Here is the full list of all 23 Alt-Frequencies achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Have Sadie be broadcasted on another frequency.
Disturb Fred with the voice of his manager Margot.
Shame Ennis with his past.
You stayed in the time loop.
Complete chapter five.
You left the time loop.
Spoil Ennis' new song.
Reveal the new voice of resistance.
Complete chapter four part two.
Confuse Ennis with the nature of your offer.
Learn about the Landing Plane.
You sent Jenni's list.
Complete chapter four part one.
You sent Kaya's list.
You sent the RMB-1 scoop to News One.
You sent the RMB-1 scoop to Talk radio.
Complete chapter three.
You sent the RMB-1 scoop to Fresh FM.
Complete chapter two.
Suggest a cure for Michelle's flu.
Complete chapter one.
Ask A. None a relevant (???) question.
Complete the tutorial.