Another try at an HF FAX decoder…

February 13, 2010 | Amateur Radio | By: Mark VandeWettering

About two years ago, I spent an evening and hacked together a simple program for taking recordings of HF-FAX transmissions and converting them into image files. The other day, I thought I’d dust that code off, but I couldn’t find it. So, instead, I reimplemented it from scratch. There is an interesting bit of math that I finally understood when I reimplemented it, which actually worked out rather well. I took a recording that I made of the New Orleans Coast Guard’s station broadcast, and it turned into this picture:

hffax

I’ll have to work a bit on the sync detection and scaling, as well as rectification, but it’s looking pretty good for the small amount of effort I’ve placed in it.

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Comments

Comment from Eldon Brown
Time 2/15/2010 at 6:32 pm

Mark.

I enjoy reading you adventures with WX FAX displays.

Several years ago (maybe 20 or so) I was playing with some code that I wrote to display HF-FAX, I wanted to to see what I could do with the data – I tried displacing (and smear) the pixels “up” within the display image, dependant on it cloud brightness and then merge it back with a base map – the results was very interesting fake 3D like display. My code processed the image from top-to-bottom and therefore it was done in place on a small machine, It was most interesting for viewing circular storm patterns. For a long time I kept several of the most interesting images, but alas, now they are lost.

As fast as you write code, I am sure you could do something similar in few minutes.

Eldon – WA0UWH

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