c0.prv.dcf.s1 uses a Conrad DCF77 receiver module (with antenna) built using Jonathan Buzzard's NTP radio clock instructions. ntpd uses the shared memory refclock driver to receive the decoded signal from radioclkd.
server 127.127.28.0 fudge 127.127.28.0 refid DCF fudge 127.127.28.0 time1 +0.000000 server c0.prv.dcf.s1.ntp.faelix.net peer server c0.prv.dvb.s1.ntp.faelix.net peer server c0.prv.gps.s1.ntp.faelix.net peer server c0.prv.ext.s2.ntp.faelix.net server g0.prv.ext.s2.ntp.faelix.net server l0.prv.ext.s2.ntp.faelix.net server 127.127.1.0 fudge 127.127.1.0 stratum 12