Clash of Financial Markets
In the world of FM radio broadcasting, a unique challenge arises in regions where multiple large metropolitan areas are geographically close, causing their radio signals to overlap and interfere. This phenomenon, known as adjacent spillover interference, is similar to the well-documented cases in New York City and Philadelphia.
In the Midwest, for example, the areas between Chicago and Milwaukee along Lake Michigan experience this phenomenon. Similarly, in the Lake Erie Islands of Ohio, the distance from the FM offerings of Detroit and Cleveland is comparable.
This signal collision occurs because FM stations operate on frequencies spaced closely, usually every 0.2 MHz in the U.S., and when their coverage areas overlap, adjacent-channel interference and spillover occur. Factors such as effective radiated power (ERP), antenna height, terrain, and atmospheric conditions can exacerbate the issue, causing signals to propagate farther than expected and resulting in interference for receivers picking up signals from multiple stations on adjacent or nearby frequencies.
In the United States, such signal collisions are common in densely populated regions where numerous full-power FM stations are close geographically. For instance, the Los Angeles and San Diego areas, two major Southern California metro areas, are relatively close and have many high-power FM stations, leading to some frequency overlap and signal spillover. Similarly, the San Francisco Bay Area and Sacramento, though separated by some distance, have large FM signals from both markets that occasionally encroach into each other’s fringes.
Closer to the East Coast, the Chicago and Milwaukee areas also exhibit this phenomenon, with their full-power FM stations creating interference zones. In the Dallas-Fort Worth Metroplex, the dense concentration of stations can cause adjacent channel spillover locally.
Internationally, densely populated regions such as Greater London and surrounding areas in the UK, Paris and nearby cities in France, and the Tokyo metropolitan area and nearby satellite cities are also prone to this issue due to the extremely high density of FM stations.
The proximity between New York and Philadelphia, both top 10 Nielsen radio markets, makes their dial layouts unique. Two Class B FM stations in New Jersey, 94.5 WPST(FM) and 94.7 WXBK(FM), are located approximately 58 miles apart. In the Beltway area, 105.7 WJZ(FM) from Catonsville, Md., and 105.9 WMAL(FM) from Woodbridge, Va., are two Class B FM stations approximately 48 miles apart. Philadelphia and Baltimore work with a similar setup. WJZ also operates 47 miles from same-channel WQXA(FM) in York, Pa., another Class B station.
In the northeastern U.S., including areas like New Jersey and northeastern Ohio, tighter FM station spacings fall within the FCC’s Zones I and I-A, offering more opportunities for this phenomenon. Central New Jersey, specifically driving up the New Jersey Turnpike near Exit 8A, is a prime example of this phenomenon with the New York City and Philadelphia Class B FMs being about equidistant.
The RadioLand app's work was partly motivated by this phenomenon, and readers are encouraged to share any examples of locations where full-power signals collide. Via the Longley-Rice method, locations like Plainsboro, N.J., can be found where both New York City and Philadelphia FMs register with about a 60 dBuV/m predicted signal field strength. Another close-quarters setup in the region involves 103.3 WPRB(FM) in Princeton and 103.5 WKTU(FM) in New York, transmitting from the Empire State Building.
- The challenge of adjacent spillover interference in FM radio broadcasting also affects regions like the Midwest, where the areas between Chicago and Milwaukee along Lake Michigan experience this phenomenon, due to the close geographical proximity of multiple large cities and the operation of FM stations on frequencies spaced closely.
- Financing for FM stations in densely populated regions, such as the Tokyo metropolitan area and nearby satellite cities, can be challenging due to the high cost of running multiple high-power stations to avoid interference from adjacent channel spillover.
- Science and technology have played a crucial role in combating the issue of adjacent spillover interference in FM radio broadcasting. For example, the RadioLand app uses the Longley-Rice method to predict signal field strength and help identify locations where full-power signals collide.
