Dawn DopplerΒΆ

Title: Example of Dawn Doppler from WWV at 5 MHz

Contributed by: Gwyn Griffiths G3ZIL

Reviewed by:

Receiving Station Location: KD7EFG Northern Utah SDR site near Corrine, Utah DN31uo

Receiving Station Details WSPRDaemon Grape SDR receiver.

Feature Description Figure1_5MHz_DN31uo

A. By choosing a receiving station reasonably close to WWV - 617 km - and a low HF frequency - 5 MHz - we have the conditions for the band to remain open all night. This means the Doppler spectrogram shows the expected night time near-zero Doppler shift until about 1300 UTC. There follows a rise in positive Doppler - the phase path length decreasing - as the height of reflection descends due to increasing ionisation as the sun rises. The Doppler shift (speed of descent) reaches a maximum, then reduces to near zero.

At a higher frequency the band may not be open at night and we may only see part of the Dawn Doppler trace, e.g. from just at, or just after, the peak positive Doppler.

There are other features in the spectrogram which other descriptions in this guide will help you spot and understand.