Scheda Audio come Generatore di Segnali: Il PC come Trasmettitore di Prova DCF77

Il teorema di Shannon sul campionamento afferma che un segnale di frequenza f può essere catturato completamente campionando a 2f. Le moderne schede audio dei PC supportano frequenze fino a 192 k campioni/s, sufficienti per segnali al di sotto dei 96 kHz. Ciò rende possibile generare un segnale orario di prova compatibile con quello a 77,5 kHz dell'emittente Tedesca DCF77.

According to Shannon’s sampling theorem, it is sufficient to sample a signal of frequency f at a rate of 2f in order to capture all of its information. Many sound cards in today’s standard PCs support sampling rates of up to 192 kSamples/s, which, by this theorem, is adequate for signals with frequencies below 96 kHz. This means it is possible to generate the German time signal DCF77 at 77.5 kHz as well. The present article demonstrates how this can be done.

Signal Generation

If you want to generate signals with a sample rate of 192 kSamples/s, you must generate one sample every 5.208 µs. That alone is already quite fast; additionally, on a PC, several applications usually use the available computing power. Generating one sample exactly every 5.208 µs is therefore unrealistic, which is why buffers are used. The structure of the signal processing chain then looks like in Figure 1.