Longwave

In radio, longwave refers to parts of radio spectrum with relatively long wavelengths. The term is a historic one dating from the early 20th century, when the radio spectrum was considered to consist of long, medium and short wavelengths. Most modern radio systems and devices use wavelengths which would then have been considered 'ultra-short'.

In contemporary usage, the term longwave is not defined precisely and its meaning varies across the world. In the US, for example, the Longwave Club of America is interested in "frequencies below the AM broadcast band",^[1] i.e. all frequencies below 535 kHz. (Lower frequencies correspond to longer wavelengths.)

In Europe and other parts of ITU Region 1, where a range of frequencies between 148.5 and 283.5 kHz is used for AM broadcasting (in addition to the medium wave band), the term longwave usually refers specifically to this broadcasting band.

The Region 1 longwave broadcast band falls wholly within the low frequency band of the radio spectrum (30–300 kHz); broader definitions of longwave may extend below and/or above it.

Non-broadcast use

Non-directional beacons

Non-directional beacons transmit continuously for the benefit of radio direction finders in marine and aeronautical navigation. They identify themselves by a callsign in Morse Code. They can occupy any frequency in the range 190–1750 kHz. In North America they occupy 190–535 kHz. In ITU Region 1 the lower limit is 280 kHz.

Time signals

There are stations between 40–80 kHz that transmit time signals to radio clocks. For example:

• WWVB in Colorado on 60 kHz.
• DCF77 in Frankfurt am Main, Germany on 77.5 kHz.
• HBG in Prangins, Switzerland on 75 kHz.
• JJY in Japan on 40 & 60 kHz.
• 66.6 kHz in Taldom transmitter, Russia.
• 50 kHz in Irkutsk, Russia.
• MSF time and 60 kHz frequency standard transmitted from Anthorn in the UK

Radio controlled clocks receive their time calibrations signal with built-in longwave receivers. They use longwave, rather than shortwave or mediumwave, because the accuracy of the clocks is not affected by the time signal's travel from the transmitter to the ionosphere and to the receiver; as longwave travels by groundwave, rather than skywave.

Military communication

The United Kingdom, Russian Federation, United States, Germany, and Sweden use frequencies below 50 kHz to communicate with their submarines.

LowFER

In North America during the 1970s the frequencies 167, 179 and 191 kHz were assigned to the short-lived Public Emergency Radio of the United States. Nowadays the 160–190 kHz range is used in the United States for Part 15 LowFER amateur and experimental stations, and the 190–435 kHz band is used for navigational beacons.

Broadcasting

Longwave is used only within ITU Region 1. Most of the longwave broadcasters are in Europe, the former Soviet Union and Mongolia. The rest are located in Turkey, Algeria, Morocco, Western Sahara, and Libya. Saudi Arabia, Egypt, Qatar and the United Arab Emirates have vacant low powered broadcasting allocations.

Typically, a larger area can be covered by a longwave broadcast transmitter than a medium-wave one. This is because ground-wave propagation suffers less attenuation due to limited ground conductivity at lower frequencies.^[2]

Carrier frequencies

Carrier frequencies are exact multiples of 9 kHz ranging from 153 to 279 kHz, except for two stations in Germany on 177 kHz and 183 kHz.

Until the 1970s, some longwave stations in the Soviet Union operated on frequencies as high as 400 kHz, and there was even a station on 433 kHz in Finland.^[3]

Some stations, for instance Droitwich in the UK, derive their carrier frequencies from an atomic clock. They can be therefore used as frequency standards. Droitwich also broadcasts a low bit-rate data channel, using narrow-shift phase-shift keying of the carrier, for Radio Teleswitch Services.

List of longwave broadcasting transmitters

Legend:

^[4][5]

Notes and references

See also

• Low frequency: for other uses (military, commercial and amateur) of this part of the radio spectrum (30–300 kHz)
• Electromagnetic spectrum: Very low frequency, Shortwave, Ground wave, Skywave, Medium wave
• Radio broadcasting: AM broadcasting, BBC Radio 4, BBC Light Programme, Radio clock, Office de Radiodiffusion-Télévision Française, Warsaw radio mast, Digital Radio Mondiale, International broadcasting,
• Shipping: Global navigation satellite system, Navigation, Shipping Forecast
• Lists: List of wave topics
• Other: 1 kilometre, National Institute of Standards and Technology, Fail-safe, WGU-20

External links

• Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page.
• The Medium Wave Circle - The premier club for MW/LW enthusiasts
• Medium Wave News - Published regularly since 1954
• Euro-African Medium Wave Guide
• Longwave Club of America
• How to receive DRM from Kalundborg longwave station
• Klawitter, G.; Oexner, M., Herold, K. (2000). "8.2 Langwellenrundfunk" (in German). Langwelle und Längstwelle. Meckenheim: Siebel Verlag GmbH. pp. 116–131. ISBN 3-89632-043-2. 
• Busch, Heinrich (2001-11-14). "Luftschiff Graf Zeppelin LZ127". http://www.seefunknetz.de/lz127.htm  (German)
• [1]
• http://www.mwlist.org/mwlist_quick_and_easy.php?area=1&kHz=153 - List of long- and mediumwave transmitters with GoogleMap-Links to transmission sites