Thursday, 18 June 2020

Fascinating 50MHz specular reflections

Late this morning, strong transatlantic 6m Es opened up, which showed remarkable, repeating signal bursts over a long period of time. Update: I then heard the same thing with US-only 6m signals 29/06/2020.

The signal bursts in the US signals are almost certainly the result of glancing specular reflections from gravity wave fronts in at least one, and probably two or three Es clouds.

Audacity audio spectrum plot of Es bursts.
Wave and background motion in Es clouds is very fast - tens to hundreds of metres per second.  The very short duration bursts, sounding very much like meteor reflections, are likely to be made even shorter by the multiple reflections that must line up to allow the path to be heard.

NLC can be considered visual manifestations of Es.  Light 'bursts' are seen in the highly reflective regions where sun-cloud-observer path lines up perfectly.  The same happens with the TX-Es-RX path of VHF radio.

Argo visual plot of received FT8 audio of 50MHz signals, arrows showing the obvious pulses.  The brightest pulse on top left appears half way through a FT8 cycle from virtually nowhere, peaking 40dB above background in fractions of a second.

Recording the bursts with Argo allows them to be visualised, and also measured in intensity.  The peaks of the bursts are 40dB enhancements over background (-60dB against a -100dB background).  You will notice, especially in the second recording, a highly unusual 'metallic' quality to the sound.

In a typical Facebook trolling exercise, someone unilaterally dimissied this as anything unusual, asserting it was "meteor or aircraft scatter" - but not venturing to say which.   I have never heard this kind of effect happen over and over again over many hours, even during major meteor showers.  Sporadic bursts, sure, but not of this quality.  The problem with this explanation is that all propagation can periodically come to a stop at 6m, including the bursts.  There is no good reason why sporadic meteor bursts should simultaneously stop in step with general Es.


There's no way it's aicraft scatter, because air traffic is 95% lower than normal at present, and I have never, ever heard aircraft scatter from here at 50MHz even when traffic is normal.
 


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