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Section 3
Transmitters and Receivers
SDR transmitters and receivers
3M1 Recall that the SDR receiver takes in all electromagnetic signals from the antenna and digitises this input for processing in the CPU (Computer)software.
Diagram of an SDR Receiver
As with a standard
receiver the SDR (Software Defined Radio) receiver receives all the
electromagnetic RF from the antenna and converts those analogue signals to a
digital format for processing in
Software. Software is a set of instructions that a computer uses to
process information.
First of all it is converted in an ADC (Analogue to Digital
Converter)which takes high speed samples or slices of the incoming RF. It is then passed
to the CPU (Central Processing Unit - or computer)which uses a DDC (Digital Down Converter) for processing the signals.The CPU works
out the Parameters requested by the user.
In a nut shell the a SDR Receiver has a rather special computer which makes sense of a digital signal which you and I would not be able to comprehend. This computer is also known as a DSP - Digital Signal Processor
Recall that a mathematical operation enables all the signals to be sifted into separate frequency components.
Being digital means that it is all about numbers and as such a mathematical operating in the receiver to enable (convert) the signals into separate frequency components such that it can be understood as normal audio.
Recall that the required signal is selected using a filter defined in software.
The required signal is selected by the user and is processed in the CPU using a filter which is built into the software.
Recall that demodulation is carried out in software.
The demodulation of the digital signal is carried out in software.
So just to go through it again - The SDR receiver converts the incoming radio signals to digital format so that filtering and demodulation can be carried out on the signal using software.
Recall that Software Defined Radio (SDR) receivers convert incoming signals to digital format and then perform filtering and demodulation on the signal using software. SDR transmitters (below) generate modulated radio signals using software.
Diagram of an SDR Transmitter
A signal which has been generated in an SDR transmitter is formed from a modulated audio signal using software in reverse fashion to how an SDR receiver works. In the transmitter the CPU uses the signals from a DUC (Digital Up Converter) and passes them through to the RF (radio Frequency) stages and on to the aerial.
So all in all both the transmitter and receiver rely upon (CPU's) computers running software to perform many of the tasks.
The origin of some of the text on this page is from the RSGB with additions by the web master
