Software Defined Radio, or SDR, is a cheap and exciting entry point into amateur radio. As the name suggests, SDR allows for easy reconfiguration of a radio emitter/receiver. Therefore, instead of using various components to compose a unique radio configuration – which is an expensive approach with a long time to market –, we use a general-purpose processor to perform the heavy lifting such as signal demodulation, digital signal processing, etc. With abundant and omnipresent CPU power, SDR could only gain traction and become widely available. Since CPU power is available in computers, they are a perfect host for an SDR. When Realtek Semiconductor released the RTL2832/U demodulators with FM/DAB/DAB+ radio support, it was quickly adopted to build SDR USB dongles very affordably. They can be searched using the RTL-SDR keyword (RTL standing for Realtek) and can be as cheap as $20. Of course, these dongles are not capable of transmitting, but you can listen a lot, starting with FM radio stations.
I picked a Nooelec NESDR SMArt v4 USB dongle, which uses the RTL2832 chip allowing a frequency range between 25MHz – 1750MHz. The SMA female connector receives an antenna, and the USB connector plugs into a PC. Windows recognize the dongle as a Bulk-In interface (USB). Because it is an SDR, it provides the demodulated signal to the PC, and a radio software must process it to generate the signals of interest, mostly audio sent to a sound card – but could be decoded digital transmissions via radio, but that’s out of these device’s scope. In my case, I’ve tested HDSDR 2.80 by Mike Ladd and SDR# 1.0.0.1732 by Airspy. Both worked well, once the right driver was installed – overwriting the Microsoft driver using zadig-2.5, and adding the ExtIO_RTL2832.dll manually into the HDSDR installation folder. Et voila!
