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FCC lays out procedure for DTV field strength measurements

The FCC established Nov. 22 procedures to measure the field strength of DTV signals for the purpose of determining whether a satellite TV provider may import an out-of-market network TV station in any given location. The new procedures were made public Nov. 23.

The procedures, laid out in an FCC Report and Order, address a key provision of the Satellite Television Extension and Localism Act of 2010 (STELA), namely measuring DTV signal strength with one of the three methods that can be used to determine whether a distant network station can be retransmitted via satellite to viewers in a specific locale.

The new rules address specific test parameters, including the location of the measurement antenna, antenna height, signal measurement method, antenna orientation and polarization, and data recording.

The Report and Order calls for the continued used of the same rules for measuring DTV signals as the commission used for measuring analog TV signals, with a few notable exceptions. One area of difference is the actual measurement of signal strength. The Report and Order requires tests that measure the integrated average power over a DTV signal’s entire 6MHz bandwidth. Additionally, the measuring instrument’s intermediate frequency bandwidth can be no greater than 6MHz. However, the rules recommend that the measurement instrument use an intermediate frequency bandwidth of 100kHz, unless the instrument “is specifically designed to use an alternative IF bandwidth.”

The commission, which declined to include indoor DTV antenna signal strength measurement in the rules, also addressed outdoor antenna height by maintaining its existing rules. For one-story structures, the measurement is to be made 20ft above ground; for taller structures, the measurement is to be made at 30ft.

Where to measure at the antenna or future antenna location did not change. Existing rules require five cluster measurements to be taken, each of which should be 9.84ft apart, if possible. The first measurement is supposed to be in the center of a square with the four remaining measurements made at the square’s corners. The Report and Order clarified the rules to explicitly state that a square pattern must be used only if doing so is possible.

Other aspects of the procedures to be used that remained identical to the analog TV measurement procedures include

  • use of shielded transmission line;
  • matching the antenna impedance to the transmission line at all measured frequencies;
  • use of a suitable blaun when an unbalanced line is used;
  • measurement of transmission line loss at each frequency; and
  • use of a horizontally polarized antenna facing the strongest signal being transmitted from the transmitter.

Other provisions include giving testers the flexibility to use a half-wave dipole or a gain antenna when carrying out the DTV field strength measurements; barring field strength tests during inclement weather; and allowing the use of the same measurement data recording requirements employed when measuring analog signals strength.

The Report and Order was one of four actions taken by the commission last month to implement STELA. The others included revising the rules determining what constitutes a “significantly viewed” channel to level the playing field between cable and satellite TV operators; adoption of a point-to-point predictive model for determining whether over-the-air DTV broadcast signals can be received with an antenna at individual locations at the intensity level needed for service; and a public notice seeking comment and data to help the commission prepare a Congressionally mandated report by Aug. 27, 2011, on in-state broadcast programming.