I've found that antenna orientation matters, even in the Netherlands which is much closer to DCF77 (concrete house).
Or one can use a PC to transmit the DCF77 signal locally (it could be illegal) to a clock using a pair of headphones, I've seen at least a couple of examples but never tried them.
Edit: found the photo http://forums.watchuseek.com/f17/possible-method-improve-ato...
You can find more details in the second page of this datasheet
https://www.gemischtwaren-haendler.de/shopdateien/3942_1.pdf