Column 3: Mediumwave broadcast band (530-1611kHz, 2010-09-29)

Covering wavelengths 185-566m, the mediumwave broadcast band is used worldwide. Almost every country in the world has some stations there. It has been in use as the primary radio broadcasting band since the early 1920s. In the USA it was often called the Broadcast Band, until FM radio gained popularity. At that time, mediumwave became known as the AM band.

Band diagram 530-1611kHz

As everyone knows, the mediumwave band opens up at night. During the day only a few strong nearby stations can be heard. at night the band is chock full of stations. In The Netherlands this means full of stations from all over Europe, in the USA it means full of stations from all over the USA. This make it a fascinating band to listen to.


When the first radio broadcasts started around 1920, there was no clear concept of a broadcast band. At that time all radio transmissions took place at wavelengths above 200m (and frequencies below 1500kHz). Most broadcasters were allocated frequencies above 500kHz, but in Europe, some stations were allocated frequencies below 500kHz and a longwave broadcast band was formed there. Apparently this did not happen in America, possibly because the authorities wanted to reserve those frequencies (with better groundwave propagation) for professional users only. 500kHz was already established as the international distress frequency, so no broadcast stations transmitted exactly at this frequency. So all broadcasting stations in America and many in Europe happened to transmit in the part of the spectrum that we now call the mediumwave broadcast band, right from the very beginning.

Both the Dutch station PCGG (operated by Idzerda between 1919 and 1924) and the American station KDKA (starting 1920) started their services in order to sell broadcast receivers to the public. In America, most broadcasters were commercial and financed their transmissions with advertising. In Europe, however, most countries established public broadcasting stations. In some countries they were run by a government organization, but mostly they were run by nonprofit organizations (like the BBC in Great Britain). The Netherlands was unique in the sense that multiple competing nonprofit organizations got a license to broadcast. Most European countries had a mandatory license fee that you had to pay if you owned a radio. In The Netherlands this mandatory fee was only introduced in 1940. Before that, broadcasters were mainly financed by voluntary membership fees.

Five of the public broadcasters that we know today in The Netherlands were founded in the second half of the 1920s. They were KRO (Roman Catholics), NCRV (Protestant Christians), VPRO (Liberal Protestants), VARA (Labour, social-democrats) and AVRO (general, non-religious). Apart from that, a protestant church in Bloemendaal got a license to broadcast (locally, low power) in 1924. This mediumwave station still exists today and it can be heard every Sunday at 1116kHz.

In 1928 the BBC in England experimented with television on mediumwave. This is what we call narrow-band television, 30 scan lines and 10 frames per second. This signal had an audio-frequency bandwidth of less than 10kHz and it could be transmitted on mediumwave. Apparently the resolution was enough to recognize human faces when they were full screen. It's hard to imagine watching a movie at this resolution though. The television receiver contained a Nipkov disk, a fast-spinning disk with tiny holes in it. A neon lamp was modulated with the received video signal and was visible through one of the holes. Because the disk spun fast enough, you could see a complete moving picture through a small square window. The camera contained a similar device with a photocell instead of a neon lamp. The disks in both machines had to spin synchronously and in the first television sets this synchronization has to be performed manually. Needless to say, this system was for the (wealthy) diehard geeks only.

In the USA, frequencies of AM stations started to be exact multiples of 10kHz very early on, so a channel spacing of 10kHz may have been in effect since the 1920s, as it remains today. In Europe and other regions of the world the situation was very different. Band plans were already made in the late 1920s, but there was no uniform channel spacing. Since 1950 (after the Copenhagen plan of 1948 went into effect), the mediumwave had a channel spacing of 9kHz, but carrier frequencies were 1kHz less than an even multiple of 9kHz (so there was a channel at 899kHz instead of 900kHz). A small section of the top of the mediumwave band used 8kHz channel spacing. In 1977 the mediumwave in Europe moved to a uniform 9kHz channel spacing were all channels were at an exact multiple of 9kHz. Existing stations moved 1kHz up. The Dutch stations formerly on 675, 746 and 1007kHz, went to 675, 747 and 1008kHz. All of ITU regions 1 and 3 now use this channel spacing, while ITU region 2 uses 10kHz spacing.

It is very important to use channels in the mediumwave band. If you receive two stations at once, they are either at exactly the same frequency or 9kHz or 10kHz apart. In the former case you hear the audio of two stations mixed together. In the latter case a good IF filter can separate the two signals. Now suppose there are two stations 1kHz apart. Now you will hear a beat note of 1kHz, usually making both stations unlistenable. This is much more annoying than hearing the faint audio signal of another station through the program that you want to listen.

In the old days, radios had analog tuning, so you could tune to each and every frequency within the mediumwave band. A radio for the American market could be used in Europe without problems and the other way around (apart from different mains voltages that is). Today most mediumwave radios can only be tuned to the exact frequencies of the mediumwave channels, so you cannot tune to 675kHz on an American car radio. World receivers can often be switched between 9kHz and 10kHz channels and they can be finetuned (1kHz steps) between two channels.

