06.23.2006 12:00 AM
Broadcasters Press for White Space Revisions
Legislation in the Senate telecom package opening unused broadcast channels up for unlicensed devices enjoys wide support on the Commerce Committee, but broadcast reps say it still needs work. The bill would allow operation of unlicensed and uncoordinated radio frequency devices in the permanent core DTV channels 2-51. David Donovan, head of the Association for Maximum Service TV, said doing so would wreak havoc with digital TV receivers.

In a June 21 letter to committee co-chairmen Ted Stevens (R-Alaska) and Daniel Inouye (D-Hawaii), Donovan said the legislation "will have the unintended consequence of creating significant interference to digital television receivers... As a matter of physics, any device transmitting energy in the TV band has the potential to interfere with both digital television sets and government subsidized digital-to-analog converter boxes."

Indeed, Charles Rhodes, a preeminent broadcast engineer, has published empirical evidence of DTV signal interference in his column in TV Technology magazine. Rhodes demonstrates that the energy of various transmissions doesn't necessarily stay within the constraints of a given swatch of spectrum as if it had pipe walls, but rather bleeds into adjacent channels.

In his letter to the senators, Donovan cited the current interference problem from RF devices certified by the FCC, but later found to be noncompliant and transmitting at power levels much higher than those authorized. The National Association of Broadcasters tested several such devices and sent its results to the co-chairmen and to FCC Chairman Kevin Martin. Of 17 wireless FM modulators on the market used to transmit MP3, iPOD or satellite radio through an in-dash car radio, 13 exceeded the FCC's allowable field strength; six by 2,000 percent, and one by 20,000 percent. Many were also "wider in bandwidth than permitted by the FCC, resulting in potential interference to first and second adjacent channels as well," the NAB said.

Donovan pointed out that there are already millions of these FM demodulators in the hands of consumers, with no means for recalling them or turning them off. He said that this situation foreshadows what will happen in the DTV realm if the current bill becomes law.

Donovan enumerated failings of Senate bill and called for changes in the following areas:
• Consumers are not eligible to file interference complaints, even though their television reception is suffering from interference.
• An impossible burden will be placed on incumbent licensees in terms of verifying complaints generated by the unlicensed devices.
• There is no requirement for device identification codes, which would make it easier to track down offending devices.
• There is no provision for remote shut off capability in the devices, which would make it easy to disable an offending device.
• No provision is made to bar devices from operating on first adjacent television channels.

In his plea for changes, Donovan said that broadcasters had spent billions of dollars in converting to digital broadcasting and that customers would be spending tens of billions for new receivers.

"This federally mandated investment must be protected from interference from unproven unlicensed technology and should not be jeopardized so that a few large companies can sell chips to be used in games and toys," Donovan said.


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