Galaxy News Radio is the radio station located within the DC wastelands, the location which your father visited at one time. The DJ of the radio, Three Dog, has spoken with your father recently before heading on.
Three Dog won't immediately give information about the father since he wants to be certain that you are going for the "good fight". As you could tell, the radio signal from Galaxy News Radio isn't that strong, and it was because a Super Mutant thought the antenna was a bullseye.
He asks you to retrieve the satellite dish from the Museum of Technology (located near the Washington monument.) The dish in question is located on one of the Virgo satellites, and is extremely rare now since the factory that produced that type of equipment was leveled.
Museum of Technology
The museum of technology provides a demonstration of the various pieces of equipment seen in the game, and as with all places in DC, is infested with Super mutants.
You can access the satellite room by going through the Vault Tek demonstration on the second floor.
With the antenna dish in hand, you can open the Washington Monument with the password given by Three Dog. Take the elevator to the top, and use the equipment to attach the antenna. Once done, the radio quality improves significantly; return to Three Dog to report on your progress.
When you complete the task for Three Dog, he will reveal the next known location of your father, Rivet City. However, if you already spoken to Dr. Li, he will instead give you to a key to a weapon cache located within Hamilton's Hideaway.