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. Even more accurate timing than with a longwave time signal is possible with a GPS receiver with sync output ('PPS'). Thus, the time signal decoder described in this document has become slightly outdated.

Some decodeable time signal transmitters are:

• MSF / Rugby (United Kingdom) on 60.0 kHz
• HBG from Prangins (Switzerland) on 75.0 kHz (went QRT, only of 'historic' use)
• DCF77 from Mainflingen (Germany) on 77.5 kHz
• ( no decoder for WWVB .. it was "far out of reach" for the author,
  and very unfortunately on the same frequency as MSF / Rugby )

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.
Alternatively, if your soundcard runs at 192 kSamples/second, you can connect an antenna directly to the soundcard's input (without a receiver), and in this case set 'f_center' on the 'Config' tab to 60000 or 77500 Hz.

Next, start the Time Signal Decoder by opening it's control window (from SpecLab's main menu (Components..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). It's not necessary to select the transmitter manually.

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!).
This feature didn't work on Windows 7 without running SL 'as administrator'.

Decoded and Date (display)

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

PC clock (display)

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

Deviation (display)

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 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 October 2020):

www.npl.co.uk/msf-signal

www.ptb.de/cms/ptb/fachabteilungen/abt4/fb-44/ag-442/verbreitung-der-gesetzlichen-zeit/dcf77.html

Interpreter functions for the Time Signal Decoder

The following functions in SL's command interpreter can be used to access the time signal decoder:

time_dec.time

Returns the last decoded date and time in Unix format (seconds since 1970-01-01 00:00:00 UTC).
Takes the 'age' of the decode into account, thus there is a fractional part (from 0 to 0.999 seconds).