This is a basic MSF60 receiver for GNU Radio, containing:

1. signal demodulation and detection of the MSF60 OOK signal with an SDR using GNU Radio (and Python modules)
2. a simple live decoder of the received OOK bits provided by the GNU Radio MSF60 receiver

MSF60 (from the National Physics Laboratory (NPL) is one of the UK time signals in Anthorn, Cumbria, UK.)

The flowgraphs are provided in the examples folder:

• MSF60_Receiver.grc
  • for both SDR reception and for SDR simulation
• MSF60_Channel.grc
  • only for simulation
• MSF60_Transmitter
  • only for simulation

Supplementary tools are provided in the python folder:

• DecodeMSF60.py decodes the received OOK bits from a specified ZMQ server upon receiving them. It shows the current time, date, weekday, etc. at each new minute.

The MSF60 receiver was tested with:

• gnuradio & GNU Radio Companion 3.10.1.1 (Linux)
• Radioconda 2023.02.24 & gnuradio & GNU Radio Companion 3.10.5.1 (Windows)
• Python 3.10.6
  • PyQt5 5.15.7
  • pyzmq 23.1.0
  • gnuradio-osmosdr 0.2.0
• An SDR receiver capable of receiving in the range of at least 1 kHz - 1 MHz, e.g. an Airspy Discovery HF+ is configured and used for this project.
• An antenna that provides a sufficiently clear MSF60 signal, e.g. a simple YouLoop loop antenna was used for this project. Indoor reception should probably be possible if you are close enough (<1000 km) to the MSF60 transmitter in Anthorn, UK. You should mount the antenna close to a window or outside.
• The user might also need some antenna cables and adapters to connect the SDR with the antenna.
• This project has been successfully tested in:
  • Ubuntu 22.04.2 LTS (recommended)
  • Windows 11

• Open the following 3 flowcharts (MSF60_Transmitter.grc, MSF60_Channel.grc, MSF60_Receiver.grc) in GNU Radio Companion.
• Generate the Python files with the "Generate the flowgraph"-button.
• Open 4 separate terminals (e.g.: T1, T2, T3, T4).
  • Change to your cloned repository in all 4 terminals.
• T1: Go to /examples/MSF60_Transmitter/
• Run transmitter with: python3 MSF60_Transmitter.py
  • It should be run in the 1st step.
  • A GUI should appear.
  • The terminal should provide additional information continuously.
• T2: Go to /examples/MSF60_Channel/
• Run Channel with: python3 MSF60_Channel.py
  • It should be run in the 2nd step.
  • A GUI should appear.
• T3: Go to /examples/MSF60_Receiver/
• Run Receiver with: python3 MSF60_Receiver.py
  • It should be run in the 3rd step.
  • A GUI should appear.
• T4: (compare above) go to /python/
• Run the decoder with: python3 DecodeMSF60.py
  • It should be run in the 4th step.
  • The terminal should provide received bits continuously, and a time & date message each minute.

Details on the parameters of the receiver are described further below.

• Set up your SDR with your computer.

• Ensure that the raw MSF60 signal reception at 60 kHz is good enough, e.g. using gqrx, SDR# or another signal analysis tool.

• To start the MSF60 receiver, open the flowchart in /examples/MSF60_Receiver/MSF60_Receiver.grc with GNU Radio Companion

  • Press run button.
  • Set the Recv Gain slider values in the MSF60 GUI so that the amplitude of BB signal is centered roughly around the value 9000.
  • Adjust the Threshold slider values, if needed.
  • The slider LP width and LP cut-off can be used to change the dense low-pass filter, but these values should rather be kept as they are.
  • After parameter adjustment, the GNU Radio Companion debug console should show a debug message each second with either '00', '01', '11, '10, or '2' (for new minute).

• Next, open a terminal or Powershell.

  • Change to your cloned repository.
  • Run DecodeMSF60 with python3 ./python/decoder/DecodeMSF60.py.
  • The terminal should show the received bits together with a sequence of indices.
  • after approximately 2 minutes, DecodeMSF60 should be synchronized with the transmitter. It should provide the current time, date, etc. each minute.
  • NOTE: sometimes a bit can not be decoded correctly, e.g. due to bad reception. Then the current frame of the minute is corrupted and both the decoder and detector will produce error messages and will attempt to re-synchronize.

• ⚠️ Please note that the MSF60 transmitter in Anthorn, UK, is sometimes offline due to maintenance work, cf. https://www.npl.co.uk/msf-signal for the precise schedule.
• This project has not been tested with other SDR receivers, yet.
• This project has not been tested with a receiver setup using a sound card.
• This project has not been tested with other antennas (e.g. a ferrite antenna).
• A Low Noise Amplifier (LNA) is not needed.
• Even a single lost bit during reception causes the synchronization of a full minute to fail. Additional resilience of the decoder has not been implemented yet.
• Bits 01-16 carrying the difference (DUT1) between atomic and astronomical time are currently ignored by the decoder.
• The project provides the decoded MSF60 signal more or less in real-time, but it is probably not accurate in terms of milliseconds.