Writing a RF weather fax program

Writing a RF weather fax program

This is received on 8038 kHz, with a cheap Tecsun 1 kHz step SSB receiver, indoors with a small telescope antenna: wget

formatting link
Converted to mp3, recorded as 48 kHz 16 bits wave on a solid state recorder from that Tecsun SSB radio, note the noise, fading. like the waves of the sea, coming and going...

So this is basically 2 kHz frequency modulated... (has greyscale) This is what the 'hamfax' program makes of it (without further adjustment to be honest, it expects 1.9 kHz f0):

formatting link

This is what my program makes of it (converted to jpeg from bit map sort of thing):

formatting link

I left it running (not waiting for the sync field), so from top to bottom you see: the end of the previous weather map noise (as no signal) start tone (300 Hz modulation) sync pattern and image data end tones

The noise is now 'noise', you can see it breaking up in places, halfway through I switched the Tecsun receiver to wide band, it seems to help against the noise. Note that a lot if the interference bands are now not present as in hamfax...

I use a different FM demodulator in software, just the old zero crossing detector, gives me 20 data points per period, average over some 20 points, 500 ms per line, converts nicely to a 1200 pixels width from 48000 Hz (integer division). You can clearly see the UK, Spain, Netherlands, outlines.

Am adding auto save, so it will just keep running and save received charts. Has some more auto adjustments... Settings saved, keys to adjust picture. Who needs Fourier...

-rwxr-xr-x 1 root root 30552 May 18 16:56 pwfax*

30 kB

BTW I use the same system to detect the 300 Hz start tone... And that seems to work too. Its faster than hamfax (a lot), ist smaller, it uses no other libraries than xlib itself...

Reply to
Jan Panteltje
Loading thread data ...

I've done that myself however, I never included the Start and End syncs because at the time of the writing I couldn't find the specs and it didn't seem that important at the time, I can shift the image on the fly to center is once started.

What I do like using it for is to align the program for all the other modes.

Jamie

Reply to
Maynard A. Philbrook Jr.

On a sunny day (Sun, 18 May 2014 19:12:47 -0400) it happened "Maynard A. Philbrook Jr." wrote in :

This guy wrote one too, it works, but not on my eeepc (old java), and not on my laptop otehr java): file:///root/download/html/JWX.html He sailed around the world using it too, the 'specs' are on that link.

As far as my (first 701) eeepc goes, the company that wrote the OS no longer exists.. no upgrades. Now there is an other project, I have Puppy Linux on it too, will keep it around though, collectors item :-).

Yes, but to auto-save each chart I need to know where it starts and at least where it ends.....

Yea well, I at this point I only need the charts. My SSB radio:

formatting link

But again, bloatware seems to rule: # l /usr/local/bin/hamfax

-rwxr-xr-x 1 root root 3350098 Apr 26 10:47 /usr/local/bin/hamfax

-rwxr-xr-x 1 root root 30552 May 18 16:56 pwfax* Factor 100! And I already have more options.

I wrote the C code because the original idea was to use a PIC 18F14K22 internal hardware comparator to detect zero crossings (sort of use as FM limiter), but I thought 'better test the concept quickly in C' (PIC asm coding takes a while). I need a 1200x1200 screen _at least_ anyways (and do not have a 2400x2400 monitor yet), so why bother with PIC, use the soundcard.

I am contemplating making a 4046 frequency generator FM modulated by the soundcard later for test signals for more advanced features (4046 running at 2 kHz FM modulated by 300 Hz sine to simulate weather fax start tones, etc). Have a 4046 testboard somewhere if I did not use it for something else.

Reply to
Jan Panteltje

Correction:

Sorry, copied it to local, this is the real link:

formatting link

Reply to
Jan Panteltje

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.