Skip to main content

Spectrum Threats Persist

As the demand for spectrum for new services increases, spectrum used by broadcasters is being considered for sharing by both licensed and unlicensed services. The threats in 2004 are similar to those in 2003, except that this year many of the potential threats became more real

The FCC approved rules allowing Broadband Over Power Line, which can interfere with reception of shortwave broadcasts, VHF channels 2-5 and possibly higher TV channels if harmonics are present. The rules include procedures for protecting licensed users sharing the 2 to 80 MHz spectrum with BPL operators, but they are more suitable for protecting two-way radio users in the public safety, aeronautical and amateur radio services than consumers listening to the BBC on shortwave or watching channel 2 on TV. There are concerns these rules may not be enough. Experimental BPL facilities have been allowed to continue operation even after amateur radio operators have demonstrated interference from the system. Will the FCC rules and the BPL industry's methods for eliminating interference be effective in eliminating real-world interference to broadcast reception?

The FCC proposed rules for sharing unused TV channels with unlicensed devices, both low power portable devices and higher-powered fixed links. The National Association of Broadcasters and the Association for Maximum Service Television have opposed this. We'll have to wait until 2005 to see if their concerns are addressed and, if unlicensed devices are allowed to share the spectrum, how they will be regulated.

Elsewhere I discussed how 2 GHz broadcast ENG was transitioning to digital to free up 34 MHz of spectrum for other services. This year the FCC adopted rules allow Department of Defense (DoD) satellite uplinks to share the remaining 2 GHz ENG band with broadcasters, in spite of opposition by the Society of Broadcast Engineers (SBE) showing such operation would cause large amounts of interference to TV ENG near the uplinks. In one filing, SBE showed that all the ENG sites in Denver would have line of site to the DoD uplink location. While the uplinks aren't expected to be operational in 2005, the debate over their interference potential is likely to continue.

Interference concerns weren't limited to broadcast spectrum. Several C-band satellite users opposed FCC rules allowing Ultra Wideband (UWB) systems to operate in the 3.7 to 4.2 GHz C-band downlink band. The Satellite Industry Association (SIA) and Coalition of C-band constituents submitted comments and studies showing widespread use of UWB would cause serious interference to C-band downlinks. The FCC, however, in their analysis of the study said the assumptions on which the study was based were unrealistic. The FCC concluded that if its own, more realistic assumptions were used, interference was unlikely. The FCC said if there was interference, users of the UWB devices would have to modify their operation to eliminate the interference. As UWB technology use becomes more common, we'll see if the concerns of the SIA and the Coalition were realistic.

I believe the big interference story in 2005 won't be BPL or unlicensed devices, but interference between TV stations as stations increase DTV power to meet the July 2005 and July 2006 deadlines. I'm sure Charlie Rhodes and I will be spending more time discussing that in 2005!