The FM digital radio systems place redundant digital sideband signals above and below a station’s existing analog signal. In the past, the FCC assumed that the power level on each digital sideband was the same. In other words, there is symmetric digital sideband operation. In the past, an FM station that wanted to use asymmetric sideband operation using different power on each digital sideband had to apply to the FCC for an experimental authorization and renew that authorization every year.
The FCC recently ruled that stations need not obtain a specific experimental license to operate a symmetric digital sideband. The FCC noted that “asymmetric sideband operation will allow stations to operate with different power levels on the upper and lower digital sidebands, as a way to facilitate greater digital FM radio coverage without interfering with adjacent-channel FM stations.” The Commission concluded:
“We therefore authorize digital FM stations, except stations operating on Channels 296 - 300, to originate digital transmissions at different power levels on the upper and lower digital sidebands without having to request experimental authorization, consistent with the requirements set forth herein. As further discussed below, a digital FM station need only notify us of asymmetric sideband operation by filing notification on Form 2100, Schedule 335-FM – FM Digital Notification (Schedule 335-FM) in the Bureau’s Licensing and Management System (LMS) database.”
To commence asymmetric service, a station must notify the FCC using Form 335-FM. The FCC has delayed a decision on higher digital power levels pending additional work regarding interference with aviation.
This is a technically complex issue. We suggest you contact your station engineer and communications attorney.
You can access the FCC’s decision here.