Portable AM/FM radios use hardware to tune to FM stations between 88 and 108 MHz and also to AM stations.
In Software-Defined Radio (SDR) mainly software is used to tune to radiofrequencies. A 20 € / $20 dongle allows to tune to and measure radiofrequencies between 25 MHz and 1700 MHz (microwaves start at 300 MHz).
Portable AM/FM radios have a tuner that allows, as its name suggests, to «tune to» or to receive FM and AM radio stations. The FM band is between 87.5 or 88 MHz and 108 MHz. The AM band for Europe is between 150 KHz and 26.1 MHz and for North America between 530 and 1710 KHz.
The simplest case for a tuner is an inductor and a capacitor connected in parallel https://en.wikipedia.org/wiki/Tuner_(radio).
When hardware components are replaced by software components, which now define the function of the radio, we refer to Software-Defined Radio, abbreviated as SDR.
Use of the R820T2 tuner chip (25MHz to 1700MHz)
The cheapest Software-Defined Radio is based on a chip (controller) by Realtek, termed RTL2832U (reference:
It is matched to a tuner chip like the R820T2 tuner which receives radiofrequencies from 25MHz to 1700MHz.
There are dongles than can be connected to a USB port and which are extremely cheap, at approximatively 20€ or $20. It is possible to consult the store of https://www.rtl-sdr.com i.e. RTL-SDR STORE or do an online search for the chip. It is suggested to obtain the first item in the list of the RTL-SDR STORE.
The driver that comes with the dongle can be used or popular software can be donwloaded from https://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/.
The most popular piece of software for Windows is SDR# (SDRSharp). A setup guide can be found at this link: https://www.rtl-sdr.com/rtl-sdr-quick-start-guide/
Here is a video for SDR#:
As mentioned in the setup guide and in the video it is important to adjust the RF gain settings ("Configure" button). You must increase the RF gain from its default value of zero in order to receive most signals, but you must not increase the value too much as that will increase noise and intermodulation signals inside the receiver.
References for FM and AM
Figure 1: RTL-SDR software screen
Figure 1 shows an RTL-SDR software screen. A range between approximately 92 MHz and 95 MHz is depicted. By clicking on the 93.5 MHz peak with FM demodulation it is possible to listen to the FM radio station "France Culture" at 93.5 MHz.