04.11.2007 03:35 PM
DTV receivers susceptible to adjacent channel interference

The FCC Office of Engineering and Technology (OET) released a report late last month based on testing of DTV receivers to determine their interference rejection characteristics.

The test, conducted by the OET’s Technical Research Branch Laboratory Division, aimed to find out, among other things, how susceptible DTV receivers would be to adjacent channel interference from the sorts of devices seeking to use TV spectrum white spaces, or unoccupied TV spectrum in a given locality.

The tests were performed in the UHF band. Most were done with the DTV tuned to channel 30. Some early tests were done on channel 51. According to the report, measurements on channel 51 “generally matched those on channel 30 within about 4 dB — and in most instances much closer than that.”

The report found that if channel 30 were designated “N:”

  • DTV receivers “tend to be more susceptible to interference from N+2, N+1, N-1, N-2, N-3, N-4 and sometimes N-6 than from the mixer image channel offsets of N+14 and N+15;”
  • At moderate levels of desired signal strength, “the receivers exhibit relatively high susceptibility to interference from channel N+7;”
  • At lower levels of desired signal strength, “other channel offsets become more vulnerable.”

For a perspective on what such interference could mean to the success of the DTV transition, read: “DTV transition goal:no viewer should be left behind, Donovan says."

To read the report in its entirety, visit: http://www.fcc.gov/oet/info/documents/reports/DTV_Interference_Rejection_Thresholds-03-30-07.doc.

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