cutesdr software package provides simple demodulation and spectrum display program, 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 cutesdr
cutesdr is installed in your system.
Make ensure the cutesdr package were installed using the commands given below,
$ sudo dpkg-query -l | grep cutesdr *
You will get with cutesdr package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Ham Radio |
| Package | cutesdr |
| Version | 1.13.42-2 |
| Description | simple demodulation and spectrum display program |
| Sub Section | hamradio |