What is SDR and webSDR in amateur radio?

What is SDR and webSDR in amateur radio?

In my younger days when I was a very active amateur radio operator, the state of the art was a superheterodyne receiver, called in short as a superhet. Superhet had a local oscillator and converted the received high frequency into a lower intermediate frequency for more efficient processing. Prior to that it was a simple tuned circuit with amplification of a rectified signal, which had problem with selectivity. Now when I am trying to return back to the hobby after retirement, as expected, I find that buzz of the day is SDR or Software Defined Radio.

SDR uses software or firmware to process the radiofrequency signals which was a task done by hardware earlier. Some of the hardware components of previous amateur radio frequency transceiver were mixers, filters, amplifiers, modulators and demodulators. To avoid problems of selectivity multiple band pass filters are used at the front end while receiving signals from various bands. In one commercial equipment about which I read, has as many as 15 band pass filters.

Now what is webSDR? WebSDR is an SDR connected to the internet so that multiple users can actually tune it and use it to listen to the frequency of their choice simultaneously. The WebSDRs can be accessed if you know the URL, using a personal computer connected to the internet, without the need for any other software or hardware. There are several WebSDRs out there for amateur and non-amateur bands. I am routinely listening to the WebSDR for Qatar Oscar 100 Geostationary Amateur Radio Satellite.