UHF television broadcasting

Bandwidth for television in the United States was allocated by the Federal Communications Commission (FCC) in 1937, solely in the VHF (Very High Frequency) band, across 18 channels.[8] American television broadcasting began experimentally in the 1930s with regular commercial broadcasting in cities such as New York and Chicago in 1941. Efforts at TV broadcasting on any channel were drastically curtailed once World War II began, due largely to lack of available receivers. The upper five VHF channels were removed from the FCC allocation list during the war with those frequencies re-allocated for military use, leaving thirteen channels (1 through 13) as of May 1945.[9]

The end of the war brought rapid expansion in the nascent broadcast television industry. Thirteen VHF channels was found to be insufficient to support the desired expansion of broadcast television across the United States. Interference and channel crowding in densely populated areas (such as the eastern mid-Atlantic states) was a particular problem. This bandwidth crunch was made even worse by the need to re-allocate VHF Channel 1 to land-mobile radio systems in 1948 due to radio-interference problems. To illustrate the channel crowding problem, the following cities were never allocated any VHF-TV stations at all, due to technical reasons found by the FCC: Huntsville, Alabama; Peoria, Illinois; Fort Wayne, Indiana; South Bend, Indiana, Lexington, Kentucky; Springfield, Massachusetts; Elmira, New York; Youngstown, Ohio; Scranton/Wilkes-Barre, Pennsylvania; and Yakima, Washington. Other cites were able to receive only one VHF broadcast station. The entire state of New Jersey would receive only one VHF broadcast station of its own (which was to ultimately become WNET 13 Newark). Similarly, Delaware also had only one VHF station.

Meanwhile, UHF broadcasting until 1949 was designated as experimental. In the fall of 1944, the Columbia Broadcasting System proposed a high-definition black and white system on the UHF band employing 750–1,000 scanning lines that offered the possibility of higher-definition monochrome and color broadcasting, both then were precluded from the VHF band because of their bandwidth demands; more significantly, it offered the possibility for sufficient numbers of conventional 6 MHz channels to support the FCC's goals of a "truly nationwide and competitive service". CBS was not trying to maximize broadcast (or network) competition through freer market entry. Instead CBS's 16 MHz channels would have allowed only 27 UHF channels versus the 82 channels possible under the standard 6 MHz bandwidth. CBS Vice President Adrian Murphy told the FCC: "I would say that it would be better to have two networks in color" instead of the four or more networks possible with narrower bandwidths in UHF.[9]

In October 1948, the Federal Communications Commission stopped accepting applications for new stations, a freeze expected to last "six months to a year".[8] The freeze would give the FCC and broadcasting interests time to address questions such as the allocation of additional channel frequencies, and the selection of a color television standard. At the time of the freeze, less than 100 stations were on the air, but stations already under construction would be allowed to complete work. All but one of these was on the VHF band; on December 29, 1949, KC2XAK of Bridgeport, Connecticut, became the first and only pre-1950 UHF television station to operate on a regular daily schedule. Existing FCC rules at the time of the freeze had designated 42 UHF channels, designated 14–55, between 475–890 MHz.

Ultimately, the question the FCC faced of how to allocate bandwidth for new television licenses would not take "months" to resolve, but several years. To newer entrants into TV broadcasting such as the American Broadcasting Company and DuMont Television Network, the need for additional TV channels in major markets was urgent.[10] For proponents of educational TV broadcasting, the difficulties in competing with commercial broadcasters for the increasingly scarce VHF channels was also a problem.[11]

Allocating more of the VHF band (30 to 300 MHz) by moving existing radio communication users away seemed to be impossible. FM radio broadcasting had already suffered a huge setback after a forced move from a 42–50 MHz allocation to an 88–108 MHz allocation in 1946.[12] This had rendered all pre-1946 FM transmitters and receivers obsolete, and there was heavy resistance to moving FM a second time. Aeronautical radio is located above 108 MHz; military aeronautical radio used 225–400 MHz. Additional public safety, commercial land-mobile, and amateur radio services had allocations in Band II. It was impractical and uneconomic to require these well-established VHF users to move to other frequencies, such as the 300 MHz – 3 GHz UHF band.

