Column 19: Internet radio (2011-01-19)

This is one more column after the series about the radio spectrum. This is not about a particular section of the radio spectrum. Indeed, Internet radio does not necessarily involve the use of radio waves at all. Yet it may be the future of radio broadcasting. For the market niches that were traditionally covered by shortwave radio, this future has already begun, as least in Europe and North America. At least, Internet radio is more popular than DRM and DAB (in most countries).

The Internet

The history of the Internet starts in 1969, when the first computers are connected via the very first version of the Internet Protocol. The Internet was originally developed by the US military, so their computers could communicate, even if a large part of the network was damaged.

In the early days, the Internet was intended for text messages (such as mail), file transfer and remote login. Transfer of real-time digital audio was completely out of the question, if only because the data rates were orders of magnitude lower than today. The World Wide Web was not yet invented (though hypertext was). But the Internet Protocol can be used to transfer any type of digital information, even those that were not yet in sight when the protocol was invented. Therefore the Internet can now carry web pages, MSN, telephone calls and of course streaming audio and video.

The most widely used version of the Internet protocol, IPv4, was invented in 1981, almost thirty years ago. Specifications of Internet standards are freely available on the Internet, see The RFC Editor site. Standards documents form a small subset of the RFC documents, a series of documents (there are now around 6000 of them) that started in 1969.

Every device on the Internet (computer, mobile phone or Internet radio) has an IP address. In IPv4 the IP address is only 32 bits in size, so there can be no more than about 4 billion of them. There is not even one IP address for every person on the planet. IPv6 (the next version of the protocol) has address of 128 bits, which means there is an unlimited supply of them.

The central concept behind the Internet is routing. Data is divided into small packets (between 40 and 1500 bytes in size), each of which contains a header. The packet header contains the source and destination IP addresses. When a host (such as a web server) wants to send information to a destination (such as your PC), it transmits one or more packets. However, in most cases the packets are not transmitted directly to the destination, but there is a series of routers between them. The first router is typically located inside the server room of the hosting provider of the web site, the last one is typically the ADSL or cable box in your home. Each router is connected directly to at least two networks. It it receives a packet whose destination address is not its own IP address, it decides where to send the packet next. If the destination host is one one of the directly connected networks, the router sends it directly to the destination, but otherwise it selects one of the other routers it may reach (one that is closer to the destination). A router does not need to know the entire path a packet will travel, but it must make a sensible decision. It would be foolish if a router in Amsterdam sends packets for a destination in Germany along a transatlantic cable to New York.

The routing system can be compared to the (physical) mail delivery infrastructure. Mail dropped in a mail box finds its way through several sorting centers and post offices. If the destination address on the mail is correct, it will be delivered there in a few days in most cases. IP packets will be delivered at their destination in a fraction of a second in most cases. Your cable box or ADSL router can be compared to the local post office and the big routers that send IP traffic across transatlantic cables can be compared to the large mail sorting centers. Like the mail system, the Internet occasionally loses packets or it may deliver them in a different order from which they were sent.

Internet packets can be transported over many different types of physical links. There are non-wireless technologies, such as Ethernet, telephone lines (using old-fashioned modems), TV cable, ADSL and glass fiber. There are wireless technologies such as Wifi, GPRS, UMTS, amateur packet radio and satellite links. A router or host that is connected to one or more networks, needs to know only about the link technology of the networks that it is connected to. It does not need to know about other link technologies, even though the packets may later be transported over these other types of links. The Internet protocol is technology independent.


Until the early 1990s, the Internet was only available to universities and other large institutions. Internet access became available to consumers around 1993. In the 1990s, consumers could only access the Internet via telephone modems with a data rate of 28.8kbps or 56kbps, which is hardly adequate for streaming audio. ISDN was also available and offered a data rate of up to 128kbps, but for that you had to pay twice the normal telephone tariff. In The Netherlands it was impossible to have flat fee telephone access, to you had to pay by the minute for Internet access.

The first Internet radio station appeared in 1994, but very few consumers would have been able to listen to it. In 1996, Real Audio was introduced, a compression protocol for streaming audio. In principle it was possible to receive Real Audio streams via a telephone modem.

Around 2000, broadband Internet became available to consumers, both via ASDL (using the normal copper telephone wires, but at higher frequencies) and via TV cable. At that time it became really feasible for consumers to listen to Internet radio.

Around 2001, the Philips Streamium was introduced, a dedicated device that could play streaming audio. This may be considered one of the first dedicated Internet radios.

Many dedicated Internet radios are now available from many different brands. They can be connected to the Internet either via Wifi (wireless) or via Ethernet, which is now available on most home ADSL or cable routers. They connect to a service provider (such as Reciva to get a well-organized list of stations. so you can select stations by country and by genre. Listening to radio stations with a normal PC often means that each station has its own cheesy Flash player. to play the audio stream Most dedicated Internet radios look like traditional radios (portable radios, stand-alone radios or Hi-fi tuners) and many of them can also receive traditional radio (FM or even DAB).

Nowadays, in 2011, the vast majority of regular radio stations in The Netherlands (and most stations in the Western world) have Internet streams that can be listened to world-wide. Using an Internet radio it is possible to receive more than 10000 radio stations, much more than can be received with any shortwave receiver.

Advantages and Disadvantages

Compared to traditional broadcast radio, Internet radio offers several advantages and disadvantages.




There are several ways a radio station can distribute its programs over the Internet:

Podcasting started to get popular around 2004.Podcasts are not only used by radio stations that normally use streaming audio, but many audio programs are available as podcasts only.

Radio amateurs on the Internet

Broadcast radio is not the only type of radio you can hear on the Internet. Around 2005, the radio amateur club of the University of Twente pioneered the WebSDR software. On the client side this is a Java applet that lets Internet users tune to parts of the shortwave spectrum, typically the amateur bands. On the server side this is a receiver that digitizes one or more large sections of radio spectrum and feeds the digital information to a PC. All users to the WebSDR can tune independently of each other.

In November 2010, the original WebSDR went off-line, because of the radio club was relocated to a room with no way to connect an antenna and no outside windows. Until they manage to route coax through a system of hundreds of meters of ventilation shafts or until they get permission to drill a hole through the outside wall or until they put up the receiver in a remote location, this will be off-line. Fortunately there are similar receivers, see

In addition there are several shortwave receivers available on the Internet, but only one user at a time can tune it. Also some audio streams from scanners (especially of air traffic control) are available. In most countries it would not be legal to make this available though.

So even if you have no antenna, you can still enjoy much of radio. This is really the last weekly column. I will probably put up some additions and updates. I may post other radio related material.

Update 2016-05-10

The Web-SDR returned in 2012 and after several upgrades it can now receive the entire radio spectrum up to 29.16MHz, so we only miss the top past of the 10m band. There are now nearly 150 Web-SDR systems, all around the world, but none of these has a near complete coverage of the HF spectrum. Most can only tune to a selection of amateur bands. Some Web-SDR systems receive (portions of) VHF and UHF amateur bands.