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Greyline LW DX?

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#1
Received 90 NDBs this morning during a session lasting about 1 1/2 hrs just before sunrise. Reception was mostly north-south along what would have been the greyline. Just wondering if others have had similar experience with apparently greyline propagation or is it just coincidence?
 
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#2
Hmmm...:) Interesting. I googled and found nothing concrete - they all talk about HF greyline prop but nothing about LW. At sunrise/set the D layer is dissappearing but the higher F2 is there which is why HF works but I think that LW frequencies go straight through at night. Most LW prop is via the ground wave which will go for 2000km under good conditions and also a bit of ducting given the right circumstances too.

Many years ago when I was a radio op in the Merchant Navy we were leaving the Persian Gulf passing through the Straits of Hormuz in the very early morning just before dawn. The old man had got me up to send the departure message to head office in London but I thought that I wouldn't get through until we were further out to sea. The receivers were all on of course and suddenly I heard Niton Radio call CQ on 500kHz with his traffic list to be sent on 464kHz. (Niton is on the Isle of Wight on the south coast of England.) I quickly tuned up on my working frequency of 468kHz and as soon as he finished his traffic list I gave him a quick call more in hope than anything - I only had 100watts on CW! Much to my surprise he came straight back! I sent my message and he asked me for a TR (a Traffic Route message, so that the UK Post Office know to send messages to the right coast station) - he was quite surprised when I told him! Google Earth says 5800km!
 
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#3
Back in the mid '90's I helped remove the 500KHz wire antenna off the ship. I wasn't a radioman, but I was friends with him. He was looking for some assistance and I was happy to get out of whatever else it was I should have been doing.
Anyway, I felt sort of bad taking it down. Like the end of an era.

So, anyway, back on topic...
Long wave worked well since it didn't skip. The ground wave nature of it worked well for beacon use since it was used for navigation. Same reasoning behind Loran, Omega, etc. You wanted a ground wave signal that wouldn't bounce off the atmosphere and screw up the pilot/navigator taking bearings.
Also, since there were hundreds, if not thousands, of these beacons in the world (at the time) being able to reuse frequencies was necessary. With the limited amount of spectrum available, it was useful that beacons usually only covered a few hundred miles.

Certain, under ideal conditions, it would travel farther, but that wasn't the norm.
 

ka3jjz

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#4
I don't know about that. The Longwave Club of America has been around a very long time, and they're dedicated to DX in the longwave band. The ground skip might be just one of the methods that LW uses to propagate, as it doesn't explain those folks that have European LW stations here on the East Coast (when there were a lot of them - not so much anymore,sadly). I understand that an over-water path is often favored, but it doesn't explain folks even hearing Trans Atlantics out in the Midwest.

I can't state this for sure, but I know I have read somewhere that LW also follows the Earth's magnetic field, and this is often the source of LW skip, much as the ionosphere accounts for much of the propagation at HF.

Interesting stuff. The LWCA (above) is a heckuva resource for this part of the band. Many members are hams, too...has a sterling reputation in the community, and has a wide variety of signals to hear (and sometimes decode)...Mike
 
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#5
The ground wave nature of it worked well for beacon use since it was used for navigation.
True - but what it does suffer from is coastal refraction, which is why most marine beacons are installed on headlands and points, often adjacent to a lighthouse. If the path of the radio wave crosses a coastline at anything other than a right-angle, then the received signal is 'bent' at the point of crossing - much like when you place a stick into shallow water. You have to very careful to plot the bearing and see if it crosses a coast back to the beacon and treat the result with some skepticism - especially if the navigator has been out on the bridge wing and taken a visual bearing on the co-located lighthouse when you proudly announce your erroneous radio bearing!

Another problem not in the marine environment but when aircraft use LF beacons is re-radiation. I was involved in the investigation and coroner's enquiry into an aircraft crash in a light twin where they descended into some wooded hilly terrain too soon at night in poor cloud conditions. They were looking for the overhead of the beacon to let them know they could descend and reverse course back to the airport where the beacon was located. However they were far too low and instead of the true beacon signal they had intercepted a re-radiated signal from a telephone line that had come from over the ridge in front of them that they could not see - there were two more ridges between them and the airport. As soon as they went over the ridge the 'signal' reversed bearing to the stronger signal behind them so they started to descend with fatal results.
 
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#6
From my personal 40 years of radio experience, I think (gut feeling) that up around 6 Mhz greyline prop is good for an hour or so before and after sunset, and this time decreases as the frequency drops. I've read some of the 160 meter hams talk about long distance prop peak for just a few minutes then disappear. MW BCB propagation is tougher to judge since stations are changing power levels and antennas at sunrise and sunset. My .02 cents
 
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#7
they all talk about HF greyline prop but nothing about LW. Most LW prop is via the ground wave which will go for 2000km under good conditions
You're right, the textbooks talk about the groundwave nature of LW freqs. This is amply demonstrated here at my QTH, surrounded by the Great Lakes, where many NDBs out to about 250 mi (particularily the Canadians) are heard 24/7/365 as their groundwave signals travel over the water. My experience with LW is relatively recent. However, it seems to me that there may also be a little talked about skywave nature to LW. Hence, my post about the seeming greyline propagation observed here recently.

Your 5800km DX shot back to England seems a bit far for groundwave. What do you think as you have had a lot more experience with this.
 
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#8
Long wave worked well since it didn't skip. The ground wave nature of it worked well for beacon use since it was used for navigation. Same reasoning behind Loran, Omega, etc. You wanted a ground wave signal that wouldn't bounce off the atmosphere and screw up the pilot/navigator taking bearings.
Also, since there were hundreds, if not thousands, of these beacons in the world (at the time) being able to reuse frequencies was necessary. With the limited amount of spectrum available, it was useful that beacons usually only covered a few hundred miles.

Certain, under ideal conditions, it would travel farther, but that wasn't the norm.
Pilots nowadays rely more on GPS than NDBs. If a NDB is used, it is not generally used for long range navigation but rather as perhaps a LOM. So, you are right about their range being intentionally limited in most cases.

My experience with Loran is limited to LORAN A which freqs IIRC were near the 160 meter ham band... not quite HF but certainly not LW. LORAN C was the LW version. Anyway, the navigators seemed to prefer pressure pattern navigation on transatlantic hops. When they figured we were nearing our destination (about 200mi out) they would turn on the TACAN tuned to the destination channel and sure enough the needle would soon start to come alive... uncanny.
 
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#9
Your 5800km DX shot back to England seems a bit far for groundwave. What do you think as you have had a lot more experience with this.
It had to be skywave as it was just dawn in the Gulf but the route was all in darkness. However the very upper stratosphere could have been catching the very early rays of the sun so who knows what was going on. All I can say is - it worked! Part of the mystery of radio. :)
 
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#13
I can't quite get my head around dBuV/m. It's another one of those meaningless numbers like the "Isotropic Radiator" it doesn't actually exist. Some of those field strength numbers are exceptionally small but I suppose you are expected to erect a Marconi Curtain in your back yard to get a bit of gain. :)
 
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