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README.md

WWVB Observatory

An archive of WWVB data as received by a low-end receiver at my house

The receiver

The receiver consists of a Raspberry Pi 4 connected to a CANADUINO 60kHz Atomic Clock Receiver with MAS6180C receiver IC. It's located in Lincoln, Nebraska, USA, or around 700km east of the transmitter.

The Pi is reasonably well synchronized to GPS time via NTP.

Per the datasheet, the MAS618C receiver introduces a phase shift of 50ms (typical) to 100ms (max) in the demodulated signal.

The log file

Logfiles are split according to the TAI date and hour, so they consist of filenames like 2021/09-01/01.txt.

A typical line reads:

2021-10-13 15:40:59 TAI ####______|_______________|_______________|__########

The first fields give the date, time, and timescale, currently TAI.

The time fields are followed by 50 samples of the amplitude-modulated signal taken during the second (nominally 20ms apart). Each sample is represented by a _ or a #. # represents the full-strength carrier period and _ represents the reduced carrier period.

The period of full-strength carrier shown at the start of the second is an artifact of the phase shift introduced by the MAS618C receiver.

The line also contains "|" symbols which divide the second into 4 portions according to the nominal WWVB bit framing:

  • The time when the carrier is always reduced
  • The time when the carrier is restored for a "0" symbol transmission
  • The time when the carrier is restored for a "1" symbol transmission
  • The time when the carrier is always full-strength

Since the TAI timescale technically continues to advance during a leap second, the author hopes using it allows leap seconds to be correctly observed. However, it is difficult to actually test this.

The upload process

After each log is rotated away, it is committed to git. Later, it will automatically be pushed to github.

Future directions

  • Show historical data on github.io
  • Log analysis for anomalies
  • Live view via website
  • Additional receivers

License

The Python scripts are licensed GPL-3. The logs, if subject to copyright, are licensed CC0.