The high-efficiency broadband antenna, or HEBA, is an omnidirectional AM broadcast antenna that has been described as immune to seasonal variations in ground conductivity. Its footprint also is significantly smaller than a traditional antenna, because it does not require ground radials.
According to Worldwide Antenna Systems, the developer, these characteristics have sparked considerable interest within the AM broadcast industry.
In September, the FCC granted nighttime approval for HEBA operation on 940 WQVR(AM) in Webster, Mass. Engineer David Maxson was part of the process to gain that approval. He will present a session at the NAB Show titled “Proving the HEBA Antenna,” Monday April 7, in the Broadcast Engineering and IT Conference.
Maxson will discuss the design, measurement techniques and insights from NEC-5 software modelling. Grady Moates of Loud and Clean Broadcast Science, part of WQVR’s engineering team, and consulting engineer Peter Zollman assisted Maxson with preparing the paper associated with his talk.
Maxson has worked as a broadcast engineering consultant since 1982, when he co-founded Broadcast Signal Lab, the precursor to his present business, Isotrope, which launched in 2010. His contributions include NAB presentations on measurement and interference issues and helping to standardize HD Radio broadcasting, including authoring “The IBOC Handbook — Understanding HD Radio Technology.”
Addressing efficiency
The HEBA’s architecture has raised questions within the industry: What are its underlying physics? How efficient is it, exactly?
In the WQVR deployment, the HEBA stands 72 feet high and occupies a 40-foot-square footprint. It has two driven elements: a cylindrical horn-shaped vertical frame positioned above and a large capacitive plate parallel to the ground plane below it.
Maxson said the HEBA form factor is based on the Crossed-Field Antenna, a reference that may spark memories among engineers.
In the paper, submitted for the NAB Show BEITC Proceedings, he noted that while the two antennas share similar physical components, they are optimized differently.
“The CFA was designed around the controversial premise that ‘independent’ magnetic and electric fields could be ‘crossed’ to produce a propagating electromagnetic wave,” Maxson wrote. While the HEBA evolved from the CFA’s architecture, he said it is based on more “pragmatic” broadcast engineering principles.
“The HEBA’s shape and method of excitation were not analogous to regular towers,” Maxson said, “and these features naturally fostered skepticism during the FCC approval process.”
It was uncertain whether the standard FCC equation for predicting tower performance could model the HEBA’s vertical pattern accurately.
This led to a decade-long process to gain both daytime and nighttime operation approval from the FCC.
Background
Initial experimentation with the HEBA began in 2011 on a small wooden platform with an arrangement of elements built at the tower site of WQVR (formerly WGFP).
After preliminary testing and development, the FCC granted an application for experimental operation in 2015. When tests at a higher frequency proved successful, Maxson said the design was scaled to operate at the station’s frequency, 940 kHz.
By mid-2016, a new, larger antenna was constructed from the ground up at its current location near the transmitter building. Final testing was completed in 2017 and the station secured a license for daytime operation in 2018.
Efforts to evaluate the HEBA’s vertical pattern encountered several procedural dead ends until NEC-5 modelling software revived the project in 2022, leading to final FCC nighttime approval in 2024. The station’s nighttime power remained limited to 4 watts to protect a co-channel 50 kW clear-channel station in nearby Montreal, Canada, from skywave interference at the Canadian border.
“Regardless of the final nighttime power authorization, proving the vertical pattern to the FCC required a rigorous process,” Maxson said.
Modelling for the future
Maxson said he will discuss some of the findings from the NEC-5 modelling. He will also address the antenna’s ability to set up a radiating signal without being overly coupled to and dependent on the earth ground near it.
He is optimistic regarding the antenna’s performance.
“Its features offer benefits not seen with other short AM broadcast antennas. The dual-feed arrangement appears to enhance the electrical height as well as cooperate with the elevated ground plane to reduce near-field ground losses.”
He said future HEBA deployments will need to be modelled separately for running on different frequencies. But as the designs evolve, he believes, “It will come to a point that the HEBA can be standardized and authorized by calculation without modelling each design.”
With its reduced height and smaller footprint not dependent on a grounding system, Worldwide Antenna Systems says, the HEBA could be a way for AM stations to monetize their current tower real estate.
