05.10.2006 12:00 AM
Proposed Rules for DTV Signal Strength Tests Build on Analog Test Procedures
After much debate about how to measure DTV signal strengths to determine whether a household is eligible to receive a distant network DTV signal, the FCC has proposed rules that specify procedures similar to those currently in place for measuring analog TV signal strength for determining distant signal eligibility. The FCC did not propose any modification of existing DTV field strength standards or of the DTV planning factors used to establish those standards. The Satellite Home Viewer Extension and Reauthorization Act of 2004 (SHVERA) requires the FCC to set standards for DTV signal strength testing.
"Wherever possible, the proposed procedures rely on existing, proven methods the Commission has established for measuring analog television signal strength at any individual location. We request comment on these proposals," the commission said in its Notice of Proposed Rulemaking (NPRM) FCC 06-51. The commission also asked for input on how to minimize the cost of digital signal strength tests.
The FCC also asked for comments on what type of antenna should be used for DTV signal strength testing. According to the commission, NAB suggested that "measurements be taken using a calibrated gain antenna with a front-to-back ratio consistent with the DTV planning factors." Other options would follow the approach used with analog TV signals and require use of either a standard half-wave dipole antenna or a gain antenna with a known antenna factor for the channels being tested. The FCC said comments on this issue "should provide information to support their position, including technical merits, effect on the accuracy of the measurements, and the practical implications for testing parties, including ease of use and cost."
Analog field strength measurements are fairly simple, as only the visual carrier needs to be measured. DTV measurements are more complicated, because the energy across the entire 6 MHz channel has to be summed to determine the signal level. The FCC proposed requiring "digital signal measurements to be conducted by measuring the integrated average power over the signal's entire 6-megahertz bandwidth." The i.f. bandwidth of the measuring instrument may not be greater than 6 MHz. The FCC noted that average power is usually measured by taking multiple measurements across the TV channel and integrating the results of the individual measurements.
Other proposed measurement procedures are the same as those for analog TV signal measurements.
Since the rules allowing use of digital signal strength testing for determining distant network DTV eligibility went into effect April 30, 2006, the FCC said that the procedures described in the NPRM are to be used for measurements until the final rules are adopted. In this interim period, tests may be conducted using "a calibrated gain antenna with a front-to-back ratio consistent with the commission's DTV planning assumptions, a standard half-wave dipole, or a directional (gain) antenna for which the antenna factor is known."
For complete listing and discussion of all the proposed rules for DTV signal strength testing to determine eligibility to receive distant network signals via satellite under SHVERA, see Notice of Proposed Rulemaking (NPRM) FCC 06-51