Radio Topics

AM Carrier Power Reduction in All-Digital Service Mode MA3 - $15

Some AM radio stations have turned off their analog broadcasts and converted to digital-only operations, with the possibility of better coverage, improved ratings, and more competitive features. Since a modulated analog signal is not present, it is possible to reduce the main carrier power in All-Digital service mode MA3 without adversely affecting audio quality and availability. This might not only decrease conversion costs but could also save broadcasters thousands of dollars per year in utility bills. Alternatively, the resulting power savings could be applied to the digital subcarriers, thereby enhancing the robustness of the digital signal.

Since receivers use the main carrier to demodulate the digital signal, reducing its power could potentially degrade reception performance. Specifically, HD Radio receivers use the main carrier to correct frequency differences between the received and transmitted signals, and to normalize the amplitude of the digital subcarriers across the allocated channel bandwidth. Xperi has analyzed and simulated the effects of reduced main carrier power to determine an acceptable decrease and quantify the resulting degradation. Results indicate that a 6-dB carrier power reduction, with a concomitant 4-dB reduction of the two OFDM reference subcarriers, should have a negligible impact on signal robustness.

The next logical step in assessing the viability of reduced MA3 carrier power was to validate these predictions by measuring performance in a real-world automotive environment, using Hubbard Broadcasting station WWFD in Frederick, MD. Field tests were performed over multiple routes to expose the signal to a variety of terrain, speed, interference, and shadowing conditions.

This paper will review Xperi’s analytical and simulated performance predictions and will present field test results that successfully validate them. Results indicate that reducing carrier power by 6 dB and reference subcarrier power by 4 dB has an insignificant effect on WWFD’s MA3 digital audio coverage area.

Paul Peyla | Xperi Inc. | Columbia, Md., United States
Jeff Baird | Xperi Inc. | Columbia, Md., United States
Dave Kolesar | Hubbard Broadcasting | Washington, D.C., United States

Drone Measurements Validate the Accuracy of Simulation for FM Pattern Verification  - $15

An extensive amount of experience has been gained in both drone measurement techniques of television broadcast antennas and data analysis using electromagnetic simulation. Through comparison, drone measurements and simulation predictions have time and time again validated that the techniques provide accurate measurements and predictions at UHF and VHF frequencies. Now that the FCC television channel Repack has passed, extending what has been learned to the FM market will provide new opportunities for FM broadcasters. Understanding the limitations of “old school” FM pattern range measurements and the power of computer simulation will be discussed in this paper. It will also include case studies, one of which would be impractical for any far field range and can only be realized using simulation and validation using drone-based measurements.

John Schadler | Dielectric LLC | Raymond, Maine, United States
Jason Schreiber | Sixarms | Gold Coast, Australia

The Hierarchy of Latency  - $15

“Low Latency” is an overused term and hides important technology design concerns and constraints. To bring clarity to the design of modern digital audio, audio networks, and cloud computing, this paper defines and describes multiple aspects of the meaning of latency in the context of modern audio production, with example numerical values. A one-page chart is presented, visualizing the range and meaning of the Hierarch of Latency.

Greg Shay | The Telos Alliance | Cleveland, Ohio, United States

Understanding Digital FM Asymmetric Operation - $15

The FCC is considering a rule change that will make it easier for FM-band HD Radio™ broadcasters to operate with asymmetric digital sidebands. Doing so gives broadcasters the opportunity to increase digital power on one sideband only, providing improved coverage while mitigating interference to adjacent-channel stations. This paper includes background information on asymmetric sideband operation, and its application to broadcast stations. A shift to asymmetric power levels will require broadcast engineers to change how they describe and employ digital sideband levels on a station.

Alan Jurison | iHeartMedia | Syracuse, N.Y., United States