I found another discussion ads-b-flight-tracking-f21/978-mhz-uat-in-the-us-t18256.html . Seems that there are a few attempts to build the 978MHz decoder, but no an easily installable package.
My dump1090 plot page usually have 1 to 2 ratio of the planes with position vs planes without position (i.e 5 planes with position and 10 without position). The planes without position often have squawk, flight number, altitude and message counter in thousands. Judging by the flight number, some of the planes are airliners (US Airways for example) yet they do not report position. Is it possible that the position of those planes is transmitted via ADS-B UAT?