Single-frequency network

A single-frequency network SFN for the English name Single Frequency Network, consists of several spatially over a contiguous area distributed transmitters, which sync with each other and emitting identical information using the same transmission frequencies. The goal is for a larger, contiguous area with a particular broadcast program to provide without having to use different frequencies.

General

Normally, must be spatially adjacent transmitting equipment such as radio transmitters to broadcast television programs, even when broadcasting of an identical program, using different transmission frequencies. The reason is that comes from the overlap of the adjacent illumination areas it by additive superposition of the local wavefronts (interference ) to variations in the reception field strength (fading). In the worst case, it may come at certain locations of the reception area to the complete extinction of the transmitted signal at the destructive interference so-called.

Exist in single-frequency networks the same physical limitations, however, the effects of interference are compensated by additional technical measures in information transmission. When implementing several factors are very important:

Both synchronous and asynchronous frequency networks occurs in the overlap areas to constructive or destructive interference (so-called confusion area ). For asynchronous single-frequency networks, the location and time of this interference in some change with the frequency difference of the transmitter, a beat created.

The interferences are always frequency-selective. This means that a certain frequency F1 is eliminated at a specific point in space in the overlapping area due to interference, but this at the same point for a different frequency f2 (f1 ≠ f2) does not apply. The extinction occurs at the same time for even multiples of ( harmonics). In the operation of SFNs one takes advantage of this fact by the information to be transmitted is transmitted redundantly on different carrier frequencies within a frequency band, which is always at least one frequency for the (relatively) undisturbed reception available. Modern digital simulcast networks usually use digital modulation schemes with multiple carriers such as Coded Orthogonal Frequency Division Multiplexing ( COFDM), one on Orthogonal Frequency Division Multiplex ( OFDM) based modulation methods. Alternatively, a receiver may be used with a directional antenna, the antenna is oriented such that only the signal of a single transmitter is received, or it may be a single-sideband demodulation after applied.

SFNs on medium wave

With the expansion of the European broadcasting transmitter network in 1930 one was interested to transfer a large area of several transmitters simultaneously same information. In the German Empire of the Great German Radio established in 1941, the first single-frequency networks in the medium-wave band. During this time there was the

  • Süddeutsche single-frequency (519 kHz; Dornbirn, Innsbruck, Nuremberg, Salzburg)
  • West German single-frequency ( 1195 kHz; Frankfurt, Kassel, Koblenz, Trier)
  • Silesian single frequency ( 1231 kHz; Gliwice, Reichenbach / Upper Lusatia )
  • Ostmark single frequency (1285 kHz, Graz, Klagenfurt, Kötschach, Lienz, Radenthein, Spittal, Villach )
  • North German single-frequency (1330 kHz; Bremen, Flensburg, Hannover, Magdeburg )

These networks were maintained up to the Copenhagen conference in 1948 essentially wave after wave of Copenhagen 1948, the plan was extended to medium wave 1602 kHz from March 1950 and in the frequency range of additional new frequency networks have been established.

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

For the German Broadcasting Limited SFNs were assigned (per frequency to 70 kW total transmit power ) in the Allied zones of occupation:

  • German radio in the American zone: 989 and 1602 kHz
  • German radio in the British zone: 971 and 1586 kHz
  • German radio in the French zone: 1196 and 1538 kHz
  • German radio in the Soviet zone: 1043 and 1546 kHz

In the postwar period have been approved by the Geneva wave plan from November 1978 onwards numerous simulcast for Germany.

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

After the medium wave reception in Germany has become largely irrelevant from 2009, although some frequency networks will continue to maintain

  • DLF single-frequency 549 kHz ( 100 kW Northern churches, Bayreuth Thurnau 100 kW)
  • DLF single-frequency 756 kHz (Braunschweig 200 kW, 100 kW Ravensburg )
  • BR single-frequency 729 kHz ( 1 kW Würzburg, Hof 0.2 kW)
  • BR single-frequency 801 kHz (Munich - Ismaning 100 kW, Nuremberg - Dillberg 17 kW )
  • AFN single-frequency 1107 kHz ( Amberg, Baumholder, Grafenwöhr, Kaiserslautern, Pirmasens, Vilseck )
  • AFN single-frequency 1143 kHz ( Bamberg, Geilenkirchen, Heidelberg, Mannheim, Schweinfurt, Spangdahlem, Stuttgart)
  • AFN single-frequency 1485 kHz ( Ansbach, Garmisch, Hohenfels, Illes Home )

In Austria and Switzerland, there are no used in simulcast medium wave frequencies more.

Digital Applications

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

Frequency networks are also used in the field of authorities and organizations with security tasks such as the bad radio. Adapted frequency networks are used in radio navigation, such as LORAN -C.

Overlap zone Bandwidth (signal processing) Medium frequency Geneva Frequency Plan of 1975 Deutschlandfunk Hessischer Rundfunk Bayerischer Rundfunk Westdeutscher Rundfunk Rundfunk im amerikanischen Sektor Ravensburg mediumwave transmitter Ismaning radio transmitter
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