The reporter in an unidentified type aircraft experienced an NMAC with another aircraft entering the same pattern at FDK on the 45 to downwind just in front of him. Although both aircraft had PCAS devices aboard they provided no warning.

Narrative

When entering the pattern at FDK I radioed at 10 miles north; five miles out on the 45 to left downwind Runway 30; three miles out on the 45 to left downwind Runway 30; and upon entering left downwind. Between my 5 mile and 3 mile call a Cirrus called '2 miles out on 45 to downwind FDK.' He was not found visually or on my PCAS (Portable Collision Avoidance System). As soon as I turned to left downwind the Cirrus entered downwind approximately 300 FT in front of my aircraft at 1300 FT. I called I would follow the aircraft that had just entered the pattern immediately in front of me. The Cirrus did not respond; but did make calls on left base; final; and upon exiting the runway. I slowed and was able to land normally after the Cirrus turned off the runway. After landing I went to the Cirrus pilot and told him he had cut me off in the pattern. He stated that was impossible because he has a PCAS and my aircraft did not appear on his display. My conclusion is this pilot was not listening to radio for traffic before entering the pattern; and was flying the pattern head-down looking at his PCAS. Further; he must not understand that PCAS requires radar to query the transponders around it; and that radar hits while in the pattern are infrequent. My understanding is that FDK is the second-busiest airport in Maryland; and is scheduled to get a control tower. Tower operations at FDK cannot begin soon enough!