The ongoing developments in digital processors have made them incredibly fast. The time to execute software programs (such as electronic functions) became shorter and shorter until the point where traditional analogue signal handling circuits became obsolete.
Today there is a choice to either develop electronic circuits to handle analog electrical signals or transform the electrical signals into numbers that a digital computer can handle. The conversion of signals to numbers we call digitizing signals is done with an electronic circuit called an analog-to-digital converter (ADC). After digital processing, the obtained digital signal can be converted back to a continuous analogue signal.
In most cases the conversion of the signal to the digital domain, handling it by software and reconverting it to the analogue domain is easier, more precise, and less costly than developing a particular electronic circuit to do the same operation.
The method is called digital signal processing. DAB is a typical electronic system that could not be realized by using traditional electronic circuits. The signal processing needs to be so precise that the traditional electronic circuits could never attain the precision needed to make DAB work. DAB is nothing more than a lot of digital signal handling, which a personal computer can handle easily.
In fact, all the audio and base-band signals, even the base-band modulator, can be treated by software on a personal computer.
Only the (analogue) RF part (read transmitter) will have to use traditional electronics.
The RF part can be realized with standard SDR technology (Software Defined Radio). These are standard circuits which receive a digital base-band signal produced by a computer and transform this signal to the RF pass-band to be amplified and transmitted (converted by the antenna in electromagnetic waves).
The SDR circuit is mainly a physical quadrature modulator with a local oscillator whose frequency can be programmed by the connected personal computer (PC) to the requested transmit frequency.
What did we finally learn about DAB?
- In DAB, electrical signals are not handled by electronic circuits but by software algorithms on a computer. So, DAB is mostly electronics by software.
- A necessary electronic circuit to allow signals to be treated by software is the analog-to-digital converter (ADC), which turns continuous signals into discrete number series. Also, the inverse is possible the digital numbers can be converted back into the original continuous signal by a circuit called a digital-to-analogue conversion (DAC).
- To transmit the prepared DAB signal, we use yet another technology named software-defined radio (SDR) circuit. The core of the SDR circuit is the quadrature modulator.
We must understand three important things to understand DAB:
- The many DAB software algorithms (what is the software doing exactly?)
- How are continuous signals transformed to digital signal numbers, and how does the reverse process work?
- What is quadrature modulation, and how the base-band signal becomes a pass-band signal ready for transmission?