signs identifying the different stations 
Author: Rumen Pankov and Ivo Ivanov. 05/12/1910 DXers Area
Signs identifying different
All radio stations before starting your program, issues for several minutes signals repeatedly. The signals are usually fragments of musical works performed in different instruments, voices, birds chirping etc. Sometimes the sounds of the speech signal alternate with in announcing the name of the respective station.
Using this type of introduction radio programs are produced in order to help listeners to adjust their receivers and better tune the respective station. This is especially important in cases where adjacent operating at frequencies other powerful transmitters.
In the last half century many international broadcasters changed their signals driven by different reasons. Some, however, still listening to this day on shortwave.
This is the German public radio, Deutsche Welle, whose call sign is an excerpt from the opera "Fidelio" by Beethoven, namely "It sucht der Bruder seine Bruder."
Also, for decades, Vatican Radio emissions are opened with the phrase "Christus Vincit."
Many of the identification signals are related to the country's national anthem is issued, for example, "O Canada" on Radio Canada and Portugal and Cuba, or fragments emitted military marches and drumming as they did signals with old Tirana Radio, Radio "Voice of the Gospel" of Ethiopia, "The Voice of Israel."
The songs of various bird species endemic to the particular country are used as identification marks of the stations in New Zealand, Australia. In the old signal of Radio Baghdad was heard singing a Nightingale, the radio station Voice of Africa uses sounds of guitar and singing birds, etc.
They are among the most original identification marks the sound of a stream in the Radio Program Two Arabia, the sound of flute and tinkling bells of the Greek Radio, camel bells Radio Cairo.
numerous symphonic works are also used in the identification signals. Radio Prague employs fragment Dvorac's Ninth Symphony, Polish Radio has chosen to Chopin, Radio Romania, Enescu, Radio Austria, the "Beautiful Blue Danube" by Johann Strauss, etc.
fragments of melodies and traditional songs precede the start programs of Radio Japan Radio Netherlands, Radio Ukraine etc.
As we said at the start signals from international broadcasters have been changed. The current Russian radio station "The Voice of Russia now uses music by Borodin, Voice of America uses" Yankee Doodle ", Radio France International is now using the Marseillaise, etc. We have already referred in our previous programs to identify the signs of the old Radio Sofia and Bulgaria Radio today.
not forget that a comprehensive review of all identification signals beyond our strength and it is impossible given the existence, worldwide, thousands of stations, each with its own introductory signal. 
English version by Mikhail Mikhailov
Source: Señales de identificación de las diferentes emisoras http://bit.ly/fLG6k6
Señal de Intervalo
Las señales de intervalo, las utilizan las emisoras de radio de onda corta como presintonía, unos 5 minutos antes de iniciar sus transmisiones. La señal es una melodía, alguna canción característica del país, el himno nacional o una música incidental que no dura más de 30 a 45 segundos y que se repite una y otra vez durante unos 5 minutos, hasta que se da inicio a la transmisión. Sus propósitos son diversos:
Hacer que el oyente pueda identificar fácilmente a la estación, aún si la emisora no transmite en idioma conocido para éste.
Tune the right frequency of transmission.
inform other stations that the channel is busy.
The practice began in Europe in the 1920 and 1930 on shortwave and although it has declined with the digital age, however, has not disappeared. More ..
(Wikipedia http://es.wikipedia.org/wiki/Se% C3% B1al_de_intervalo)
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is quite curious fate of the signals used by Radio Belgrade. used the station until the 70's last century, the communist anthem, that is, the International which happened after the local anthem "Yugoslavia." After a sign was used identification anthem of Serbia and Montenegro and now a radio signal Serbia. 
