Single frequency network

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Below: single frequency network

A single-frequency network , even SFN for English Single Frequency Network , consists of several spatially distributed over a contiguous area transmission systems which in synchronism with each other and using the same transmission frequencies radiate identical information. The aim is to cover a larger, coherent area with a specific broadcast program without using different frequencies.

General

Single frequency network with three transmitters

Normally, spatially adjacent transmission systems - such as radio transmitters - have to use different transmission frequencies even when an identical program is broadcast. The reason for this is that when the same frequency is used, the overlapping of the neighboring illumination zones due to local additive superimposition of the wave fronts ( interference ) leads to fluctuations in the received field strength ( fading ). Both constructive and destructive interferences occur in the overlapping areas (so-called confusion area ); In the worst case, the destructive interference at certain locations in the reception area can lead to the complete cancellation of the transmission signal.

In single-frequency networks, the effects of interference are compensated for by technical measures during information transmission. Several factors are very important in the implementation:

  1. All transmitters must broadcast the same information at the same time, for example an exactly identical radio program.
  2. The transmission frequency must be the same for all transmitters or have a slight deviation of a few Hertz (so-called phase rigidity ). The first case is referred to as a synchronous single-frequency network, the latter as an asynchronous single-frequency network.

In both synchronous and asynchronous single-frequency networks, constructive or destructive interference also occurs in the overlapping areas. In asynchronous single-frequency networks, the location and time of this interference change roughly with the frequency difference of the transmitters, creating a beat .

The interferences are always frequency selective. This means that a certain frequency f 1 is extinguished by interference at a certain spatial point in the overlap area, but this does not apply to another frequency f 2 ( f 1 ≠ f 2 ) at the same point , even if these frequencies are the same Antennas is broadcast. The cancellation occurs at the same time for even multiples ( harmonics ). When operating single- frequency networks, this fact is used by the fact that the information to be transmitted is transmitted redundantly over different carrier frequencies within a frequency band , whereby at least one frequency is always available for (relatively) undisturbed reception. Digital single- frequency networks are based on digital modulation methods with multiple carriers, such as Coded Orthogonal Frequency Division Multiplex (COFDM), a modulation method based on Orthogonal Frequency Division Multiplex (OFDM). Regardless of the single- wave technology, a receiver with a directional antenna can also be used, the antenna of which is aligned in such a way that only the signal from a single transmitter is received, or demodulation using the single sideband method can also be used.

Single frequency networks on medium wave

With the expansion of the European broadcasting network around 1930, there was an interest in broadcasting the same information simultaneously over a large area from several transmitters. In the German Reich, Großdeutsche Rundfunk established the first single- frequency networks in the medium-wave range from 1941 . In that time there was

  • South German single wave (519 kHz; Dornbirn, Innsbruck, Nuremberg, Salzburg)
  • West German single wave (1195 kHz; Frankfurt a. M., Kassel, Koblenz, Trier)
  • Silesian single wave (1231 kHz; Gleiwitz, Reichenbach / Oberlausitz)
  • Ostmark single wave (1285 kHz; Graz, Klagenfurt, Kötschach, Lienz, Radenthein, Spittal, Villach)
  • North German single wave (1330 kHz; Bremen, Flensburg, Hanover, Magdeburg)

These networks were essentially retained until the 1948 Copenhagen Wave Conference. According to the 1948 Copenhagen Wave Plan , medium wave was expanded to 1602 kHz from March 1950 and new single-frequency networks were set up in the additional frequency range.

  • English single waves (1214, 1457 and 1546 kHz)
  • French single wave (1403 kHz)
  • International single waves (1484 and 1594 kHz)
  • Italian single waves (1331, 1448 and 1578 kHz)
  • Yugoslav single wave (1412 kHz)
  • Moroccan single wave (1043 kHz)
  • Norwegian single wave (1602 kHz)
  • Austrian single waves (1394 and 1475 kHz)
  • Portuguese single waves (1562 and 1602 kHz)
  • Swedish single wave (1562 kHz)
  • Swiss single wave (1562 kHz)
  • Spanish single waves (1538, 1570 and 1586 kHz)
  • Czechoslovak single wave (1520 kHz)

For German broadcasting, limited single-frequency networks (per frequency to 70 kW total transmission power) were allocated in the Allied occupation zones:

  • German broadcasting in the American zone (989 and 1602 kHz)
  • German broadcasting in the British zone (971 and 1586 kHz)
  • German broadcasting in the French zone (1196 and 1538 kHz)
  • German broadcasting in the Soviet zone (1043 and 1546 kHz)

From November 1978 onwards, numerous simulcast waves were approved for Germany by the Geneva Wave Plan .

  • DLF single waves (549 and 756 kHz)
  • HR single wave (594 kHz)
  • BR single waves (520 and 801 kHz)
  • WDR single wave (702 kHz)
  • SDR single waves (711 kHz and 1413 kHz)
  • RIAS single wave (990 kHz)
  • AFN single waves (1107 kHz, 1143 kHz and 1485 kHz)

After medium wave reception in Germany became largely insignificant from 2009, some single-frequency networks will still be retained.

  • AFN single wave 1107 kHz (Amberg, Grafenwöhr, Vilseck)
  • AFN single wave 1143 kHz (Geilenkirchen, Spangdahlem)
  • AFN single wave 1485 kHz (Ansbach, Garmisch, Hohenfels, Illesheim)

In Austria and Switzerland, there are no longer any medium wave frequencies used in single-wave operation.

Single frequency network on VHF

In Germany there are several VHF single-frequency networks in the Frankfurt - Wiesbaden area. One that combines two broadcasting sites of the broadcaster Radio BOB in Frankfurt and Wiesbaden with the frequency 101.4 MHz and is operated by Uplink Network . Also antenna Frankfurt 95.1 is powered by a single frequency network, which spreads the frequency 95.1 MHz of the locations Frankfurt (Main) Europe tower and Wiesbaden / Konrad Adenauer ring. The youth radio planet radio in Kassel and Eschwege is also broadcast via simulcast .

Digital applications

Typical single-frequency networks are digital terrestrial television DVB-T based on the COFDM modulation method or digital multimedia broadcasting (DMB) used in mobile devices . In the case of radio programs, simulcast operation is used in Digital Audio Broadcasting (DAB).

Single frequency networks are also used in the area of authorities and organizations with security tasks such as BOS radio . Adapted single-frequency networks are used in radio navigation such as LORAN-C .

See also

Community wave

literature

Web links

Individual evidence

  1. ↑ www.dxradio-ffm.de: Frequency list 1942
  2. ↑ www.dxradio-ffm.de: Frequency list 1947
  3. ↑ www.dxradio-ffm.de: Frequency list according to the Copenhagen Wave Plan from 1950
  4. ↑ www.dxradio-ffm.de: Frequency list according to the Geneva Wave Plan from 1978
  5. ^ American Forces Network Europe: AFN Europe Radio Frequencies
  6. ↑ UPLINK operates VHF simulcast in Hesse. In: www.uplink-network.de. Retrieved July 1, 2016 .
  7. ↑ Planet Radio. In: fmscan.org. Retrieved July 4, 2016 .