, were very popular, playing music and advertising. Few were licensed, however, and many were closed down in the late 1980s. The service came later to Australia, where what would become FM frequencies had been originally allocated to television. Reallocation of that service made initiation of FM Service possible there in the 1980s.

Perhaps the most extreme examples of the FM-based "free radio" movement took place in the 1970s in both France and Italy. A number of unlicensed small local Italian FM stations went on the air in late 1974 and into 1975. When an Italian court held that the state broadcasting authority did not have a monopoly on local radio, hundreds more followed in 1976. By mid-1978, some 2,200 were on the air, providing Italians with the most radio per capita of any nation on earth. Stations programmed music and advertising and often expressed strong political viewpoints on both the right and left. France went through something similar in the late 1970s-by the early 1980s there were more than 100 such stations in Paris alone. Most gave way to a 1982 government decision to provide licenses to many of the stations as well as official permission to advertise.