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--- adjacent-channel_interference [2023/09/20 14:51] – RabbitEars Webmaster
+++ adjacent-channel_interference [2023/09/20 19:02] (current) – RabbitEars Webmaster
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 ====== Adjacent-Channel Interference ======
-When considering adjacent-channel interference, there isn't a distance requirement with respect to other stations, there's a population impacted requirement, which makes it hard to generalize.  To understand it, it's worth taking a step back to understand how adjacent-channel interference works with digital TV.
+When considering adjacent-channel interference with respect to station facilities and channel assignments, there isn't a distance requirement with respect to other stations, there's a population impacted requirement, which makes it hard to generalize.  To understand it, it's worth taking a step back to understand how adjacent-channel interference works with digital TV.
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 In any event, when the FCC is trying to determine whether or not a station is allowed to exist on an adjacent channel, it does this analysis across a geographic area using the methodology in OET Bulletin No. 69, using the TVStudy software.  The FCC breaks the coverage area of the impacted station into a grid, and each cell of the grid has a representative point where a calculation is done of the signals in question.  If the undesired signal exceeds the threshold with respect to the desired signal, that cell is flagged as having interference.
-Above is a map I made back in 2018, which you can click to expand to its full size.  I used unusual options in TVStudy to create a highly-detailed map, so while the FCC only permits a cell size down to 0.5 km on a side, I used 0.1 km on a side.  The desired station here is WNCN on channel 8.  The purple areas are those where WNCN is calculated to receive interference.  You can see a pretty distinct interference area just south of Goldsboro; these are cells impacted specifically by adjacent-channel interference from WHFL-CD on channel 7.
+Above is a map from 2018, which you can click to expand to its full size.  Unusual options were used in TVStudy to create a highly-detailed map, so while the FCC only permits a cell size down to 0.5 km on a side, this map uses 0.1 km on a side.  The desired station here is WNCN on channel 8.  The purple areas are those where WNCN is predicted to receive interference.  You can see a pretty distinct interference area just south of Goldsboro; these are cells impacted specifically by adjacent-channel interference from WHFL-CD on channel 7.
 Once the analysis of each cell is complete, the population of the flagged cells is added together and divided by the total prior interference-free population.  If the impacted station is a full-service or Class A station, then that number cannot exceed 0.5%.  If it's an LPTV or translator, it cannot exceed 2%.  Stations can negotiate and sign an interference agreement to accept interference in excess of those values, but they can also opt not to negotiate and those FCC-set limits hold.

Any opinions expressed on this site are those of the authors and do not necessarily reflect those of the FCC.