You must to get this achievement before getting the third signal
When you can control the robot walk all the way to the right and you'll find some radio towers and a lone radio tower, the biggest one. You should hear a "bzzz". Stand at this tower for some minutes and you'll get the achievement.
Fun fact:
UVB-76, also known as '"the Buzzer", is the nickname given by radio listeners to a shortwave radio station that broadcasts on the frequency 4625 kHz
.
https://en.wikipedia.org/wiki/UVB-76