All of this made expansion of broadcast television channels into the UHF band inevitable, though the technology and broadcasting characteristics of UHF was at this time largely unproven. Even the television standard to use to broadcast on UHF was in question at the time of the 1948 FCC freeze.

With the knowledge that UHF channel allocation would be necessary to expand television coverage, and with the knowledge that by 1949 VHF television was an entrenched standard, the FCC proposed intermixture, licensing both VHF and UHF stations in a single city. Intermixture would rely on consumers rapidly adopting television sets with UHF tuning capability, and on the base assumption that a UHF television station was functionally equivalent to a VHF one. To allocate four to as many as seven VHF channels to each of the largest cities would mean forcing the smaller, intervening cities completely onto UHF channels, while an allocation scheme that sought to assign one or two VHF channels in each smaller city would force VHF and UHF stations to compete in most markets. The largest cities with the most sets in use benefitted most from VHF allocations. For example, New York City, Washington-Baltimore, Los Angeles, and San Francisco received seven VHF stations apiece, and Chicago was allocated five, with the other two of those channels going to Milwaukee, Wisconsin and Rockford, Illinois.

FCC rules published on April 11, 1952, defined the final modern-day UHF allocation of 70 channels, 14 through 83, with 6 MHz separation. It used standard NTSC standards.[13] This would allow the license freeze enacted in 1949 to end. Through the entire three-and-a-half year freeze period, KC2XAK remained the only UHF television station in regular operation.[14]

When the FCC television license freeze ended in 1952, a huge backlog of potential stations applied, many allocated to the UHF band as defined by the 1952 rules. The first commercially licensed UHF television station was WWLP in Springfield, Massachusetts;[15] however, the first commercial UHF television station on the air was KPTV, Channel 27, in Portland, Oregon, on September 18, 1952. Early in 1953, 35% of televisions sold contained a UHF tuner compliant with 1952 rules, lending hope to the idea that intermixture of UHF and VHF stations might succeed.

Several problems with early UHF tuners became evident. One was poor image frequency rejection in superheterodyne receivers with the standard intermediate frequency of 45.75 MHz. Another was very poor adjacent-channel rejection and channel selectivity by early tuner designs and manufactures. These problems were so significant that UHF-TV stations in the same geographic area were usually assigned a minimum of six channels apart from one another. Technical problems with the design of vacuum tubes for operation at high UHF frequencies were beginning to be addressed in 1954,[16] but in the meantime, these shortcomings led to "UHF taboos", which in effect limited each metropolitan area to only moderately more UHF stations than VHF ones, despite the much higher number of channels.[17]

Television sets in the United States were not mandated to include UHF tuners until 1964. With UHF's reputation for reception problems, the fraction of new TV receivers that were factory-equipped with all-channel tuners dropped from 35% in early 1953 to 9% by 1958, a drop that was only partially compensated for by field upgrades or the availability of external UHF converters for separate purchase. Plummeting inclusion of UHF tuners in sets placed VHF–UHF intermixture at grave risk of failure.

UHF converters on display at the Early Television Museum

On the transmission side, UHF stations were also found to have issues involving transmission distance and strength. The FCC tried solving this problem by allowing the lower powered UHF stations to broadcast with more power, but VHF continued to have more stations. Advertisers soon caught on to this and did most of their business with VHF stations since UHF tuner adoption was flagging.[18] While the more-established broadcasters were operating profitably on VHF channels as affiliates of the two largest TV networks (at the time, NBC and CBS), most of the original UHF local stations of the 1950s soon went bankrupt, limited by the range their signals could travel, the lack of UHF tuners in most TV sets and the paucity of advertisers willing to spend money on them. UHF stations fell quickly behind the VHF stations, losing $10,500,000 in 1953. More stations left the air than opened, and sixty percent of television industry losses from 1953 to 1956 came from UHF stations.[9] TV network affiliations were difficult to get in many locations; the UHF stations with major-network affiliation would often lose these affiliations in favor of any viable new VHF TV station that entered the same market. Of the 82 new UHF-TV stations in the United States broadcasting as of June 1954, only 24 of them remained a year later.[19]

