Repack Complexities Abound

February 22, 2017

As I write this, Stage 4 of the reverse auction has ended and it appears likely the UHF broadcast TV band will be reduced to Channels 14–36 (470– 608 MHz). When UHF spectrum was originally opened for broadcasting, it occupied Channels 14–83 (470–890 MHz), with Channel 37 reserved for radio astronomy and wireless medical devices. Broadcasters gave up Channels 70–83 in 1970. In 2009, TV broadcasters, again at their own cost, returned spectrum from Channel 52 to 69 to the FCC.

This time, broadcasters will be reimbursed for most of the cost of changing to a new channel, but the repack will be more complicated. One reason is that tower standards have changed significantly since the first DTV antennas were installed.

Another reason is that broadcasters will have limited flexibility in modifying antenna patterns, potentially limiting options. Translator and LPTV stations won’t be assigned a new channel and won’t be reimbursed for the cost of the channel change—they will have to compete with other translator and LPTV licensees for the limited number of channels left after full-power and Class A TV stations are packed into the channels below 37.

Stations needing to replace antennas may find they cannot get a permit to modify their antennas unless towers are upgraded to TIA standard 222-G. Many towers were built when the “F” standard was in place and may not meet the requirements for “G.” The “G” standard takes local conditions into account, so towers on mountaintops and in areas subject to icing are particularly affected by the revision. It’s possible the “H” version of the standard will be implemented before the repack is complete. If the tower has to be replaced, an environmental impact study may be required. While such a study isn’t likely to be an issue in an area with multiple towers, it takes time. If there is local opposition, approval could take a long time.

The FCC will assign stations an antenna pattern. In most, if not all cases, it will match the station’s existing antenna pattern. The problem is that antenna patterns change with frequency. The difference is usually the depth and location of nulls and side lobes. These can be significant and are likely to fall outside the limited changes allowed for a “checklist” application.

Another issue is antenna height. To maintain the same elevation pattern and gain, an antenna for a lower channel will require more aperture. If the antenna is top mounted, this is likely to put it above the FAA approved tower height. Getting approval to increase tower height can be a lengthy process, as can physically reducing the height of a tower. However, if a station is moving to a substantially lower channel, a lower gain (shorter) antenna may work as the authorized power will drop.

The field strength of a UHF station’s FCC contour varies with frequency. It is 41 dBμV/m in the center of the band at 615 MHz, decreases for channels below 37, and increases for channels above 37. Stations moving from above Channel 36 will find their ERP is reduced. The table shows the percentage ERP reduction required for stations moving from a higher to lower channel. While I’ve only shown existing channels above 37, the adjustment will also apply to stations moving within the Channel 14–36 band. A station moving from Channel 14 to 36, for example, would have to increase its ERP by approximately 30 percent to maintain its contour. Stations with an ERP at or near the 1,000 kW limit that are repacked to a higher channel will lose coverage.

Preparing E.R.P. reduction required to maintain FCC contour changing to a lower channel from Channels 38–51

I’ve heard the FCC will reimburse stations for auxiliary antennas required for the transition, even if they don’t have a currently licensed auxiliary facility. This makes sense, as without a second antenna, a station would have to go off air while the old antenna is removed and the new antenna is installed. If the transition to the new channel is delayed, as is likely to happen in several markets due to the tower issues noted earlier, then the station could be off the air for a long time if it were not able to begin operation early on the new channel.

Timing of the transition to new channels adds complexity. Depending on the number of stations in a market that have to change channels, and the daisy chain of stations in surrounding markets impacted by the changes, the actual date of the transition is unlikely to be known until construction of facilities—either main or auxiliary—on the new channels is completed for all affected stations in all markets in the daisy chain.

Timing will impact station’s repack plans. Stations should have full coverage on their new channels when the market re-scans take place. For this reason, I recommend building out an adequate auxiliary facility on the pre-repack channel so the prime antenna location can be cleared for installation of the antenna for the new channel. There is likely to be some reduction in pre-repack coverage, but viewers will already have the channel saved in their tuners and can be educated before the switch to adjust or upgrade their antennas to get the channel back.

Stations have several options for auxiliary antennas. An existing adequate auxiliary antenna may be sufficient. In some markets, American Tower is building or already has broadband antenna facilities for lease, if they cover the channels required. Note that panel antenna systems are not alike. Some existing systems will not work at lower UHF channels and newer systems built for the transition may not support upper UHF channels, limiting their usefulness for post-repack and pre-repack use, respectively.

A broadband auxiliary antenna may make sense as it can be used on both pre-repack and post-repack channels if there are delays in erecting the final DTV antenna.

Dielectric’s TFU-WB and the RFS SBB series look attractive. As I mentioned with the panel antennas, be sure to confirm the antenna will work on existing and post-repack channels. Finally, side mount antennas such as ERI’s ALP series and Dielectric’s TLP line are lightweight, low cost, and available in a much wider range of patterns. These could be a viable option if a broadband antenna won’t work.

Due to their size, swapping out one of them for another on a different channel shouldn’t require extensive tower rigging. The final swap-out may be able to be done in one day, minimizing off-air time. Allow extra time for assembling the antenna and checking it once installed.

Temporary channel-sharing is another option. If enough stations remain after the auction, when a station having difficulty constructing its new facilities may be able to share bandwidth on a station that isn’t changing channels or has completed repack construction. This will impact picture quality, but the trade-off may be worth it to maintain coverage.

I hope these suggestions have been useful. If you have other ideas or unique plans for the repack, please let me know!

Email me at [email protected].

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