firmware-ralink software package provides virtual package provided by firmware-misc-nonfree, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install firmware-ralink
firmware-ralink is installed in your system.
Make ensure the firmware-ralink package were installed using the commands given below,
$ sudo dpkg-query -l | grep firmware-ralink*
You will get with firmware-ralink package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Virtual packages |
| Package | firmware-ralink |
| Version | |
| Description | virtual package provided by firmware-misc-nonfree |
| Sub Section | Virtual |