The portable radios use hardware to tune to FM stations between 88 and 108 MHz and also AM.
In Software-Defined Radio (SDR) mainly software is used to tune to radiofrequencies. With a $20 dongle you can tune to and measure radiofrequencies between 25 MHz and 1700 MHz (microwaves start at 300 MHz).
The 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 talk about Software-Defined Radio, abbreviated as SDR.
Use 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. You can consult the store of https://www.rtl-sdr.com or do an online search for the chip.
You can use the driver that comes with the dongle or download popular software from rtlsdr.org at this link: 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 increase the value not too much as that will increase noise and intermodulation signals inside the receiver.
References for FM and AM
The picture shows a range between approximately 92 MHz and 95 MHz. By clicking on the 93.5 MHz peak with FM demodulation I can listen to the FM radio station France Culture 93.5 MHz !