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Radio Thrives in Digital Age

Both Legacy FM Radio and Emerging Services Demand an Increasingly Broad Palette of RF Solutions

Three key factors underpin the long history and bright future of radio broadcasting: a robust business model, relatively simple technology and overall cost-effectiveness.

Over the past century, broadcast radio has evolved into the most ubiquitous medium of the broadcast world.

Heard in almost every household, street corner and village around the world, broadcast radio continues to be a vital and fast-growing sector.

(click thumbnail)Mick BennettCore objective

Even pitted against a growing field of highly competitive alternative media, the “bullet-proof” broadcast radio business model has analysts predicting that legacy analog radio has a long future.

Nevertheless, it is widely understood that emerging digital radio variants will sustain and shape the future of radio over the next decade.

Around the world, the commercial radio broadcasting market is renowned for its fiercely competitive nature and the core objective of broadcasters to establish and retain market share.

FM radio — the most refined analog offering — tends to be regionally localized, leaving openings for more radio broadcasters to join the market.

As a result, the industry is experiencing dual pressures — one from new broadcasters wanting to join the market, the other from incumbent broadcasters looking to expand their services and thus hold on to market share.

Both require spectrum and broadcast infrastructure in an increasingly congested climate.

Spectral squeeze

This “spectrum squeeze” in the FM radio world has inspired a wide range of innovative RF broadcast solutions.

Traditionally, FM is broadcast in part of the VHF band II as 200 kHz channels with 800 kHz spacing.

Spectral squeeze is now behind a rising trend to shrink this channel spacing to 600 kHz and address any resultant receiver interference risks with sharper filtering options.

Where two-pole filters may have once sufficed, more sophisticated three- and four-pole filters are fast becoming the FM norm.

Similarly, the rollout of new FM services demands more space on increasingly congested broadcast towers. This demands a broader range of FM broadcast antennas, featuring innovative radiation patterns, bandwidths, mounting options and physical compactness.

This diversity of need is the defining aspect of 21st century FM radio broadcast systems, which vary widely from site to site and from broadcaster to broadcaster.

Technical challenges

The transition to digital radio is now well established in many parts of the world, most notably in the United Kingdom, the United States, Denmark, Norway and Switzerland.

The reasons for the push to digital radio are similar to those behind the digital television transition — spectral and commercial efficiency; enhanced services to complement traditional audio, such as text, images and listener interactivity and improved quality.

In many respects, the choice of digital radio platforms comes down to national and regional availability of spectrum, specifically that in the VHF band III, L or S bands.

In the case of the more popular DAB/DAB+ platform, the major challenges include spectrum availability; addressing deployment models — conventional “broadcast” models vs. the “cell-style” topologies typically required in L band deployments — and the availability of receivers.

Arguably one of the most pressing technical challenges with DAB/DAB+ is addressing issues of RF filtering, power handling and voltage peaks.

The power of a DAB/DAB+ service can be as high as 10 kW — of the same scale as a DTV service — yet it is squeezed into a narrow 1.5 MHz channel. This exacerbates the digital service peak-voltage challenge, and also presents filtering and power-handling challenges.

Filter response

To meet these challenges, companies such as Radio Frequency Systems (RFS) are exploring solutions such as double cross-coupled filters, filters with not one but two cross-couplings. These achieve much sharper filter response in a fraction of the footprint of a conventional filter, along with a reduction in in-band insertion loss.

Also promising are technologies such as advanced water-cooled filters, in development at RFS. The first of their kind in the world, these filters specifically address the uniquely high power-to-channel bandwidth ratio of digital radio.

Digital radio antenna systems are also evolving and include a range of L band panels and VHF band III antenna solutions that help legacy FM and emerging digital services coexist on a single broadcast system.

In the future, challenges will stem from the evolving global “transmission mask” specifications for digital radio, most specifically, their interpretation and translation into practical network effective radiated power (ERP) levels and filtering solutions.

Though different generations, legacy FM radio and emerging digital radio services have much in common. Both will support the powerful and growing radio business model for some time to come.

For their survival and growth, both demand an increasingly broad palette of RF solutions, a rich mix of antennas, filters, combiners, feeders, patch panels and so on.

Flexibility and scalability, along with a complete end-to-end understanding of the radio broadcast system as a whole, are and will continue to be essential.

Mick Bennett is global product manager, Broadcast and Defense Systems for Radio Frequency Systems (RFS).