The majority of the 165 UHF stations to begin telecasting between 1952 and 1959 did not survive. Not until the passage of the 1962 All-Channel Receiver Act did FCC regulations require all new TV sets sold in the U.S. after April 30, 1964 to have built-in UHF tuners that could receive channels 14–83. In spite of this, by 1971, only about 170 full-service UHF stations were in operation.[20]

In the United States, UHF stations gained a reputation for local ownership, nonprofessional operations, small audiences and weak signal propagation.

While UHF-TV was available to American TV broadcasters in today's form since 1952, affiliates of the 1950s four largest American TV networks (NBC, CBS, ABC, and DuMont) preferentially transmitted on VHF wherever it was available. All available VHF-TV allocations were already in use in most large TV markets by the mid-1950s, owing to FCC spacing rules to avoid co-channel and adjacent channel interference between VHF TV stations in the same or nearby cities. Two VHF TV stations on the same channel needed to be 160 or more miles apart, and two VHF TV stations on adjacent channel frequencies needed to be 60 or more miles apart.

UHF stations in major population centers of the United States were usually either educational network or independent TV stations.[21] The movie UHF (starring "Weird Al" Yankovic and Michael Richards) parodied the independent UHF station phenomenon;[22] a fictional UHF station was also parodied in the 1980 film Pray TV. Some cities did develop successful independent UHF stations, many of these located in or near state capital cities, or served by nearby major rural regions. These included Montgomery, Alabama; Frankfort, Kentucky; Dover, Delaware; Lincoln, Nebraska; Topeka, Kansas; Jefferson City, Missouri; Lansing, Michigan; Harrisburg, Pennsylvania; Madison, Wisconsin; and Springfield, Illinois. In the United States, television stations in or near state capital cities are important because they closely covered the operations of state governments and spread information to residents across their state.

TV antenna manufacturers often rated their top-of-the-line "deep-fringe" antenna models with phrases like "100 miles VHF/60 miles UHF" if the antenna included UHF reception at all. (In the practice of electrical engineering, the frequency range in which an antenna is to be used is an important factor in its design.)

TV set manufacturers often treated UHF tuners as extra-charge optional-items until they became required. Various FCC attempts to protect UHF stations were met with mixed results.

• Limits on the number of owned-and-operated stations controlled by one corporation were raised from five stations to seven, provided that two of them were UHF stations. Both NBC-TV (WBUF 17 Buffalo, WNBC 30 Hartford) and CBS-TV (WHCT 18 Hartford, WXIX 19 Milwaukee) acquired pairs of UHF stations as an experiment in the mid-1950s, only to abandon the stations in 1958–9. (NBC has since reacquired channel 30 in Hartford, now WVIT.) Their commercial network programming soon returned to VHF channel affiliates. WBUF's facility on channel 17 was donated to start WNED-TV, a Public Broadcasting Service station. KPTV abandoned UHF for VHF channel 12 after merging its license and intellectual unit onto the channel 12 allocation with another broadcaster.[23]
• The UHF television impact policy (1960–1988) allowed applications for new VHF TV stations to be opposed in cases where licensure could lead to the economic failure of an existing UHF TV broadcaster.[24]
• The secondary affiliation rule (1971–1995) prohibited a network entering a market with two existing VHF TV network affiliates and one UHF independent TV station from placing its programs on a secondary basis on one or both VHF stations without offering them to the UHF station.[25]
• Limits on UHF effective radiated power, originally very restrictive, were relaxed. A UHF TV station could be licensed for up to five megawatts of carrier power, unlike VHF TV stations, which were limited to 100 (Channels 2–6) or 316 kilowatts of carrier power (Channels 7–13) depending on their channel.
• More recent limits on station ownership are based on the combined percentage of the American population (originally 35% maximum, now increased to 45%) reached by one group of stations under common ownership. A UHF discount, by which only half of the audience of a UHF station would be counted against these limits, would ultimately allow groups such as PAX to reach the majority of the American audience using owned-and-operated UHF stations.[26]

The situation began to improve in the 1960s and 1970s, but progress was slow and difficult.

