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2F1 Recall that analogue signals are constantly
changing in amplitude, frequency or both.
In the A.C. theory section we learnt that a sine wave is constantly varying in amplitude and is an analogue signal. When two analogue signals mix in a transmitter, say for example 50Hz and 500Hz, the lower frequency will modulate the higher frequency to produce an Amplitude Modulation or a Frequency modulation signal, depending upon the method used. An AM signal will vary in size at the higher frequency, and an FM signal will vary in length at the higher frequency.
There are several other types of modulation which we will learn about later.
Recall that digital signals are a stream of finite values at a specific sampling interval.
Some modern receivers are software defined radios (SDR). In the front end of their receiver, the analogue radio signals are effectively chopped into may thousands of pieces of digitised information by an electronic device called an analogue to digital converter (ADC). You will learn more about these later.
Recall that digital signals can be processed by a computing device with suitable software.
These digitised signals are then processed using a computer or CPU chip in the radio, by using mathematical techniques the audio can be recovered, filtered, displayed, and passed out to a loudspeaker.
2F2 Recall that an Analogue to Digital Converter (ADC) is a device used to sample an analogue signal and produce a digital representation of it.
The digital representation is a string of binary 0's and 1's which can be understood by the computer software. Typically used in all sorts of computerised devices, even like your mobile phone, the ADC together with software can improve the quality of performance. This can be further improved by software updates.
Recall the meaning of the term ADC.
An ADC (Analogue to Digital Converter) converts the analogue waveforms into a digitised output for further processing.
Recall that a Digital to Analogue Converter (DAC) is a device used to represent a digital signal in analogue format.
We also have another electronic device that does the opposite to an ADC. This is called a digital to analogue converter (DAC). This takes a digitised binary signal and converts it back into an analogue signal.
Recall that a computing device is required to process digital signals.
In a modern radio receiver or transmitter using ADC and DAC techniques, there is a need for a computer to process the digital information. This is done by software using mathematical techniques.
Recall the meaning of the term DAC
DAC's is an acronym for Digital to Analogue Converter which is used to convert computer binary signals (Digital Signals) into analogue signals.
The origin of some of the text on this page is from the RSGB with additions by the web master
