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126 lines
4.9 KiB
Markdown
126 lines
4.9 KiB
Markdown
<h1>Radio Clock Plugin</h1>
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<h2>Introduction</h2>
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This plugin can be used to receive the time and date as broadcast on Low Frequency (LF) by various transmitters that are tied to atomic clocks:
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* [MSF](https://en.wikipedia.org/wiki/Time_from_NPL_(MSF)) - UK - 60kHz
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* [DCF77](https://en.wikipedia.org/wiki/DCF77) - Germany - 77.5kHz
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* [TDF](https://en.wikipedia.org/wiki/TDF_time_signal) - France - 162kHz
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* [WWVB](https://en.wikipedia.org/wiki/WWVB) - USA - 60kHz
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* [JJY](https://en.wikipedia.org/wiki/JJY) - Japan - 40kHz
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If you'd like other transmitters to be supported, please upload a .sdriq file to SDRangel's [github issue tracker](https://github.com/f4exb/sdrangel/issues).
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Typically, it will take two minutes before the time is able to be displayed (up to one minute to find the minute marker, then another minute to receive the timecode).
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Although the atomic clocks used to transmit the timecode are extremely accurate, propagation, SDR data transfer and demodulation delays limit accuracy of the displayed time to around 1 second.
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<h2>Interface</h2>
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The top and bottom bars of the channel window are described [here](../../../sdrgui/channel/readme.md)
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<h3>1: Channel frequency entry mode</h3>
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Select from one of the following modes to determine how the channel center frequency is calculated:
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* Δf - Specify an offset in Hz from device center frequency.
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* f - Specific a frequency in Hz.
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<h3>2: Channel Frequency</h3>
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Specifies channel center frequency according to frequency entry mode (1):
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* Δf - Offset in Hz from device center frequency.
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* f - Absolute frequency in Hz.
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<h3>3: Channel power</h3>
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Average total power in dB relative to a +/- 1.0 amplitude signal received in the pass band.
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<h3>4: Level meter in dB</h3>
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- top bar (green): average value
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- bottom bar (blue green): instantaneous peak value
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- tip vertical bar (bright green): peak hold value
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<h3>5: BW - RF Bandwidth</h3>
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This specifies the bandwidth of a LPF that is applied to the input signal to limit the RF bandwidth.
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<h3>6: TH - Threshold</h3>
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For MSF, DCF77, WWVB and JJY, specifies the threshold in dB below the average carrier power level that determines a binary 0 or 1.
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<h3>7: Modulation</h3>
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Specifies the modulation and timecode encoding used:
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* MSF - OOK (On-off keying)
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* DCF77 - OOK (On-off keying)
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* TDF - PM (Phase modulation)
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* WWVB - OOK (On-off keying)
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* JJY - OOK (On-off keying)
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<h3>8: Display Time Zone</h3>
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Specifies the time zone used to display the received time. This can be:
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* Broadcast - the time is displayed as broadcast (which is typically the time zone of the country the signal is broadcast from, adjusted for summer time. WWVB broadcasts UTC).
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* Local - the time is converted to the local time (as determined by your operating system's time zone).
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* UTC - the time is converted to Coordinated Universal Time.
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<h3>9: Date</h3>
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Displays the decoded date.
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<h3>10: Time</h3>
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Displays the decoded time, adjusted for the time zone set by (8).
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<h3>11: Status</h3>
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Displays the demodulator status. This can be:
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* Looking for minute marker - Indicated at startup or after signal lost, while looking for the minute marker.
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* Got minute marker - Indicated after finding the minute marker and waiting for the first timecode to be received.
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* OK - Indicates timecodes are being received.
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* Parity error - Indicates a parity error in received timecode.
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The date and time fields are only valid when the status indicates OK.
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If while in the OK state several second markers are not detected, the status will return to Looking for minute marker.
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<h3>12: Daylight Savings</h3>
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Displays the daylight savings state:
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* In effect
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* Not in effect
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* Starting
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* Ending
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For MSF, DCF77 and TDF, starting/ending is indicated one hour before the change. For WWVB it is set for the whole day. Japan does not use daylight savings.
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<h3>Waveforms</h3>
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The scope shows how various variables within the demodulator vary with time. These can be used to help debug operation of the demodulator.
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The signals available include:
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- IQ - IQ data at channel sample rate (1kHz).
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- MagSq - Magnitude squared (power) of received signal after being filtered with a moving average filter.
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- TH - Current threshold, which is moving average of MagSq - TH setting.
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- FM - Output of FM demodulator for TDF demodulator only.
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- Data - Demodulated data. For MSF/DCF77, this data=MagSq>TH.
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- Samp - Indicates when data is sampled (either for the second marker or for a timecode data bit).
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- GotMM - Indicates whether the minute marker has been received. Cleared when synchronization to second marker is lost.
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- GotM - Indicates when a marker is detected. For WWVB only.
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As an example of how this can be used, we can plot the MagSq as X and the calculated TH as Y, which can help to set the value of the
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TH setting to an appropriate level.
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