The Radio Data System: FM radio adds features to stay viable, part 1

Broadcast FM radio has extended its user-friendly capabilities through the addition of embedded, backward-compatible functionality which adds text and even graphics to the radio display.

From the late 1920s and for decades afterward, AM-based broadcast radio was the primary real-time mass media in the US and the world. In the AM band (550 kHz to 1600 kHz) top-tier broadcast stations pumped out 50,000 watts with signals that could be heard thousands of miles at night at night (due to prorogation effects). Families would sit around the console radio in the living room and listen attentively (Figure 1).

Figure 1. In the “golden age of radio” of the 1930s and 1940s, before the advent of TV in the 1950s, gathering around the tube-based console radio at home to listen to various programs was a common activity (Image: RW Networks Inc.).

Tube-based radios also were installed in cars when Galvin Manufacturing Corp. introduced the Motorola radio in 1930, one of the first commercially successful car radios. Company founder Paul V. Galvin created the brand “Motorola” for the car radio by linking “motor” (for motorcar) with “ola” (which implied sound). Within a few years, AM radios were common features in cars, as they brought music, news, bulletins, and general connectivity to people in cars (remember, if you were in a car in those days, you were effectively “cut off” from the outside world).

In the 1950s and 1960s, FM radio became a factor with its better sound and noise immunity. It was invented almost singlehandedly by Maj. E.H. Armstrong, an engineering genius who had previously developed the super-regenerative receiver and its superior successor, the superheterodyne receiver architecture. With the development of transistors in the 1960s and 1970s, portable AM and AM/FM radios became standard consumer must-have products.

The radio world has changed
Flash forward to the 21st century, and broadcast radio no longer has a dominant position. In fact, its share of user “mind” and influence is greatly diminished; market research numbers (mostly sponsored by radio associations) tend to paint a brighter, upbeat picture, with uplifting statistics (“82 million Americans listen to AM Radio Each Month”) but the harsh reality is undeniable: with alternatives such as the Internet, streaming music services, podcasts, downloadable music, satellite-based radio (Sirius/XM) and more, radio’s role and impact are far from what it used to be.

AM radio is having a much harder time than FM radio. Nielsen and other surveys still boast about the reach of AM radio – most of it while in the car – without saying how attentively people actually “listen” to it. The entire AM radio/car situation got a lot of attention recently when Ford Motor announced that it would be dropping AM radio from its upcoming electric vehicles (EVs), which they acknowledged was largely due to challenging issues of EMI/RFI in the radio band due to the electrical noise from switching electronics.

Note that Ford is not the first to drop (or try to drop) AM radio, as other vendors such as Telsa already have done so. Columnists and pundits across the spectrum had a great topic to cover. (Later, under pressure from legislators and others, Ford reversed that decision.)

The AM broadcasters saw this trend years ago and tried to hold off the wave of alternatives. First came DAB – Digital Audio Broadcasting – which “piggybacked” digital encoding of the radio signal itself onto available subchannels of the AM band to provide better audio quality (one of the inherent drawbacks of AM) but it never really caught on. Among the many presumed reasons for low acceptance is that it requires an entirely new and more costly receiver and is harder to use – a big challenge for consumer products of this type.

FM radio tries a different approach
The FM broadcasters have also tried to maintain their viability by adding a feature that newer FM radios could use: the Radio Data System (RDS). It first appeared in Europe in the 1980s and soon was adopted with a slightly different name and some minor differences in North America, called Radio Broadcast Data System (RBDS). It even got a branded logo, analogous to Wi-Fi, to highlight the feature (Figure 2).

Figure 2. The Radio Data System (RDS) has its own logo, following the branding idea of Wi-Fi (Image: Science Direct).

RDS adds only a small cost to the FM radio, especially as it is primarily a decoding function at the receiver and modern FM ICs can implement to the needed capability. Unlike DAB, RDBS/RDS does not change the basic FM modulation scheme, but it does add some user-helpful features while maintaining compatibility with the millions of FM receivers in use and being invisible to them – which is a very good thing.

This FAQ will look at how RDS (and the very similar RBDS) works, what it can do, and its present status. It is instructive to first look at some FM radio “upgrades” of the past to establish context for the RDS approach. The next part looks at the broader issue of maintaining receiver compatibility as new features are added.