Philipp Schmid, Chief Technology Officer, Nautel spoke about Increasing Spectral Efficiency for VHF Band II by Transmitter Combining FM Digital Radio Signals on the second day of ABU DBS 2021.
The session was chaired by Steve Ahern, Head of ABU Media Academy.
Schmid has earned multiple patents during his tenure with Nautel. He was recognized in 2017 by the National Association of Broadcasters for “best paper” at the BEITC (Broadcast Engineering and Information Technology Conference). Recent projects have included research and testing of all-digital AM (DRM & HD Radio); extended HD Radio FM service modes; Nautel HD Multiplex™, with up to 15 HD channels on one transmitter; and the development of IP STL technologies for HD Radio.
He began the session by identifying the problem of having many FM bands being full in many big markets, so it’s not possible to add high power analog channels in existing FM band. It’s expensive to add many new analog transmitters and difficult to build out nationwide audio networks.
The solution is to achieve multi-channel audio services by unlocking new digital channels using the in-band standards of HD Radio or DRM. Digital allows 400kHz interleaving of analog and digital stations and digital signals can be combined in single transmitter for efficient broadcast of 12 to 18 audio services.
HD Radio can produce up to 1 analog and 4 audio services using 10 percent of the power of analog FM while pure DRM uses all of the power and can carry up to 3 audio services.
Using just digital services, we can now create a larger multiplex of systems, which can co-exist with exiting FM band. For this one needs to look at the FM protection rations employed to govern FM allocations in various countries.
With a 400 kHz spacing between stations, one can add more power to the transmission site but the adjacent channels may already be allocated. HD Radio however, places sidebands at 150 kHz on either side of the FM carrier offset at 10% to 12% total FM power, providing comparable coverage. With DRM, there is only one sideband at 10% of the power.
Since digital transmission needs only 10% of the power, it is interfering less with other stations to achieve the same coverage. If you don’t have any adjacent stations, self-interference from the site is the only limit, which means you can give it a lot more power. If you do have adjacent stations, power will need to be reduced.
Nautel has designed a new digital modulator/exciter that combines multiple IQ modulators that produce their own respective digital signal, which don’t interfere with one another. Philip also discussed results from success demonstrations conducted by the company in Jaipur and Delhi in India.
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