Thursday, December 5, 2013

NOAA Satellite Recording Decoder Problem SOLVED! Well, solved for now........

Well, well, well.......

I "solved" my problem in kinda-sorta in a back-handed way, but at least now I know what I was doing wrong.

Earlier today I replied to Silicon Graybeard that I was going to try an old program I used to use to decode the audio recordings I made from the NOAA APT satellites. I tried installing WXsat on my Windows 7 PC that I use for my Amateur Radio activities, and it simply wouldn't run, regardless of whatever "compatibility mode" settings I tried. I then installed it on my Linux machine using Wine, and it ran!

The first snag I hit was that since this old program was meant for Windows 95, it couldn't handle long file names, and errored out when trying to load the recorded wave files I had. I renamed the files, and then the program informed me it could only handle MONO files. Using Audacity, I converted the recording to single track mono, and tried again.

It then threw another error, saying the files had to encoded at an 11025 Hz rate, which I remembered from looong ago, so back to Audacity to resample them from the 48kHz rate down to 11.025kHz.

Lo and behold, it accepted the file, and processed it, producing this image:

The right-to-left shift in image was caused by me doing something (I don't remember what) during the recording.

The "stripes" on the edges of the image are synchronization and telemetry frames, explained in this drawing:

Here's an image of both channels, which is easier to relate the above drawing to:

Switching to NOAA_IR (Infrared Mode), produced this image, where you can see the California coast down the approximate center:

SO....not having anything else to lose, I fed the  "remastered" file into WXtoImg, and it worked:

I still don't have the hang of flipping the images to "get them right", so until I get a longer recording, that shows more of the coast, I'm not sure what to do to "normalize" them so they look like I'd expect them to, like you're looking at a map in an atlas.

Now the interesting thing about this, is NOWHERE in the docs for WXtoImg can I find a warning, or caution, about how you have to feed the program an 11.025kHz, mono audio file, and in fact, all the things I found about "piping" the audio to the decoding program from the SDR receiving program via a Virtual Audio Cable say to leave things set at 48kHz.

It *might* accept a stereo file in some rate other than 48kHz, or it *might* accept a mono file at 48kHz, or it *might* require an 11,025 Hz, mono file, just like my "old" program.

Or, I *might* be able to get the SDR programs to save the audio from the dongle in the correct format of whatever, and not have to mess around converting the files after I've recorded them, I just don't know at this point.

And it's 2145 local time, and I have to be in to work tomorrow at 0600 for more training (we had Fiber Optic stuff today) and certification classes tomorrow, so good night, and hopefully I'll get a nice long pass recorded tomorrow so I can mess around with the decoding options now that I know I have something usable.


  1. Well, this IS keeping you out of the bars... LOL Glad you've been able to 'fight through' the issues to get it to work!

  2. yuk-yuk!

    That's why they (used to!) pay me the Big Bucks at work!

    Well, Boeing did.......

  3. well, I am walking in your shoes too..
    nice, I found your post!


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