Simulcasting I'm guessing. There are several sites broadcasting this system, not just at the ECC.
You must be in an elevated part of the county and receive strong signals from several sites.
I can see the ECC. I can receive Loudoun fine, though when at home I leave the antenna off.
I don't have the slightest signal for DC FD, wish I did though, only get MPD.
Try using the attenuation or removing the antenna.