Radio operator FM

The radio operator FM is a radiophonic technique of diffusion of the sound which uses the Frequency modulation (or FM for Frequency modulation ) of the waves radio.

The radio stations FM emit on the Fréquence S of the band 87,5-107,9 MHz called band of the Ondes Extremists Short OUC (initially from 87,5 to 104 but which overflowed then with the arrival of stations of Japanese manufacture).

The January 5th 1940, a demonstration of the radio FM in front of FCC ( federal Commission of the communications American ) was carried out for the first time.

March 1st 1945, W47NV started to emit with Nashville (Tennessee), becoming the first radio station FM.

The emissions can be in stereophonic Monophonique or . However, certain stations emit only into mono. In all the cases, the mono signal (G+D) is emitted from 0 to 15 Khz, which ensures a decoding by the mono receivers as well as stereo.

In the emissions in stereophony, one emits in more the differential of the ways (GD) around carrying to 38 Khz. Carrying additional to 19 Khz allows the detection of the emissions in stereophony by the compatible receivers. The receiver can pass in stereo or mono mode according to the quality of reception of the signal. To obtain the ways left or right-hand side, the receiver quite simply makes the sum or the difference of the two signals “G+D” and “GD”.

A signal complementary to 57 Khz makes it possible to transmit numerical informations (RDS, Radio dated system): inter alia, the name of the station, close frequencies in order to follow the changes of frequency at the time of a voyage, etc

Thus for example, with radio operator emitting in stereophony and using the RDS, the result will be:

  • a signal “G+D” of 30 Hz with 15   000 Hz (around the Carrying )
  • a signal controls of 19   000 Hz
  • a signal “GD” of 23   000 Hz with 53   000 Hz (around the Sous-porteuse with 38   000 Hz)
  • a signal RDS (around the subcarrier with 57   000 Hz)

Foot-note: the term “bandages FM” is unsuitable, because the Frequency modulation (FM) can be realized on any frequency thus in any Waveband. The official French denomination is “band OUC - Waves Short Extremists”. The term “bandages FM” finds its origin in the fact that only the Radio FM emitted in VHF - Bande II (of 87,5 with 107,9  MHz), and thus this beach of frequency is now called, in an inappropriate way, “bandages FM”.

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