It’s kind of interesting how entries for this blog will sometimes just jump out at you out of nowhere. Weather faxes are a great example of this.
Weather fax, also known as wefax, is one of those interesting technologies that’s been around forever on the shortwave bands. Back before satellites and the internet, this could’ve been the only way for a ship at sea to get any kind of weather forecast maps. It’s also something that’s never worked for me.
I have been trying to decode weather faxes on and off now since 1993. It’s not like I’ve tried for 20 years straight either, but every time I have given it a whirl I’ve failed. Chalk it up to crappy software, a poor interface, misconfigured computers, or just plain old operator error (my bet is on the latter), but I’ve never been able to pull it off.
Now, armed with a Perseus SDR and a program called SeaTTY, I decided to give it another whirl. Much to my amazement, I ended up with the following on my screen:
Holy crap, it’s working!
I think the key to getting it to work this time is a combination of the SeaTTY software and the Perseus SDR. The SeaTTY software is nice in that it has a built in automatic frequency control (AFC), which makes tuning the signal a relatively simple procedure. Just get the station in the pass band, switch the program over to WEFAX mode, and off you go. The Perseus also takes some of the guess work out of the process by letting you see the signal as well as hear it. Being an SDR, it’s also a lot easier to get the signal from the radio into the computer. With the Perseus, it’s just a matter of configuring the virtual audio cable software once and you’re good to go for just about every digital mode, whether it be PSK31, slow scan TV (SSTV), or weather faxes.
Obviously the image quality isn’t all that great. All in all, it looks just like what it is: a fax. You’ll also see that there’s some work that needs to be done on some of these images after you’ve grabbed them. Sometimes the ‘skew’ can be off, and the image will need to be adjusted. You can see a litle of that in the image above, but this one wasn’t too bad. Others have required some TLC in Photoshop, but it didn’t take too long to put them back in to a coherent image. here’s a couple that went through some time in Photoshop:
All of these weather faxes originate from here in the US, but there are other applications out there. Supposedly there is a Japanese station that’s broadcasting newspapers in both English and Japan. I haven’t found that one yet, but I’ll keep you posted. Until then, here’s a list of weather fax stations around the world, courtesy of NOAA, in pdf form.