In June of 2021, Carl Luezelschwab K9LA gave a presentation to the Madison DX Club titled 'Modes of Propagtion on 6 meters'.
There are plenty of guides and explanations about propagation on the 50 MHz band in books and on websites and they tend to be pretty basic. In this video, K9LA looks at propagation modes in more detail and as expected, things are often not as simple as they seem.
It's very easy to look at long distance contacts on the 50 MHz band and just blindly assume it has to be multi-hop Sporadic-E. As you will see in the video, we should all keep an open mind and accept that it may be due to other propagation modes. This is especially true now as the FT8 digital mode is showing that weak signal paths exist that weren't so obvious in the past with SSB or CW.
The 51 minute video can be seen below...
Some timestamps and items of interest...
00:00 to 02:20 Introduction
02:20 to 04:20 Old 50 MHz radios
Antenna considerations
Solar Cycle 25
References
04:50 to 09:30 Fundamentals of the atmosphere and ionosphere.
It's interesting to note that K9LA questions if PMSE (Polar Mesospheric Summer Echoes) at 85kms above the Earth plays a part in bending radio signals slightly before they reach the higher Sp-E and F2 layers.In the slide for trospheric ducting, there is an error in that it should read 450 metres as opposed to 450 kms. As K9LA observes, tropo ducting at 50 MHz is very unusual in temperate regions.
At 27:30, there are charts suggesting that Sporadic-E may be changing over the years.
At 32:00, Carl suggests that equatorial Sporadic-E may be a significant factor where signals are crossing the equator at local noon.
At 36:00, the video looks at Chordal Hop modes. As the image below shows, there can be a lot more going on than just simple hop Sporadic-E...
45:20 Antenna considerations
46:50 Cycle 25 status
2 comments:
Hmm. Any discussion of PMSE as a propagation mechanism needs to consider the Bragg wavelength, at least in terms of dismissing the reasonable (but still possibly incorrect) assertion that it is not correct for 6m propagation.
The more sensible way to approach this is to say that the mechanisms that force PMSE and summer Es (and NLC) are the same: principally gravity wave breaking. The difference in height between these phenomena is small, and overlaps (considerably). The physical 'surface' for reflection is always charged metallic meteoric debris, with or without ice.
The comments about auroral Es are garbled. Auroral Es (or enhanced propagation following an aurora) does occur, and is distinct from direct auroral scatter. I disagree completely that auroral Es occurs in the position shown; it almost always lags, often by several hours.
It's a nice attempt, but I'm not persuaded that the references he provides were in fact understood. One can sympathise to a degree, because the leading scientists in this field would not claim any of this is fully known.
JE1BMJ called himself the discoverer of multi-hop Es, which was a known radio propagation, and named it SSSP, but nobody accepted it. Whether it is a chordal hop or a reflection in a duct, the phenomenon of "multiple reflections" is the same, and there is no mistaking the generic term multi-hop.
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