Foti: Informal Feedback Shows FM SSBSC Reduced Multipath

Some initial tests completed, more are planned by NPR Labs
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Frank Foti addresses the IEEE Broadcast Symposium audience. Photo by James O'Neal.

Frank Foti of Telos/Omnia says NPR Labs has completed some testing of his FM modulation scheme and more tests are planned.

The FM stereo technology is called single sideband suppressed carrier modulation. The goal is to reduce FM multipath, not eliminate it, he told attendees at the IEEE meeting in Alexandria, Virginia today.

FM SSBSC is compatible with existing modulation monitors and receivers, but he wanted to determine if using it would degrade existing analog service. NPR Labs has done some lab testing using a multipath simulator. “They’ve come up with multipath profiles done on a predetermined time period,” with a profile meaning a travelled route in this case, according to Foti.

NPR Labs conducted repeatable tests using different receivers and different RF levels. “After a day of testing we came away with the feeling there were some differences” between single sideband and double sideband transmission, “but one was not better than the other,” said Foti.

With single sideband transmission, there’s going to be multipath. “While there has been concern that using FM SSBSC would cause more multipath, we think no,” he said.

For his field testing on a low power frequency, 87.7 MHz in Cleveland, Foti used the same audio content and same route and speed, comparing double sideband and then single sideband transmission. There were “some annoyances” with the single sideband transmission scheme but not as intense and long as with the double sideband version, he said.

The informal feedback so far shows multipath has been reduced, using FM SSBSC, according to Foti.

What is the overall goal of the FM SSBSC? “Can we do something in today’s broadcast infrastructure to improve FM stereo signal that would benefit the listener,” according to Foti who noted that both his company and Orban offer the feature. FM SSBSC is on the air in numerous markets with experimental authorization, he noted.

More testing is ahead. Telos/Omnia and NPR Labs are working out a test proposal. The NRSC has a working task group on this, as we’ve reported.