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FCC Sets Deadline for LPTV DTV Transition

The FCC has set a hard deadline of September 1, 2015 for the shutdown of all analog low power television facilities, although the Second Report and Order (FCC 11-110) does include rules allowing last minute extensions for stations needing additional time to complete the move to digital. Analog and digital LPTV stations operating above channel 51 must submit displacement applications by September and cease operations above 698 MHz by December 31, 2011.

Finding a new channel for DTV may be difficult, since in the most densely populated areas most UHF channels are already occupied by full service TV stations, other LPTV stations or land-mobile services. Analog LPTV stations that don't have a construction permit (CP) for DTV facilities may find it difficult to transition to digital on their existing channel due to the digital signal's larger desired-to-undesired (D/U) ratio for co-channel interference to an existing DTV station. Co-channel DTV to DTV interference protection requires a D/U of 15 dB compared to only 2 dB for analog to DTV interference where the DTV signal to noise ratio (SNR) is 25 dB or higher, although the D/U for analog LPTV increases to 25 dB where the SNR of the protected DTV signal is only 16 dB.

For some LPTV stations, the only available channel for DTV may be on VHF. At the current maximum ERP of 300 watts, it is very difficult for VHF LPTV stations to provide a reliable signal to indoor antennas. In the Second Report and Order, the FCC increases the ERP for VHF LPTV to 3,000 watts, the same ERP allowed for VHF analog LPTV. This should be good news for LPTV equipment makers as well, since current analog VHF LPTV stations transitioning to DTV on-channel will need to buy a new transmitter or at least additional amplifiers to match their analog peak power ERP.

To make it easier for LPTV stations to find a DTV channel, the FCC modified its minor change rule so that it covers a proposed transmitter site move of up to 30 miles (48 km). LPTV stations will also be able to use the emission mask used by full power TV stations. These two changes should help mitigate the problem of adjacent channel interference to other stations, either by moving to the same transmitter site as the adjacent channel station or using the full service mask to allow reduced D/U ratios. While researching on-channel DTV repeaters at NAB this year I found multiple filter manufacturers making reasonably priced low power DTV filters capable of meeting the FCC full service mask.

To accurately predict interference, actual vertical (elevation) antenna patterns must be used. The Second Report and Order allows LPTV applicants to use actual vertical (elevation) antenna patterns for calculating LPTV coverage and interference. This will benefit stations that employ a large amount of electrical and/or mechanical beam tilt at sites with a large height above average terrain (HAAT). Existing LPTV stations will be able to submit actual vertical patterns for their existing, allowing more accurate interference studies and, depending on the pattern, potentially greater interference protection. This assumes, of course, that the interference study uses the correct depression angle. The default FCC OET-69 software does not although it is now available as an option.

LPTV stations that delay filing applications for DTV or a DTV displacement channel may find few options as the September 1 deadline approaches. The FCC is also likely to freeze TV application filings, at least in major markets before it begins the proposed TV spectrum repacking.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.