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 +0.024626 server c0.prv.dvb.s1.ntp.faelix.net peer server c0.prv.gps.s1.ntp.faelix.net peer server l0.prv.dcf.s1.ntp.faelix.net peer server c0.prv.ext.s2.ntp.faelix.net server m0.prv.ext.s2.ntp.faelix.net server vega.cbk.poznan.pl iburst server 127.127.1.0 fudge 127.127.1.0 stratum 14