In Europe the mediumwave band runs officially from 526.5 to 1606.5kHz with 120 channels from 531 to 1602kHz. Vatican City is using the next higher channel (1611kHz). In the USA the mediumwave runs from 525 to 1715kHz, with channels from 530 to 1710kHz. The segment between 1600 and 1710kHz was added in the 1990s.

In the USA they used the CONELRAD system between 1951 and 1963. If the enemy would attack, most transmissions would go off the air and a few mediumwave stations would remain to send essential information to the public. Those would only transmit on 640 and 1240kHz, so enemy aircraft would not be able to use AM stations as navigation beacons. Radios were required to have markings on the dial at 640kHz and 1240kHz.


Until 1965, The Netherlands had two public radio stations, both of which could be heard on mediumwave (before World War 2, one of the stations was on longwave). In 1965 a third public station was added, which could also be heard on mediumwave. In 1976 a fourth radio station was added, which transmitted exclusively on FM. Until then, you could hear all Dutch national radio stations on a radio with just mediumwave. The same was true in Belgium and many other European countries. If you had a good quality radio, you could hear all national stations from Belgium, Luxembourg, The Netherlands and Great Britain, plus many stations from Germany and France on longwave or mediumwave. After sunset, stations from all across Europe could be heard. Those were public broadcasters, carrying high quality programming. This was far from hi-fi quality and at times it suffered badly from interference, but still it could be heard most of the time.

Not only legitimate stations could be heard on mediumwave. From 1960 to 1974, the Dutch station Radio Veronica transmitted from a ship in international waters. In 1974 a special treaty came into force and it was now illegal to transmit broadcast programs from international waters. Therefore Veronica ceased its transmissions and eventually it became a legitimate broadcaster. Before that, the station did not really break the law because the radio regulations did not really apply in international waters. Other stations, like Radio Caroline continued to transmit from international waters. Mediumwave pirates in the North Sea (mainly targeting the UK) remained active until around 1990. These days, (land based) pirates sometimes use the band between 1602 and 1700kHz. In The Netherlands these are hobby pirates, not commercial stations.

Because mediumwave signals reach across Europe after sunset, this band is (and was) often used for international broadcasting, just like the shortwave bands. In the 1980s there were very few shortwave stations carrying Dutch language programs. Apart from The Netherlands and Belgium, they were South Africa and the Soviet Union. Radio Moscow regularly transmitted its Dutch language program on mediumwave. Currently Radio Netherlands is using the 1296kHz frequency for some of its broadcasts. On the other hand, mediumwave is sometimes used for local broadcasting using low power transmitters.

Many public broadcasters in Europe have reduced the number of mediumwave stations. Of all Dutch public radio stations only Radio 5 is still active on mediumwave (747kHz). Other strong stations you can hear are BBC world Service (648kHz), Groot Nieuws Radio (religious, 1008kHz) and Radio Maria (also religious, 675kHz). See for listings of mediumwave and longwave stations from all over the world.


The D layer is the lowest layer in the ionosphere at a height between 60 and 90km. It absorbs frequencies below 10MHz (the higher the frequency, the less it absorbs them; signals close to 10MHz are only mildly attenuated, mediumwave frequencies are completely absorbed). The D layer is only present during the day and during the summer it is thicker than in winter. During the day only groundwave propagation is possible. After sunset, the ionized particles quickly recombine and the D layer disappears. At that time, signals can reach the higher layers of the ionosphere and they can be reflected back to earth. Close to sunset and sunrise, the E layer exists and the D layer is not yet formed (sunrise) or has already disappeared (sunset). The signal is then bounced against the E layer. In the middle of the night the E layer disappears as well and signals are reflected against the (higher) F layer. Therefore propagation around sunset and sunrise is different from propagation in the middle of the night. It is possible for the reflected wave (the sky wave) to interfere with the groundwave and this causes fading. A good radio has an effective AGC (Automatic Gain Control) circuit to compensate for that fading.

With good equipment and antennas, transatlantic DX is often possible. Because Europe and America use different channel spacings, it is immediately clear (unless the station is at a multiple of 90kHz) that a station is from the other continent. Under the right conditions, truly worldwide propagation is sometimes possible.


Crystal radios work reasonably well on mediumwave. They are neither sensitive nor selective, but they can pick up the strong local stations. When I was 13 years old (in 1980) I had built a crystal radio with an extra audio amplifier from a Philips experimenter kit. At some time I could get five stations: the three Dutch public stations, a Belgian station and BBC World Service.

In the 1920s the most popular type of radio was a regenerative receiver. It contained a single triode amplifier and a single tuned circuit. The output of the amplifier was fed back into the input, so it would almost, but not quite, oscillate. The feedback regulator had to be precisely tuned to make the radio sensitive and selective, but to avoid oscillation. I have never owned or used such a regenerative receiver, but they seem to perform fairly well, especially given the low circuit complexity. The greatest drawback was that they could oscillate and then cause harmful interference to the neighbors. That's why they were outlawed in the 1930s in most countries. This interference in neighboring receivers caused a howling sound and in Holland it was called the "Mexicaanse hond" (literally Mexican dog).

