Robbie, EI2IP reports that there was an unusual opening on the 28 MHz band on the 21st of March 2024. At the moment, the 28 MHz band closes here in Ireland at about 21:00 UTC which is about two hours after sunset.
Robbie reports working FM4LV in Martinique in the Caribbean on the 28 MHz (10m) band at around 00:49 UTC on the 21st of March which is about six hours after sunset. This is very unusual and raises the question what was the propagation mode?
The general expectation is that all F2 layer propagation should have disappeared six hours after sunset.
FM4LV was on FT8 and there were loads of stations to the west of him reporting his signal. None of these are of interest as they're just the usual F2. These are the stations to the east that heard FM4LV after 00:00 UTC...
EA7DZ 10m FT8 6100 km 00:55:14 (Spain)
CN/TANGER 10m FT8 5938 km 00:50:00 (Morocco)
EI2IP 10m FT8 6217 km 00:49:11 (Ireland)
EA8RH 10m FT8 4791 km 00:39:42 (Canary Islands)
EA8AXB 10m FT8 4920 km 00:23:14
EB7FBJ 10m FT8 6091 km 00:15:11
The paths to the far south of Spain, Morocco & the Canary Islands are well to the south and are much more likely to have propagation at 28 MHz, even well after dark. The question is how was there a path to EI2IP in Ireland at 52 deg north?
That brings us to the good old dependable Sporadic-E.
Q. How did the F2 layer propagation reach that far north? Answer - An extra hop provided by Sporadic-E.
Q. How is any unusual path possible? Answer - Sporadic-E.
Q. "The propagation chapter in my ARRL handbook doesn't explain how I made a contact?" Answer - Sporadic-E.
Q. Why did my coffee go cold? Answer - Sporadic-E.
OK, I lied about the last one but the point being is that we seem to perhaps use Sporadic-E as an explanation a bit too often. In this case, the opening was at about 1am in the morning in March, not a time noted for Sporadic-E as the Sporadic-E season doesn't start properly until mid-April and it's usually during the daylight hours.
The map above shows the parts of the earth in sunlight and shadow around the time of the opening.
For EI2IP, it's in the middle of the night and six hours after sunset. For FM4PV, it was about two and a half hours after sunset.
When I took a screen grab of this image, I couldn't help notice that the moon was almost directly above Martinique which got me thinking. If the moon is visible to both stations then signals must be reflected off the surface of the moon even at 28 MHz?
In this case, I think the combined antenna gain was probably too low for moon bounce and the answer is probably that the signals came off a layer in the ionosphere. As for the exact propagation mechanism?
When I looked at an online propagation map, it suggested that the path was impossible at that time of day so it's a bit of a mystery.
