Recently I noticed that local to KIAD I was receiving lots of codes in the 7d4xxx range and displaying with lowercase letters in PlanePlotter. They even have ADS-B out and plot on the map throughout MD and northern VA. At the same time the code FAAFFC with ID XLS88 started showing up with ADS-B locating it at the ITT Exelis facility in Herndon. Sometimes they also broadcast the hex BADDA55 from the same site. So it seems they're transmitting test data. Through ADSBx I've noticed a similar thing happening in the Los Angeles area lately. These codes are in the 298xxx range. LAX has a bunch of 318xxx codes showing, no idea if those are legit ground stations or test data.