While the smaller ABC-TV and DuMont Networks had a number of UHF affiliates,[27] National Educational Television and its successor, PBS had even more.

The original SIN (Spanish International Network) was established in 1962 as the predecessor of the modern Univision network. It was built primarily by UHF stations, such as KWEX-TV, Channel 41 in San Antonio and KMEX-TV, Channel 34 in Los Angeles.

In 1970, Ted Turner acquired a struggling independent station on Channel 17 in Atlanta, Georgia, purchasing reruns of popular television shows, the Atlanta Braves baseball team and the Atlanta Hawks basketball team.

This station, renamed WTBS, was uplinked in 1976 to satellite alongside new premium channels such as HBO, gaining access to distant cable television markets and becoming the first of various superstations to obtain national coverage. In 1986, Turner purchased the entire MGM film library. Turner Broadcasting System's access to movie rights proved commercially valuable as home video cassette rental became ubiquitous in the 1980s.

In 1986, the DuMont owned-and-operated station group Metromedia was acquired by News Corporation and used as the foundation to relaunch a fourth commercial network, which obtained affiliations with many former big-city independent stations as Fox TV.

Fox initially combined former independents and UHF stations. It had large programming budgets that the original DuMont lacked. Ultimately, it was able in some markets to draw existing VHF affiliates away from established Big Three networks, outbidding CBS for National Football Conference programming in 1994 and attracting many of that network's affiliates. Various smaller networks were created with the intent to follow in its footsteps, often by affiliating with a disparate collection of formerly independent UHF stations that otherwise would have no network programming.

By 1994, New World Communications was moving its established stations from CBS to Fox affiliations in multiple markets, including WJBK-TV 2 Detroit. In many cases, this pushed CBS onto UHF; "U-62" as the new home of CBS in Detroit became CBS owned-and-operated station WWJ-TV in 1995, obtaining access to audiences thousands of miles distant through satellite and cable television.

The concentration of media ownership, the proliferation of cable and satellite television and the digital television transition contributed to the quality equalization of VHF and UHF broadcasts. The distinction between UHF and VHF characteristics declined in importance with the emergence of additional broadcast television networks (Fox, The CW, MyNetworkTV, Univision, Telemundo, and UniMás), and the decline of direct OTA reception. The number of major large-city independent stations also declined as many joined or formed new networks.

The majority of digital TV stations currently broadcast in the UHF band, both because VHF was already filled largely with analog TV when the digital facilities were built and because of severe issues with impulse noise on digital low-VHF channels. While virtual channel numbering schemes routinely display channel numbers like "2.1" or "6.1" for individual North American terrestrial HDTV broadcasts, these are more often than not actually UHF signals. Many equipment vendors therefore use "HDTV antenna" or similar branding as all but synonymous to "UHF antenna".

Terrestrial digital television is based on a forward error correction scheme, in which a channel is assumed to have a random bit error rate and additional data bits may be sent to allow these errors to be corrected at the receiver. While this error correction can work well in the UHF band where the interference consist largely of white noise, it has largely proven inadequate on lower VHF channels where bursts of impulse noise disrupt the entire channel for short lengths of time. A short impulse-noise burst might be a minor annoyance to analog TV viewers, but due to the fixed timing and repetitive nature of analog video synchronization is usually recoverable. The same interference can prove severe enough to prevent the reliable reception of the more fragile and more highly compressed ATSC digital television. Power limits are also lower on low-VHF; a digital UHF station may be licensed to transmit up to a megawatt of effective radiated power. Very few stations returned to VHF channels 2–6 after the transition was completed in 2009, and were mainly concentrated in the Desert Southwest and Mountain West regions, where few geographical obstructions and adjoining co-channel stations exist. At least three quarters of all full-power digital broadcasts continued to use UHF transmitters, with most of the others located on the high-VHF channels. In some American markets, such as Syracuse, New York, no full-service VHF TV stations remained.

