Atomic Time Receiver

We have seen them all, the small convenient LCD clocks that run extremely accurate because they receive exact time information from special long wave radio transmitters. There are different systems around the world, using different frequencies and different protocols.

A few systems that I know of:

These transmitters all use AM modulation and transmit a telegram with time and date information. Each telegram is one minute in lenght. A telegram consists of 60 or 59 pulses, one per second. Each pulse presents one logical bit of the information. The length of the bit tells whether it's a '0' or a '1'. A decoder is needed to collects these bits until a complete telegram is received. The decoder is implemented in software and resides inside the PIC/AVR controller.

The protocols used by the various transmitters around the globe are not the same. Each protocol requires a decoder that understands it. All nixie clocks at least understand the DCF77 protocol and some of the latest versions also understand WWVB. The software automatically recognizes the signal and passes the signal to the correct decoder. 

At the moment I can offer the DCF77 decoder and the WWVB decoder. The DCF77 decoding software was developed quite some time ago. Since I can receive that signal here, it was not too difficult to develop. Many clock builders use it, and the software is very good in doing it's job. It uses all kinds of smart digital filtering and error checking to ensure a correct decoding result. The WWVB decoding has been added in january 2005. Although largely based on the DCF77 software, this was a lot harder to develop because I can not receive the actual signal here in the Netherlands. Special thanks go to Rex and Mike (both living in the US) for testing the first beta versions. There were a few minor issues, but these have been solved now. From april 2005 the WWVB software has proven to be rock solid and is available for the binary clock, the 1 tube clock and for the 6 tube clocks. 

The receiver and antenna need to be placed away from the clock at a minimal distance of 1 meter. If you put the receiver closer to the clock, it may pick up interference from the multiplexing drive and HV generator. The antenna should be kept horizontal and for best results the long side facing to Frankfurt in Germany (DCF77), or to Boulder in Colorado (WWVB). Also keep the extremely sensitive receiver away from other sources of electrical noise, such as PC's and switched mode power supplies. 

Basically, the only thing you need is a receiver and antenna and a piece of wire. I have prepared an enclosure kit, which you can order along with the receiver of your choice. Instructions how to connect the receiver module can be found in the document below.

Files for Enclosure Kit

Last updated 29 Sep 2006