Baseband

In communication engineering, the baseband is the natural frequency of the useful signal ( lower frequency limit

The assigned frequency band is expressed by the value of the bandwidth B. Real baseband signals have both positive and negative spectral components; the bandwidth therefore extends symmetrically from -B to B. Digital modulation types other hand, are usually processed in the complex baseband, the asymmetrically extends from -B / 2 to B / 2.

In the radio technology, the information signal is to be transmitted before the modulation and after the demodulation, " baseband ", so-called baseband.

In the other stages of the transmission (that is, after modulation and before demodulation ), the useful signal is then modulated onto a carrier, or it is in the intermediate frequency (carrier frequency and band-pass position ).

Applications

As a concrete example of a baseband transmission, the analog telephony was mentioned in a land line: Frequencies are transferred to 3400 Hz at the telephone connection in the base band of 300 Hz. That is, a certain tone with a frequency of 1000 Hz, for example, is represented in the phone cord as an electrical signal with a frequency of 1000 Hz.

Other applications of baseband transmissions are to be found for example in the LAN area as Ethernet and Token Ring. Even television signals passing through SCART or video terminals on the TV are located in the base band - as opposed to signals via antenna jacks.

For example, when used on lines multiplexing for simultaneous transmission of multiple signals, the baseband transmission is no longer possible. In the case of Frequenzmultiplexens the base band signal is shifted by the modulation to a higher frequency range.

In radio communications, it is always necessary to modulate the baseband signal onto a carrier frequency as or do not let the low frequencies of a baseband signal transmitted by radio usually difficult. By choosing different carrier frequencies so several transmitters can transmit simultaneously without interfering with each other. With a pure baseband transmission on a shared transmission channel, there would be solid mutual interference and disturbance.