TETRA systems will not be permitted to operate on National Public Safety Planning Advisory Committee (NPSPAC) frequencies in the 800 MHz and 700 MHz bands, according to an FCC order released yesterday that cites potential interference if TETRA was deployed on these airwaves.

“In this Report and Order, we adopt rules that guard against interference to critical public safety communications in the 800 MHz National Public Safety Planning Advisory Committee (NPSPAC) Federal Communications Commission FCC 16-48 2 band1 (806-809/851-854 MHz) by confirming the emission mask applicable to digital transmissions in the NPSPAC band,” the FCC order states.

“In so doing, we lessen the possibility that first responders will encounter harmful interference in the NPSPAC band and provide certainty to manufacturers concerning the capabilities required of radios used for interoperable communications.”

Although the FCC order focuses primarily on 800 MHz public-safety spectrum, a footnote in the order also addresses the public-safety 700 MHz narrowband airwaves.

“The Commission also declined to permit TETRA on the narrowband portion of the 700 MHz public safety band, noting that TETRA does not conform to the interoperability standard for the 700 MHz narrowband public safety band interoperability channels,” the FCC order states.

TETRA is the dominant public-safety LMR technology in many parts of the world, including Europe. But Project 25 (P25) as the primary interoperable standard in the United States and conforms to Emission Mask H to limit adjacent-channel interference.

The FCC has allowed TETRA to be deployed in the U.S. on spectrum that is not dedicated for public-safety use, but there has been some debate in recent years whether TETRA could be deployed on public-safety spectrum.

TETRA manufacturer PowerTrunk—now owned by the Sepura Group—has been the biggest proponent of TETRA being allowed for use on public-safety narrowband spectrum. PowerTrunk’s low-power TETRA technology conforms only to Emission Mask B, which was allowed by FCC rule for analog transmitters equipped with an audio low-pass filter.

Although the FCC acknowledged that its previous rulings had created some ambiguity in the industry about what technologies are allowed on public-safety spectrum, yesterday’s order is designed to close this “loophole” and bring greater certainty to the market, the order states.

PowerTrunk stated in FCC filings that the TETRA emission mask would create a greater potential for interference with surrounding systems, but the company asserted that regional planning committees (RPCs) could address this. In addition, the company claimed that TETRA’s greater spectral efficiency in delivering data would offset any interference disadvantages.

But the FCC disagreed with the PowerTrunk argument, claiming that other LMR technologies offer similar data throughput without the interference risk of low-power TETRA.

“It is inescapable that PowerTrunk’s equipment—which conforms only to Emission Mask B—has a greater potential for adjacent-channel interference than equipment that conforms to Emission Mask H and analog signals subject to audio low-pass filtering,” the FCC order states. “Therefore, to accommodate a low-power TETRA system such as PowerTrunk’s, the RPCs would be required to increase geographic separation, thereby limiting the use of available spectrum in the NPSPAC band, which already is congested in large metropolitan areas.”