Clashing Financial Markets
In the world of radio broadcasting, one issue that has long been a challenge is the occurrence of FM signal collisions and adjacent spillover. These phenomena are particularly prevalent in areas with dense FM station clustering, international or state boundaries, and complex terrain.
A prime example of this can be found in urban and metropolitan areas, where many FM stations broadcast on closely spaced frequencies at high power. This can result in adjacent channel spillover and, occasionally, direct frequency collisions if station assignments are not perfectly coordinated.
Border regions between different countries or regulatory zones also present a significant challenge. When two countries independently allocate FM stations near their mutual border, overlapping signals on the same or adjacent frequencies can cause collisions or spillover effects because the stations' transmitters may be physically close across the border.
Mountainous or variable terrain areas also pose a problem due to propagation reflections and refractions. Signals from stations farther away can unexpectedly overlap with local stations, resulting in multipath interference and spillover.
Co-located FM transmitters or mast sites hosting multiple stations can also lead to signal leakage or collisions if transmitters on the same tower or in the same facility are not properly filtered or spaced in frequency.
The Northeast region, specifically New Jersey, offers more opportunities for adjacent spillover due to the tighter spacings of FM stations, which are classified as Zones I and I-A by the FCC. Two Class B FM stations in New Jersey, 94.5 WPST(FM) and 94.7 WXBK(FM), are approximately 58 miles apart.
In New York City and Philadelphia, the FMs typically follow an 800 kHz separation pattern. For instance, 101.9 WFAN(FM) is 200 kHz below 102.1 WIOQ(FM). When a signal is 6 dB weaker than a first-adjacent FM signal, it becomes subject to adjacent spillover.
Older receivers found it challenging to hear a weaker signal 200 kHz away from a stronger one. This issue has been notably improved with the advent of DSP-generated selectivity in modern car radio tuners and portables.
The proximity of these short-spaced FM stations in the Northeast has led to the coexistence of their signals over the years with the aid of directional antennas. An example of this close-quarters setup can be seen in 103.3 WPRB(FM) in Princeton and 103.5 WKTU(FM) in New York, though licensed to different locations.
In portions of Mercer, Hunterdon, and Middlesex counties, the signals of New York City and Philadelphia FMs can be equal in strength, allowing poorer selectivity portables to hear both stations.
If there are any examples of locations where full-power signals collide or where adjacent channel spillover occurs, the reader is encouraged to share them. These phenomena represent practical challenges in radio spectrum management to ensure minimal interference among stations.
The Longley-Rice method can be used to find locations where both New York City and Philadelphia FMs register with about a 60 dBuV/m predicted signal field strength. Similarly, the effect of adjacent spillover in the areas between Los Angeles and San Diego is presumed to be similar to other regions with close proximity between major cities.
The phenomenon of adjacent spillover was part of the motivation for the development of the RadioLand app. If you need concrete case studies or specific city examples, such examples are usually documented in broadcast regulatory filings or technical forums relating to frequency coordination in the FM band. Common real-world reports include interference zones around border cities such as San Diego-Tijuana (US-Mexico) or between cities in Europe with dense FM allocations.
- Technology advancements in modern car radio tuners and portables have significantly improved the ability to hear weaker signals that are 200 kHz away from stronger ones, a problem often encountered in areas with dense FM station clustering, such as the Northeast.
- The coexistence of short-spaced FM stations in the Northeast, like 103.3 WPRB(FM) in Princeton and 103.5 WKTU(FM) in New York, have been made possible over the years with the aid of directional antennas, helping to reduce signal collisions and adjacent spillover.
- In border regions between different countries or regulatory zones, such as San Diego-Tijuana (US-Mexico) and certain cities in Europe with dense FM allocations, overlapping signals on the same or adjacent frequencies can cause significant collisions or spillover effects, posing practical challenges in radio spectrum management.
