NAB, MSTV and Networks Support FCC DTV Signal Measurement Plan
August 17, 2006
The NAB, along with ABC, CBS and NBC affiliate associations and the Association for Maximum Service Television (MSTV) have filed comments in the FCC Notice of Proposed Rule Making (NPRM) on measurement standards for digital signal strength testing for the purpose of determining whether a household is served by local DTV stations under the Satellite Home Viewer Extension and Reauthorization Act (SHVERA). In their initial comments, they supported the FCC proposals with a few exceptions.
Broadcasters told the FCC that it should require use of a calibrated gain antenna rather than a dipole antenna, noting that a gain antenna allows use of less sensitive measurement equipment and is much less subject to multipath than a dipole. They point out that not only is a log-periodic antenna easier to use as it does not have to be readjusted for each channel measured -- the dipole's length has to be changed for each channel -- but that it is also less expensive than a NIST-traceable dipole. The engineering statement from Meintel, Sgrignoli and Wallace (MSW) included in the filing, notes the price of a NIST-traceable dipole ranges from $1,300 to $2,100 from various manufacturers. They suggest using an antenna such as the Scala/Kathrein CL-1469 log periodic antenna, which costs only $468, and provides a "reasonably flat gain characteristic of about 8 dB across the UHF television band." MSW suggests the manufacturers can provide gain antennas that have been calibrated against a known dipole or NIST-traceable antenna. Alternatively, they say an antenna manufacturer could provide a certified antenna chart specifying that it certifies the gain of the antenna at specific channels.
NAB and the broadcasters agreed with the FCC's conclusion that the DTV signal be measured as the integrated power over the 6 MHz channel bandwidth of the DTV signal. While rejecting the use of current analog field strength meters, which have very narrow IF bandwidths, NAB and the broadcasters recommended the FCC adopt a maximum IF bandwidth no greater than 100 KHz, noting that if wider bandwidths are used, it could lead to inaccurate measurements when adjacent channel signals are present.
The comments also addressed data recording methods. NAB and the broadcasters recommend that testers follow standardized data recording methods. They offered to provide an Excel spreadsheet template developed by MSW that allows a tester to complete the measurements using the instruments described in MSW's statement and easily convert these to Median Field Strength, without the need for complex formulas and development of their own spreadsheet.
The MSW engineering statement, in Appendix A, provides suggested methodology for conducting DTV field strength measurements. Broadcasters interested in checking their DTV coverage at specific locations should find this useful, even if the FCC does not formally adopt it for the SHERVA measurements.