The ham radio receiver of the 21st century is mostly software.
It is called a Software Defined Radio or SDR for short.
Out of the many features and advantages of a SDR receiver, I particularly like its effectiveness in picking extremely weak signals out of the noise and surrounding interference.
One can narrow down the bandpass filter to just enough for the signal one wants to receive. The SDR filters are truly like "brick walls" that one can erect around the wanted signal. Best of all, there is no annoying "ringing" on top! Just a pure signal. :)
First, as with any other radio receiver, the antenna is connected to the SDR's "hardware" RF front-end. Its purpose is to...
The departure from a conventional receiver starts here.
The amplified IF analog signal produced by the RF front-end is fed to an analog-to-digital-converter (ADC).
The digital output of the ADC is then fed to a Field Programmable Gate Array (FPGA).
All of the signal demodulation and spectral functions are done by the SDR software on your PC.
Most SDR ham radio receiver implementations will usually (at least) support AM, WFM, USB, LSB, N-FM, DSB and CW with fully adjustable DSP filter bandwidths ... down to below 1 Hz in some cases!
The SDR is hosted by the O/S of your computer, just like any other application. The majority of the SDR implementations run on some flavor of Microsoft Windows®.
However, an increasing number of SDR projects are now turning to the Linux open source operating system which offers...
On top of its higher performance and flexibility, a SDR offers ham radio operators the neat advantage of being able to add new functions and features to their ham radio receiver at no cost!
Noteworthy SDR implementations are:
I have to mention here the exceptional transceivers produced by FlexRadio Systems™. You have to hear the signals you receive with them to believe their published outstanding specs!
For more on SDR types and for links to research and development projects, see this fine SDR resource maintained by F4DAN.
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