The one remaining limitation of UHF is its greatly reduced range in the presence of terrain obstacles. This continues to adversely affect digital UHF TV reception. This limitation could potentially be overcome by the use of a distributed transmission system. Multiple digital UHF transmitters in carefully selected locations can be synchronized as a single-frequency network to produce a tailored coverage area pattern rivaling that of a single full-power VHF transmitter.

Due to the inferiority of UHF broadcasting for analog television, the FCC counts the audience of UHF stations by half for the purposes of its national market share cap of 39%, a policy known as the UHF discount. The rule was briefly removed in September 2016, with the FCC citing that the rule was obsolete because almost all digital television channels are on the UHF band, and that the policy was being abused by broadcasters as a loophole to increase their market share.[28][29][30] However, in April 2017, under new FCC commissioner Ajit Pai, the discount was reinstated.[31][32]

One notable exception to historical patterns favoring VHF broadcasters has existed in television markets that could not qualify for their own VHF stations because they were sandwiched between the outer fringes of VHF stations in two or more larger markets. Such cities received only UHF licenses.

With all stations (including network affiliates) on UHF, all-channel receivers and antennas became commonplace locally and UHF stations signing on as early as 1953 were often able to obtain the programming and audience needed to remain viable into the modern era.[33]

These communities, known as UHF islands, included cities like Youngstown, Ohio; Tri-Cities, Washington; Springfield, Massachusetts; Elmira, New York; South Bend, Indiana; Fort Wayne, Indiana; Peoria, Illinois; Huntsville, Alabama; Salisbury, Maryland; Lexington, Kentucky; and Scranton, Pennsylvania. Other smaller cities such as Madison, Wisconsin; Bakersfield, California; Fresno, California; Fort Myers, Florida; Mankato, Minnesota; Watertown, New York; Erie, Pennsylvania; Columbia, South Carolina; and Harrisburg, Pennsylvania only received one VHF license, meaning that any additional programming would need to be provided either by UHF, by distant stations, or by low-power broadcasting. The Bakersfield and Fresno markets originally had stations that operated on a VHF channel (KERO-TV on channel 10 and KFRE-TV on channel 12); those markets became UHF islands between 1961 and 1963 after the FCC initiated a deintermixture process, with KERO-TV moving to channel 23 and KFRE-TV moving to channel 30.[34][35] The allocations of the two channels that were vacated were reassigned to nearby markets; channel 10 would be reallocated to the Las Vegas, Nevada market as a fifth VHF channel (which would be used by KLVX when it signed on in 1968), while channel 12 would be reallocated to the Santa Barbara, California market as a third VHF channel (which would be used by KCOY-TV when it signed on in 1964).

Very small UHF TV transmitters continue to operate with no programming or commercial identity, instead retransmitting signals of existing full-power stations to a smaller area poorly covered by the main VHF signal. Such transmitters are called "translators" rather than "stations". The smallest, owned by local municipal-level groups or the originating TV stations, are numbered sequentially – W or K, followed by the channel number, followed by two sequentially issued letters, yielding a "translator callsign" in a generic format that appears K14AA through W69ZZ. Translators and repeaters also exist on VHF channels, but infrequently and with stringently limited power.

The translator band, UHF TV channels 70–83, consisted mostly of these small repeaters; it was removed from television use in 1983 with the tiny repeaters moved primarily to lower UHF channels. The 806–890 MHz band segment is now used primarily by mobile phones. Many of these transmitters, if still in operation, were moved again in 2011 as UHF channels 52–69 were lost primarily to mobile telephony during the DTV transition, and a third time by 2020, when the 2016 wireless spectrum auction eliminated channels 37–51.

As improvements to originating stations lessen the need for these translators, the small transmitter facilities and their allocated frequencies were often repurposed for low-power broadcasting; instead of repeating a distant signal, the tiny transmitter would be used to originate programming for a small local area.