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Digital Radio Is Coming, Pt.4

In this final instalment we discuss the signal formats and give a comparison of DAB+ and DRM. Also included is a brief discussion of antennas suitable for DAB+ reception.

by Alan Hughes

Digital TV & radio systems have two reception conditions. They either provide good sound and picture quality or there is no reception at all.

Perhaps we should qualify this by saying that when you are on the brink of signal failure, digital TV can be plagued with partial pixellation of the picture and loud clicking in the sound as it drops in and out.

So under a variety of reception conditions, there is no gradual reduction of sound and picture quality.

To produce the designed quality there must be adequate signal and no noise, particularly impulse noise. Impulse noise is generated by lightning strikes, electrical switching, arcing power line insulators, arcing in brush motors and unsuppressed ignition systems in petrol motors.

So for digital radio it is important to get reliable reception otherwise the sound will have annoying gaps in it.

Click for larger image
A single Audio Superframe. Five blocks of synchronisation, transmitter identification and Fast Information Channel data, shown in black, white and grey have been inserted.
Click for larger image
Three Audio Units shown in three rows. This is a single Audio Superframe, which contains 120ms of audio

Errors in digital radio systems

The effects of errors are:

Corrected Errors are not detectable by the listener. 8% of the transmitted signal is mathematically related to the data being sent. So the additional error correction data can be used to correct errors in the main signal.

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