Curious enhancement in the DGPS band this morning

[ChrisSmolinski]

This is very curious. i accidentally left my SDR recording the DGPS band all day today. I went back to check the recordings to see what was there. Just after 1500z, there was a short period where a bunch of stations came in:

[ChrisSmolinski]

I checked the SDR recording waterfall, and it seems this was a window with reduced background noise levels. Now to track down the offending QRM source...

[jFarley]

Looking at the image around 1500z and seeing what was being reported, I'd have to say that those are very likely real reports and captures.

LW propagation is dominated to a great degree by conditions in the D layer of the ionosphere, and here there is a continuous dance between its ability to refract LF and its ability to absorb LF.  This can lead to some very surprising propagation.

Long haul DX at LF is indeed mainly a night time phenomenon.  Here a fully dark path between TX and RX is required, and the open window for reception of distant stations usually starts a couple of hours after the path has gone dark, and lasts until sunrise approximately.  I think most DXers would understand and agree with this.

During daylight hours, one can generally expect to hear only locals, and for typical domestic LF NDB power levels the range is generally 150 to 200 miles.  Again, no surprise here.  Here in Illinois, I generally hear NDBs from Iowa, Indiana, Wisconsin, Michigan, and Ohio with regularity.

A very surprising thing happens around local noon at the RX, however.  There appears to be a temporary change in the balance between the refractive and absorptive properties of the ionosphere which can dramatically extend the range of NDBs that can be heard.  Around 1800z plus or minus I have heard NDBs out to Nebraska, Texas, Pennsylvania, Quebec, and upper Ontario.  This is not something that would be expected, but is a phenomena with which most NDB DXers are familiar.  Taking a nooner bandscan is a very common thing.

I have seen some extreme loggings of LF NDBs which would really surprise most.  One which really made me do a double take was a log of CB 245 kHz- Cambridge Bay, Nunavut - last January.  The DXer was in Texas, and the range to Cambridge Bay was about 2600 miles.  IIRC, he had to use audio power averaging software over a couple minute capture to extract the call, but still...

Your caps around 1500z would be a couple of hours before local noon if I did my math correctly, but would still be believable.  The period between local SR and noon can have some very dynamic propagation conditions.

It makes me wonder.  I think Europe has more NAVTEX stations than DGPS, and I wonder if you could cap any TA NAVTEX in the morning period given your location?

[Looking-Glass]

The morning of the 18th September produced an outstanding opening on the NDB band in the period 1530-1700z with a number of Western Australian beacons very audible here (2,000 to 3,700kms).  I scored one new one out of it with KG Kalgoorlie WA on 287KHz 319-419 report for 2,722kms.  Other than that openings/conditions have been fair to poor. 

Would be interesting to know why the sudden path to Western Australia, beacons in South Australia were abnormally strong with LEC Leigh Creek on 287KHz for 1,216kms just a scrap under 10dB over nine report.  The path east to New Zealand was void so it was a western opening. 

Some good work there again Farley...

[ChrisSmolinski]

Thanks, jFarley. I will try to run some daytime recordings, to see if I can better pin down exactly what is happening. I think there is some sort of local QRM source as well, and I could certainly be seeing a combination of QRM appearing and disappearing, as well as real propagation. I agree that these decodes are likely real.

As Murphy would have it, I am also suffering from the SDR-14 randomly leaving run mode. I am not sure if it is the SDR-14 itself, or the server app I run that makes it appear as a networked SDR, so I can use it with SdrDx. As a result, I did not get my usual overnight recording run last night, except for a few bits and pieces when I would manually start it recording again. I have the AFEDRI running now, and will try using that today and overnight (minus possibly moving it and the beverage to Europirate service this evening, if 48m conditions are as good as last night).