This is the board which you can use to solder the HKW581 chip add some components and it just runs on the arduino with few STD components.
You can work with most DCF77 chipsets but i recommend this one from HKW http://www.hkw-shop.de/Empfangstechnik-AM/Aktivantennen/Aktivantenne-S-DCFn.html
You can see the pin settings in the picture below. The LED is hardwired so that you can instantly see if the signal coming into the receiver is stable. THis can be a great help in the alignment proces especially if you are living in an area far away from mainflingen where the transmitter is in Germany.
You can simply plug this into the 3.5 mm audio jack socket which you can also buy from my site.
You do not need the adapter board if you buy this one. Please note that this is the naked PCB and no components are included.
You can find a detailed description and the needed software here.