In the ongoing debate over reallocation of spectrum at 2 GHz, the FCC last week adopted the innovative channel plan proposed by the Society of Broadcast Engineers (SBE) that divided the remaining broadcast auxiliary service (BAS) spectrum between 2025-2110 into seven 12-MHz wide channels and two 500-KHz wide data return link (DRL) bands.
According to the Third Report and Order and Memorandum Opinion and Order, the new channel plan uses frequency steps compatible with the frequency synthesizers used in most modern 2 GHz radios, reducing the cost of converting them to the new channels. Channel A1r starts at 2025.5 MHz, with channels spaced every 12 MHz through the upper frequency limit of channel A7r at 2109.5 MHz. The original Phase II 2-GHz band plan had a 12.4 MHz wide channel A01 starting at 2025 MHz with 12.1 MHz wide channels above that. Cable television relay stations will be able to use the 7 12-MHz channels but not the DRL bands.
The new Section 74.602(a)(3)(ii) provides for 20 25-KHz wide DRL channels in each 500 KHz segment. The new rules attached to the FCC Order do not specify modulation type or power level or mention whether the channels could be combined for wider bandwidth, higher speed links. A footnote in the text of the Order describes how SBE sees the DRL channels being used: "Since under this proposal there would be 40 DRL channels -- even in a top BAS market with channel splits -- providing 14 ENG channels instead of just seven, SBE avers that there would be a sufficient number of DRL channels to accommodate an enhanced, ATPC mode of operation for all TVPU stations wishing to do so. SBE believes that a 'polite protocol,' where a DRL transmitter steps through each of the 20 possible DRL channels in the pertinent lower or upper DRL band (as appropriate for the TVPU channel to which it is to be associated), and starts transmitting on the first available channel, may be practical."
The two 500 KHz DRL bands at each end of the 2 GHz BAS band will allow broadcasters to implement new features to make digital ENG operation easier and more reliable. For example, a DRL could be used to transmit bit error rate and signal strength data from the ENG receive site to the ENG truck. This data would let truck operators know when the signal was getting close to the threshold. Unlike analog, a digital signal doesn't degrade gracefully. Another application is to use the DRL to aim the dish on the ENG truck and adjust transmitter power automatically. Automatic transmitter power control would help minimize interference while maintaining enough margin for reliable reception under varying conditions.
The FCC Orders dropped Phase 1 of the BAS reallocation plan, going directly to Phase II. See the TV Technology Newsbytes article FCC Revises BAS Reallocation Order for more details on the new reallocation plan and schedule. Refer to the Third Report and Order and Memorandum Opinion and Order for tables showing the new channel plan and more details on the reallocation process.
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