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Author Topic: WeFax dark bands.  (Read 11647 times)
N6SBN
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« on: September 27, 2013, 09:01:04 AM »

 Using FLDIGI.   I get a fair picture, but there is some banding. (dark lines)  How do I adjust this out of the picture?.

Thanks in advance.

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AD9DX
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Posts: 1481




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« Reply #1 on: October 03, 2013, 07:35:55 PM »

Could it be a bandwidth issue?
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EX, KC9TRM, KB9IRZ
VA7CPC
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Posts: 2386




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« Reply #2 on: October 05, 2013, 09:25:10 PM »

Unlikely to be bandwidth.

The WeFAX encoding is white / black, using two different frequencies.  Each horizontal line is sent in (I think!) 0.5 seconds (120 lines per minute).

Are the black bands horizontal?  If so, something (either local or distant) may be turning on and off, interfering with signal reception.

.       Charles

PS -- I've never tried Fldigi for WeFax, but it's a really old protocol, and all software should work pretty much the same.
 
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WD8OQX
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Posts: 45




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« Reply #3 on: October 07, 2013, 08:14:56 PM »

On what freq. & at what time(s) are you copying this?
I have FLDIGI & can check to see if I get it too.
Then maybe can figure out what it may be.
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K3DCW
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Posts: 193




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« Reply #4 on: October 08, 2013, 09:26:59 AM »

Using FLDIGI.   I get a fair picture, but there is some banding. (dark lines)  How do I adjust this out of the picture?.

Thanks in advance.



It depends what you mean by "banding".  Due to the nature of HF, you will get some black lines from time to time, usually due to lightning crashes, unless you have a VERY strong and steady signal.  An image of what you're seeing may be useful.

Remember, most fax transmissions run at 120rpm, meaning they're painting 2 lines each second; one good noise crash or fade and you will have lines on the image...it is the nature of radio. 

73

Dave
K3DCW
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N3HFS
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Posts: 212




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« Reply #5 on: October 09, 2013, 07:10:15 AM »

Something as simple as someone tuning up nearby (a steady carrier for a second or two or longer) will cause dark, horizontal bands on HF fax images.
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