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Author Topic: Grey Line Propagation  (Read 447 times)
KC2BYV
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Posts: 51




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« on: February 05, 2008, 03:10:30 PM »

I've never fully understood grey line in my 4 months of HF DXing, but I think I was just given a lesson.

I just worked RTTY with the Southwest corner of Australia from New York, 579 both ways.  This is way farther than I have ever gone.  Wondering how, with a mere 90 watts to a G5RV on 30m, I pulled up a grey line map to see that we were both just about on it.  

Am I to understand, then, that the skywaves travel along the u-shape of the line, from my north to south to east and then a bit north again to reach VK land?  This seems to be a longer path than straight line.  Again, I'm just getting this, am I correct?


Furthermore, is this an indication of improving solar conditions, or is it common?  I usually never get to operate this time in the evening, and dawn is usually out of the question as well.
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WA3SKN
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Posts: 5457




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« Reply #1 on: February 05, 2008, 03:43:03 PM »

30 Meters is "the perfect" grey-line band.
Break out a globe and string, then plot your location and their location both direct and long path... you will probably recognize the path!
73s.

-Mike.
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WA3SKN
Member

Posts: 5457




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« Reply #2 on: February 05, 2008, 04:14:04 PM »

Local "time-of-day" is important in choosing the band of operation... as you have discovered.  Your best way of propagation "education" is to operate and have fun!
Enjoy!
73s.

-Mike.
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N2AXZ
Member

Posts: 90




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« Reply #3 on: February 05, 2008, 09:37:34 PM »

The "gray line" is a straight line over the earth's surface, as is any other great circle path.  The gray line is just the area surrounding the day-night terminator on the earth, which is always a great circle.  The reason that gray line propagation works so well is that the ionospheric conditions are essentially constant all along the path.  The lower layers of the ionosphere recombine most quickly, so signal loss due to absorption decreases rapidly with loss of sunlight.  The upper layers of the ionosphere are still relatively undisturbed, allowing long distance propagation to occur.  But gray line propagation is propagation in a straight line --- it only looks curved when viewed on a flat map.

David, N2AXZ
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K0SPN
Member

Posts: 12




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« Reply #4 on: February 06, 2008, 02:00:44 AM »

Hopefully you've caught on with the replies already given, but in case you didn't...

The "u-shape of the line" is most definitely NOT a "u-shape".
It looks like a "U" because you were looking at a two dimensional map and not making the connection that the Earth is round, not flat like the map you were looking at.

If you have a globe, sweet, otherwise, take any round object (basketball, orange, etc.) and shine a flashlight on it. Hold the light and the object fairly far apart.
Notice the light side and the dark side.
The "Grey Line" is the transition area from 'day' to night'.
The west (left) side, as you look at it, is at sunrise, the east (right) side is at sunset.

So, the grey/gray line is a straight line around the Earth that enhances propagation in certain bands.
I'm no expert on how, why, or what frequencies gray line enhances, but I know that it works.
It happens at sunrise/sunset and anywhere that is in the same or opposite condition will have enhanced propagation to your location.
Typical enhancement happens from anywhere between +/- 30 minutes of sunrise/sunset, so you may have a short window or you may have a longer one, it varies.
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N2JSO
Member

Posts: 21




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« Reply #5 on: February 06, 2008, 08:55:27 AM »

>I just worked RTTY with the Southwest corner of >Australia from New York, 579 both ways. This is way >farther than I have ever gone. Wondering how, with a >mere 90 watts to a G5RV on 30m, I pulled up a grey >line map to see that we were both just about on it.


Congrats!  That's as far away as you can get from NY and still be on land.  The antipode is a few hundred miles SW in the Indian Ocean.  You'd have to work a Maritime Mobile station (or EME) to go further.  Check out the Antipode Map at http://www.antipodemap.com/

I'm in New Jersey with a similar antenna setup.  Since becoming active again 2 years ago, I've heard (but could not work) Australia exactly once, just a couple of weeks ago.  It was also with greyline at both ends, and on 30m.

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KS2G
Member

Posts: 391




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« Reply #6 on: February 06, 2008, 07:42:32 PM »

For an excellent, easy-to-understand explanation of what's happening when you're "Working The Gray Line" go here:

http://www.qsl.net/w2vtm/grayline.html

73,
Mel - KS2G


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AK2B
Member

Posts: 94




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« Reply #7 on: February 07, 2008, 10:55:44 AM »

KS2G
That is a good reference and easy to understand. I’ve learned a lot from Paul Harden, NA5N. You can find some very good explanations of general propagation by doing a search at http://www.kkn.net/archives/html/QRP-L/ and putting “NA5N” in the search field. He has a gift for explaining this otherwise complicated subject in human terms.

KC2BYV
http://www.dxatlas.com/DxAtlas/  Here you can download a trial of DX Atlas where you can view the gray line in real time on a three dimensional globe.. The program will also do real time MUF charts when used with IonoProbe (available from the same author).

Tom, AK2B
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