As far back as the early 20th Century, people have been listening to the radio to get the latest news, listen to music and hear their favourite radio programmes. It was, in short, the entertainment and information medium for the masses.

In the early 21st Century, radio is ubiqitous, and still popular despite the growth of CDs and digital music. Compared to these, the drawbacks of radio have become more and more apparent. Analogue radio is fuzzy and static fills the car when driving under bridges or through tunnels. When driving long distances, particularly in countries larger than the UK, the radio will need to be retuned to a different station if you want to keep listening. The content is limited to music, sports and talk radio, much of which must be monitored to make it appropriate for all ages.

While in Europe, Digital Audio Broadcasting (DAB) is becoming more popular, an alternative for North Americans is Satellite Radio, or SDARS - Satellite Digital Audio Radio Service.

Compared to analogue, this is a new way to listen. Clear, uncensored, almost uninterrupted channels spanning everything from music to news, sports, comedy, entertainment and even the weather. The two main providers, Sirius and XM, have almost 200 channels each, so there's something for everyone. The whole of the mainland United States is covered, with coverage even available in Canada and Mexico.

How Does it Work?

There are differences between setting up a traditional radio, and setting up a satellite radio. A traditional radio, and even a DAB radio, is an out-of-the-box ready device. Just plug it in to the mains and extend the aerial, and it's ready.

Satellite radio, on the other hand, is very different. In order to start listening, a subscription needs to be set up with a satellite radio provider; usually this is done via the telephone or the Internet, using a credit card.

Satellite radios are available to fit in-car; many manufacturers in the US offer digital radio as an optional extra, and aftermarket kits are available. In this case, the antenna is located in a 'pod' on the vehicle roof to give the clearest possible view of the sky and the satellites.

For a home satellite radio system, things are done a little differently. The radio receiver also comes with a larger antenna, which has to be positioned correctly. The antenna must have an unobstructed line-of-sight to the satellite, and this will vary depending on which company has been subscribed to and the exact location of the antenna; the company websites contain instructions for doing this, thankfully, as it can be a tricky affair. Once this has been done, listening is possible.

Of course, it is well known that anything that relies on a signal from a satellite can be temperamental. The signal can fade in and out with the passing of the clouds, or it can get choppy when the wind blows a few tree branches in front of the antenna, or when you are driving through a city with tall buildings. While traditional analogue radio isn't as prone to these problems, interference can still be caused by large structures such as building frames which may block or reflect parts of the signal, causing reception problems.

Signal issues aside, the overall sound quality of satellite digital radio is astounding. Most of the time, it can be as good or better than the CD player. The variety of programming available is far superior to that which is offered by traditional radio.

Why Doesn't it Matter Where my Car Antenna Points?

The car antenna is omni-directional, like a GPS antenna¹, and has a dual-arm design; one arm is optimised for satellite signal reception, and the other is optimised for terrestrial repeater signal reception. One main contributor is the fact that the signal is digital; as long as a signal is being recieved which is of sufficient quality that the tuner can recognise the ones and zeroes, the sound quality will remain unchanged, regardless of signal strength.

Technical Background

Back in 1992, the Federal Communications Commission allocated part of the radio spectrum in the S-Band (which is 2.3 GHz) for the broadcasting of Digital Audio Radio Services. XM and Sirius paid over $80million apiece (£46.5million) to broadcast on this piece of the spectrum.

The companies use slightly different methods to broadcast all this satellite radio. XM uses two satellites, dubbed 'Rock' and 'Roll', which orbit the Earth in a geostationary orbit, one at 85 degrees west longitude and the other at 115 degrees west longitude. Sirius uses three satellites, each on an inclined elliptical orbit. Ground stations send the data to the satellites, which then send them as encoded data to people's recievers, where the data will be decoded and turned into music, artist information and song information, of which the latter two are visible on your recievers' screen. In the event that you are driving through a city, where tall buildings can often block the incoming satellite signal, ground-based repeaters will pick up the slack and ensure that you get to hear your music/news/etc.

Worldspace Satellite radio works a bit differently. Currently, they have three satellites in a geostationary orbit, covering the vast majority of Asia, Africa, the Middle East and the United Kingdom. They broadcast roughly 50 channels over the 1,467 - 1,492MHz segment of the L-Band spectrum. While they don't have quite the channel and content selection of XM and Sirius, their ability to cover a larger area of the world puts them ahead in satellite broadcasting.

These companies are funded mainly through subscriber fees and advertising; some revenue comes from various other companies that they have marketing agreements with, such as XM's deal with General Motors to have their radios installed in various makes and models of GM vehicles. Sirius has a similar deal with Ford and its ancillary brands for all cars sold in the US. The majority of the music channels on all three services are commercial-free, so the advertising is done through the talk, news, and entertainment channels.

The range of programming is extensive; Sirius has a show hosted by notorious 'shock jock' Howard Stern, and music channels on all providers range from current chart hits to grunge, hip hop, 1960s, 1970s and non-stop Elvis.

Other Free Options

If subscribing to an advert-free satellite digital radio service isn't a favoured route, the other digital radio option in the United States is IBOC, short for In-Band On-Channel. There are two competing companies. The first is HD, or Hybrid Digital Radio, launched by iBiquity and the second is FMeXtra by Digital Radio Express. Both HD Radio and FMeXtra are broadcast alongside the standard analogue signal, using subcarriers of the existing signals.

HD Radio in particular has a few obstacles to overcome before it can become as widespread as satellite radio. The broadcasting station must modify and upgrade their transmitters before HD Radio signals can be broadcast, and then they also have to pay iBiquity a licensing fee. While FMeXtra doesn't require the degree of equipment upgrading that HD Radio does, at the moment it isn't as popular an option.

Differences Between IBOC and DAB

IBOC uses existing FM frequencies, whereas DAB utilises Band III (174 - 240MHz) and L-Band (1452 - 1492MHz) spectra: the United States military has reserved the L-Band exclusively for military use within the United States. Europe and Canada were part of the Eureka 147 project, which gave birth to the the DAB standard, and Canada has to restrict its DAB broadcasting so as not to interfere with United States military transmissions.

IBOC is very much new technology for the United States; at the moment only 60% of the United States has coverage, and 90% coverage is targeted by 2008. Vehicle manufacturers such as BMW are beginning to offer compatible radios in cars, and IBOC compatible home and portable radios are as available as their satellite equivalents. However, the channels available are only digital variants of AM and FM stations, where those stations have decided to broadcast digital content.