Time Signal Decoder

For some signal detection tasks, the program may require a very accurate time. There are some time references in the longwave part of the radio spectrum, which you may receive and decode with Spectrum Lab.

Some decodable time signal transmitters are:

• MSF from Rugby (United Kingdom) on 60.0 kHz
• HBG from Prangins (Switzerland) on 75.0 kHz
• DCF77 from Mainflingen (Germany) on 77.5 kHz

To decode the time signal transmitted by one of these stations, tune your radio to its frequency (switch the receiver to CW mode) and listen to the audio (audio frequency should be 650 to 800 Hz). If you hear a carrier which is interrupted every second by a shorter or longer "gap", connect the receiver to the soundcard. Check the audio level with SpecLab's oscilloscope if required.

Next, start the Time Signal Decoder by opening it's control window (from SpecLab's main menu (View/Windows..Time Signal Decoder). A window like the one shown above should appear.

Wait for at least two minutes until you get a valid display of the decoded time and date. The decoder should then display which of the transmitters is being received (DCF or MSF).

"RESET"-Button

forces the decoder to start a completely new decoding cycle (useful after you changed your receiver's frequency !).

"Set Clock"-Button

allows you to set your PC's clock accurately to the decoded time (only use this after you verified that the signal is ok!).

"Decoded" and "Date"

are the current values from the time signal decoder. Note that the hour may differ from your local time zone.

"PC clock"

is the current time from the PC's internal clock. It is shown here so you can verify proper decoding.

"Deviation"

is the difference between your PC clock and the decoded time signal. After clicking "Set Clock" it should show a constantly low value (less than 100 milliseconds).

If you also activate SpecLab's (preliminary) digimode decoder while the time signal decoder is active, you can see the received data bits in the RECEIVE window. A new data bit will be received every second, the minute synchronization marker will be displayed as a letter 'm' in a new line of the RECEIVE window. The meaning of the received data bits depends on the station. The data format of MSF is completely different from DCF77 + HBG. Details could be found at these sites (in December 2000):

http://www.npl.co.uk/npl/ctm/msf.html

http://www.prog-link.com/dcf77/dcf77-contents.html

http://w4u.eexi.gr/~sv1xv/lw.htm (LF-Info by Costas, SV1XV)