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Man Pages

Manual Reference Pages  -  DCF77RX (1)


dcf77rx - soundcard DCF77 (and HBG) beacon receiver




dcf77rx [-a audio device] [-s] [-n] [-v verboselevel (1 or 2)] [-g] [-p] [-l] [-u] [-t]


dcf77rx is a soundcard demodulator for time reference signals transmitted by the transmitters DCF77 and HBG on LF frequencies. The program expects the transmitter signal downconverted to an audio passband frequency of 1kHz by an LSB or USB receiver. A circuit for home-brewing such a transverter is included in the docs of the hf package.

The decoded time information is used to derive correction factors for the sampling rate, the gettimeofday clock and to measure the exact CPU clock frequency. These clock sources are used for calibration in my AMTOR/Pactor1 package (hf) as reference clocks. This program is part of the package.


-a specify the path to the sound driver (default: /dev/dsp on Linux, /dev/audio on Solaris).

-s use standard input instead of audio input. Format is 8kHz 16bit words 1 channel in the endianness of the CPU.

-n do not use the ‘mmap()‘ way of approaching the soundcard, which means, do not read directly from the soundcard dma buffer. Some soundcards do not support mmap mode. This option is experimental, it is not yet tested how good the results will be!

-v Set the verbosity level (1 or 2, default 0). The higher the number, the more debugging information is written to standard error. At first use, try level 2 to get familiar with how it works.

-g HBG mode.

-p DCF77 phase mode. DCF77 transmits the time information amplitude modulated and phase modulated with a pseudorandom code. This option uses the latter to decode the time. This is strongly recommended, as the PN code is more robust and allows much more exact determination of the second pulses.

-l Receiver uses LSB (lower sideband) mode.

-u Receiver uses USB (upper sideband) mode.

-t Set the system time to the received MEZ btw MESZ (CET btw CEST) from DCF77.


In DCF77 BPSK PN mode, due to the small number of searchers and therefore low system load, the receiver requires around 15sec to acquire the second clock.

Due to the nature of the amplitude modulated transmissions from HBG and DCF77, the receiver is quite sensitive to noise and preturbances.

The receiver requires more than one minute to acquire time, due to the nature of the transmissions. To calculate correction factors, the program should run at least 15 minutes. Tune the receiver patiently, first so that the carrier frequency offset is smaller than about 1 Hz (you see it with -v 2) and then the second ticks should be catched as secondly as possible, you can see this by the rotating rod or also as text with -v 2. Best calibration time is daytime. Do not believe the first output, see if an exact value comes repeatedly, because errors are possible due to noise!


Hans-Guenter DF4OX/DL0PTB sent me printed documentation about the DCF77 transmission format which helped me a lot.


Thomas Sailer, HB9JNX/AE4WA, and some small adds by G´┐Żnther Montag, dl4mge@darc.d
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HB9JNX DCF77RX (1) DCF77 utilities

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