For more information see the new docmentation [688 KB] .
We use a small DCF77 receiver by Conrad (DCF EMPFAENGERPLATINE
Artikel-Nr.: 641138 - WE) That is about 10 Euro.

The DCF77 radio controlled clocks receives the official time of the Federal Republic of Germany from Physikalisch-Technischen Bundesanstalt (PTB) in Braunschweig and transmit it to computers and systems via various interfaces. The radio synchronisation of the DCF77 transmitter in Mainflingen (50 01 N, 9 00 0) reaches a long term accuracy of the PTB-calibration standard of 1 x 10 E-13 per week or less than 1 second in 300,000 years.

This station transmits continuously, except for short interruptions due to technical faults or maintenance. Longer breaks may be experienced during thunderstorms attaching the location of the transmitter.

Time Signals Except of the second marker 59, the carrier is modulated by second markers each minute signifying that the next marker will be the minute one. At the beginning of each second the signal amplitude is reduced to 25% for 100 ms or 200ms. The start of the decrease of the signal amplitude marks the exact beginning of the second. The second markers are phase- synchronous with the DCF77-signal. In general: the inaccuracy of the received DCF77 times ignal is large compared to the emitted time signal.

The reception depends largely on the limited wave band of the time signal transmitter and other natural interferences. At a distance of some 100 kilometres, a time signal uncertainty of less than 0.1 ms is achievable. (Text by Hopf Electronic)

How the DCF77 software version 5.6 works

At power up, it shows the software version blink in the hour digits.
If no valid DCF signal has been received for 3 minutes, the clock display will be turned off. This is done to warn that a bad antenna placement and to minimize radio noise, that the tubes might produce. This will in some cases help if the antenna is placed too close to the Nixie clock.
The display will stay off until: a good DCF is received or the SET button is pressed. If the SET button is pressed,
the clock will tell the time it has been running for since power up.
The clock will always seek for correct DCF pulses and if valid time information has been received, it will set the clock. Every time the clock is set to the correct DCF77 time, the LED D31 will change its state.

How the quality meter works:
D30 is the dual colour LED. It works as a signal quality meter. It is very fast reacting every second. It indicates how close the pulses are to the correct pulse width. A correct pulse width is 100ms or 200ms. Green blinks if the pulses are correct pulse +- 10ms. Orange will blink if correct pulse time +-20ms. Red blinks if correct pulse width +- 30ms. If the pulses are more than 40ms away from correct time the signal will be marked as bad. That means it is actually possible (in theory) to set the clock to correct time if only red blinks.

Due to this fast reacting quality signal meter it has never been so easy and so much fun receiving correct DCF77 signals.

If a bad DCF signal is received for 24 hours or more, the red LED D31 will change state every second. This is to warn the user that the clock might be off time a few sec or maybe more depending of how many days / weeks this have been going on. The warning is off again if good DCF is received.

Also the Nixie display will be turned off at 4:00 in the morning and back again at 5:00 only IF bad DCF77 is received for 24hr or more. This is to help users with maybe noise problems or weak radio signals during the day when most computers and TV-sets are on.

If D30 is blinking green and the D31 changes state almost every minute you have nothing to worry about and your clock will be super accurate.

12-24 hour selection
Hold down the UP/DIM button for 3 sec to change from 12 hr to 24 hr mode and back. The EPROM will keep the setting for 12 or 24 hours mode even if the clock has been powered off.

No leading zero
If you want to blank the leading zero, then just cut the connection to the first hr "zero sign".

Dimming
The UP/DIM button changes the 4 dim levels when clock is in normal.