NAB President-CEO David K. Rehr sent a letter Tuesday to every U.S. congressional office warning that a campaign by several technology companies to win regulatory approval to sell unlicensed personal-portable devices poses a serious threat to a successful digital television transition.

"For more than a year, these companies have tried to convince the Federal Communications Commission and members of Congress that they can make devices that will not cause interference to broadcasters, wireless microphone users and other parties that currently use this spectrum," Rehr wrote. "Unfortunately, based upon the results of FCC testing to date, their technical prowess does not match their rhetoric."

Noting that prototype devices tested by the FCC have failed testing on at least three occasions, Rehr cited the technology companies' continued public relations campaign, which he said was "designed to convince members of Congress and the FCC that their engineering failures should not be the focus of attention."

"They would rather you focus on the unrealized benefits of these theoretical, unproven devices rather than the legitimate interference these devices cause to televisions and wireless microphones," Rehr said.

Rehr reminded lawmakers that broadcasters are a vital lifeline serving as an essential informant during times of crisis, and he cited NAB's support for promoting broadband deployment in rural areas.

He also noted that broadcasters are not alone in expressing concerns over interference, citing a recent FCC filing submitted by The Sports Technology Alliance, a group that includes Major League Baseball, NASCAR, the National Basketball Association, the National Collegiate Athletic Association, the National Football League, the PGA Tour and ESPN. Religious organizations, Broadway theater groups, wireless microphone manufacturers and healthcare organizations have also expressed concern regarding the interference-causing technology.

One version of the letter, sent to every congressional office, is available here.