Noise blanking

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Noise blanking ( English interference blanking ) is u. a. for use in commercial or semi-professional receivers .

In the IF amplifier are short-term glitches detected and the IF signal completely blanked for the duration of the disruption. Since the detection of a glitch takes a certain amount of time, the blanking electronics are usually located after a ceramic filter . The transit time of the filter compensates for the detection time for the interference pulse so that only the interference pulse is eliminated.

However, since blanking in narrowband IF amplifiers also has negative effects, interference blanking can always be switched off.

Short, crackling background noises, such as B. caused by unsuppressed ignition systems can be effectively combated. Noise blanking improves reception for all types of modulation, but is particularly effective with amplitude modulation .

Very similar disturbances occur due to dirt and scratches with record scanning and optical sound . You can get rid of them in the following ways:

  • Offline processing on the computer with suitable software and partly by hand;
  • Playback via a computer or DSP (digital signal processors) using suitable software ;
  • electronic circuit for noise blanking, the disturbances in the playback of records u. a. recognizes that it detects frequency components above the LF range of the record.

What all these noise blanking techniques have in common is that the signal is available more or less delayed and the blanked gaps must be filled again:

  • in the simplest case by linear interpolation ;
  • more complex by analyzing the frequency spectrum of the audio signal and interpolation with a higher order.

In any case, a loss of information in the mathematical sense is to be expected in the event of interference blanking. Under certain circumstances, acoustic events can be lost (e.g. the sound of a crackling fire).

literature

  • Gregor Häberle, Heinz Häberle, Thomas Kleiber: Expertise in radio, television and radio electronics. 3rd, revised and expanded edition. Verlag Europa Lehrmittel, Haan-Gruiten 1996, ISBN 3-8085-3263-7 .
  • Helmut Röder, Heinz Ruckriegel, Heinz Häberle: Electronics. Volume 3: Communication Electronics. 5th edition. Verlag Europa Lehrmittel, Wuppertal 1980, ISBN 3-8085-3225-4 .