The superheterodyne receiver became dominant in the 1930s. It offered constant selectivity and sensitivity across the band and it was easier to tune without causing grief to the neighbors. A well-built mediumwave radio from the late 1930s performs as well as any good broadcast radios built after World War 2 (and much better than some of the cheap radios). When FM came around, the emphasis was on making this band work well and less emphasis was put on mediumwave.

Most shortwave communications receivers also perform well on mediumwave. Selectable IF bandwidth and synchronous detectors offer a real advantage.


Transmitting antennas for this band are almost always vertical mast radiators. At the lower end of the band (and on longwave) such antennas are always shorter than a quarter wave and extra capacitance must be added to bring them into resonance. At the higher end of the band quarter wave antennas are feasible.

Most receiving antennas for both mediumwave and longwave are one of the following:

The magic of listening

Words cannot convey exactly what it is like to listen to the crowded mediumwave band at night. Probably most people are not attracted by this cacophony of stations like I am. Well, I am not really attracted by the cacophony, but by the ability to pick intelligible signals from this cacophony, sometimes signals that only would have been intelligible if I could just understand that particular language.

You could hear music on mediumwave from distant countries. That music could not be heard on Dutch stations and those records were unavailable in The Netherlands. The very fact that sound quality was not great and the signal was often disturbed by fading, co-channel interference, adjacent channel interference and man made noise added some to the magic feeling. Then there were the unexpected stations that could suddenly fade in. Of course I also listened to stations that I did expect and desired to hear. On BBC 1 you could hear the latest songs from British bands before they were available in Holland.

Add to this the warm glow of a tube radio, the names of stations on the dial, some of which referred to stations that no longer existed, some of which referred to really distant places. We had a Grundig tube radio at home that had really great mediumwave reception. It had a magic eye, a rotatable ferrite rod antenna and even a flywheel on the tuning capacitor, which gave tuning that special feeling.

Much of the fun of holidays abroad consisted of hearing another radio landscape. Being able to hear Dutch stations from abroad was always very nice.

Modern developments

In the 1980s, AM stereo was introduced in the USA, using the C-QAM system. It is an analog system, almost like transmitting the left channel in the lower side band and the right channel in the upper side band, but not exactly that. It requires a special synchronous detector IC to decode, but ordinary AM detectors get just the mono signal. Many American car radios have it, but comparatively few stations transmit in stereo. Outside the USA there are very few AM stations transmitting in stereo and receivers are essentially unavailable.

The audio frequency range of an AM station is limited to half the channel width. In Europe this is 4.5kHz, in America this is 5kHz. This is a little better than telephone quality, but definitely not hi-fi. For a long time, people have been contemplating digital audio transmissions in these bands. Since 2003 there is a worldwide standard for it, called DRM (Digital Radio Mondiale). You need to compress the audio signal fairly aggressively to get to the bandwidth available on mediumwave or even shortwave. So you can definitely hear the difference between DRM compressed audio and the original. It is often called near-FM quality.

It is possible to mix the IF signal of a radio down from 455kHz to 12kHz. A circuit to do this is fairly easy to build by an amateur. This 12kHz signal can be sampled by the sound card of a PC and special software can decode the DRM signal and send the recovered audio to the soundcard output.

Very few broadcast receivers are available for DRM. As long as this is the case, the system will not see widespread use. Further the system offers all or nothing reception. If all bits are there, you hear a perfectly clear signal, but if the bits of a digital audio frame cannot be recovered, there is complete silence for a few seconds. Where you would just hear a little more noise in an analog signal, you will miss the essential words from a news broadcast in DRM. DRM supports adding more error correction bits to avoid such signal interruptions, but this reduces the number of bits available for the audio signal itself, so it goes from near-FM quality to crappy robot voices. In Europe there are a few DRM transmissions on longwave and mediumwave. In The Netherlands you can hear one from Germany at 1593kHz. On an AM receiver all you can hear is a strong noise.

The USA has its own digital radio system on mediumwave, called HD-Radio (IBOC). Unlike a DRM signal, the signal contains both the analog AM signal and the digital information. The advantage is that the radio can fall back to old school AM if it cannot recover the bits of the digital signal. However, the signal is wider than either a conventional AM signal or DRM signal. Therefore the digital transmissions have to be switched off at night, otherwise they would cause too much interference. It remains to be seen when (or if) digital transmissions will take over this band.

See you next time when we discuss the maritime and tropical bands.

Update 2013-07-10

Some countries (the UK, Germany) have decided to stop broadcasting on longwave and mediumwave by 2015. The Netherlands is likely to do the same and many familiar stations (like the Dutch language Belgian service) and also BBC World Service on 648 have already gone. So we will soon miss many of the major stations on this band. At least in the Western world, there seem to be no serious plans to roll out DRM on this band, but in may happen in very large countries like Russia or India though, which may drive the market for cheap single-chip DRM receivers. The 100th anniversary of mediumwave broadcasting may be a rather silent one, at least in Western Europe.

Update 2016-05-10

I added a band diagram. The Dutch public broadcasters have ceased their mediumwave transmissions in 2015. The Netherlands will continue to use mediumwave for low power AM stations.