A DCF77 option sets the clock(s) from the Atomic Time Transmitter in Frankfurt Germany.
The reciever is a small ready built module (35 x 19 mm) and available from Conrad.
I mounted the DCF77 module (with hot glue) in a small box, also from Conrad.

Conrad part numbers:
522244-20 Module Box (54 x 37 x 21 mm)
641138-62 DCF 77 Receiver Module

Screened two core cable is used to connect the module to the clock PCB.

Nice and clean

The next photo is interesting!
It shows the 1N14 clock, the CD81 clock, a radio alarm clock, and a Squeezebox together, and all synchronised.
The Sqeezebox is displaying time from an internet NTP server, the other 3 clocks are displaying DCF77 decoded time.

Four clocks, and all in perfect sync!