Be careful with that receiver as it operates at 77? KHz (in the US it is 60 KHZ, WWVB) and it is an AM receiver and although the antenna is more magnetic that electrostatic ( A Ferrite loop antenna) the receiver is still subject to radiated noise from the Arduino's clock. I personally would shield everything but the antenna in a metal container and make certain that my power supply to the receiver was very clean. I live in Southern California and it is about 1000 miles to the antenna for the DCS 60 service here because of that there is almost no reliable coverage here during the daytime just at dawn and dusk. For 10 12 dollars more you can buy a GPS receiver and it is much easier to interface than the DCF77 service is. They aren't the best indoors but both of mine work well enough to receive the time data. I might not always (30% of the time) get position data that is accurate but the time always works as you only need one or two sat's for time data to be valid. you are fairly close to the DCS77 service and it should be no problem, If you do have issues make sure that you have the bigger of the two antenna's that CMS sells for that receiver as it is more sensitive and use a small co-axial cable to connect the antenna (RG-174) so you can "remote" the antenna by a meter or so to remove it from the immediate radiated noise from the Arduino.
Doc