If you've heard the phrase "shortwave listeners", you might have wondered what on earth that was all about.

It relates to the length of a radio wave used to transmit information. The length of a radio wave is tied to its frequency. The longer the wave, the lower the frequency.

When radio amateurs talk about bands, like for example the 40m band, we're talking about a range of frequencies where the wavelength is around 40m. From a frequency perspective, this is around 7 MHz. The 160m band, at about 1.8 MHz, or 1,800 kHz is considered the beginning of the short wave bands.

This implies that there are longer waves as well. If you've ever seen or owned a mid 1980's transistor radio, you'll have seen the notation MW, which stands for Medium Wave, today it's called the AM band. Older radios might have the notation LW, or Long Wave.

The medium wave band is a broadcast radio band that runs between about 500 and 1,700 kHz. The wave length is between 600 m and 170 m.

When radio was still in its infancy, there was also a popular long wave band, with wavelengths between 800 m and 2,000 m, or 150 to 375 kHz.

Today much of that has gone by the wayside. With the advent of digital radio, in Australia it's called DAB+, Digital Audio Broadcasting, the whole idea of "wave" has pretty much vanished.

Some countries like Japan and the United States are in the process of discussing the phasing out of the AM broadcast band. Much of that appears to be driven by car manufacturers who claim that the AM band is no longer useful or used, but forget to tell anyone that they really want to stop having to put AM radios in their cars because it's difficult to isolate the electrical noise from their modern contraptions in order to make it possible to actually listen to that band.

If you ask me, it's a good incentive to make electronics RF quiet, something which is increasingly important in our wirelessly connected world.

This might lead you to believe that all activity on air is moving to higher and higher frequencies, but that's not the case. The properties that made long wave and medium wave radio possible in the early 1900's are still valid today. For example, there are WSPR or Weak Signal Propagation Reporter beacons on the 2200m band, or at 136 kHz.

Whilst your RTL-SDR dongle might not quite get down that low, most of them start at 500 kHz, you don't need to spend big to start playing. My Yeasu FT-857d is capable of tuning to 100 kHz, plenty of space to start listening to the 2200m band, even if I cannot physically, or legally, transmit there.

If you want to build your own receiver, you can check out the weaksignals.com website by Alberto I2PHD where you'll find a project to build a receiver capable of 8 kHz to 900 kHz using a $50 circuit board.

If that's not enough, there's radio experimentation happening at even lower frequencies. Dedicated to listening to anything below 22 kHz, including natural RF, with a wavelength greater than 13 km, Renato IK1QFK runs the website vlf.it where you'll find receivers and antennas to build.

Given that most sound cards operate up to around 192 kHz, you can start by connecting an antenna to the microphone port of your sound card and use it to receive VLF or Very Low Frequencies. On your Linux computer you can use "Quisk" to tune.

There are VLF transmitters on air. For example, SAQ, the Grimeton Radio Station in Sweden opened on the 1st of December 1924. Capable of 200 kW, today it uses about 80 kW and transmits twice a year on 17.2 kHz.

While we search for higher and higher frequencies, there is still plenty of fun to be had at the other end of the radio spectrum. Consider for example that VLF or Very Low Frequency radio waves, between 3 and 30 kHz can penetrate seawater.

I'll leave you to explore.

I'm Onno VK6FLAB

The origin of our amateur bands

It's hard to imagine today, but there was a time when there was no such thing as either the 80m or the 20m amateur band, let alone 2m or 70cm.

Picture this. It's the roaring 20's, the 1920's that is. Among a Jazz Age burst of economic prosperity, modern technology, such as automobiles, moving pictures, social and cultural dynamism, the peak of Art Deco, we're also in the middle of a radio boom where the world is going crazy buying radios as fast as they can be constructed, there are hundreds of licensed broadcasters, the bands are getting crowded, radio amateurs have been banned from the lucrative radio spectrum above 200 meters, and can only play in the "useless short waves" using frequencies greater than 1,500 kHz. And play they did.

On the 2nd May 1925 amateurs proved they could communicate with any part of the world at any time of the day or night when Ernest J. Simmonds G2OD and Charles Maclurcan A2CM made a daylight contact between Meadowlea, Gerrards Cross, Buckinghamshire, England, and Strathfield, Sydney, New South Wales, Australia on what we now call the 20m band. This contact occurred not once, but regularly, for several days, using 100 Watts.

To give you a sense of just how big news of this feat was, on the second scheduled contact the Prime Minister of Australia, Stanley Bruce, sent a message to England's Prime Minister, Stanley Baldwin: "On occasion of this achievement Australia sends greetings."

If you recall, the IARU, the International Amateur Radio Union, was a fortnight old at this point. Less than a year later contact was made using voice.

Between the banning of radio amateurs from frequencies below 1,500 kHz at the London International Radiotelegraph Conference in 1912 and the Washington International Radiotelegraph Conference in 1927 the world had irrevocably changed. In 1912 the discussion was almost all about ship to shore communication. By 1927, the world had tube transmitters, amplitude voice modulation, higher frequencies and what the 1993 IARU President, Richard Baldwin, W1RU calls, "literally an explosion in the use of the radio-frequency spectrum".

In 1927 individual countries were beginning to control the use of spectrum, but there was no universal coordination, no international radio regulation and as we all know, radio waves don't stop at the border.

Richard W1RU, writing in 1993 says: "In retrospect, the Washington conference of 1927 was a remarkable effort. It created the framework of international radio regulation that exists even today. It had to recognize and provide for a multitude of radio services, including the Amateur Service. It was at this conference that amateur radio was for the first time internationally recognized and defined. Bands of harmonically related frequencies were allocated to the various radio services, including the Amateur Service."

While the IARU was two years old, it really hadn't represented amateur radio on the international stage, until now.

The 1927 conference defined an "amateur" as a "duly authorised person interested in radio electric practice with a purely personal aim and without pecuniary interest."

The harmonically related frequencies that were allocated to the Amateur Service are recognisable today. I'll use current band names to give you some context.

1,715 kHz to 2 MHz, or 160m, 3.5 to 4 MHz, or 80m, 7 to 7.3 MHz or 40m, 14 to 14.4 MHz or 20m, 28 to 30 MHz or 10m, and 56 to 60 MHz or 6m.

Of those, the 20m and 80m bands were exclusive to amateurs. The 10m and 6m bands were shared with experimenters and the 160m and 80m bands were shared with fixed and mobile services. You'll notice the absence of bands we use today, the 2m and 70cm bands, 15m and the so-called WARC bands to name a few.

The final ratified document goes into great detail about the requirements, the restrictions, how to deal with interference, how to allocate frequencies and numerous other provisions, many of which will look familiar, almost a hundred years later, if you've ever looked at the rules and regulations under which you operate as a licensed amateur today.

There were various radio amateurs at the 1927 conference, but as Richard W1RU puts it: "much of the credit for the success of amateur radio at that conference has to go to two representatives of ARRL -- Hiram Percy Maxim, president of ARRL; and Kenneth B. Warner, Secretary and General Manager of ARRL."

While Richard points to their roles in the ARRL, you might recall that Hiram was elected international president of the IARU and Kenneth its international secretary-treasurer.

Whichever way you look at it, whichever organisation you credit, today we have amateur bands thanks to those efforts made nearly a century ago.

I'm Onno VK6FLAB