Downloading Satellite Images via FM Radio

Did you know weather satellites transmit their weather images over an FM frequency? And now that you know… You can intercept them yourself with a $10 FM radio dongle!

American NOAA weather satellites are in a polar orbit around earth, and each one will pass the same point approximately every 12 hours. When it is overhead, the signal is strong enough to receive. After [Matt] found out this tidbit of knowledge, he had to learn how to intercept the images himself.

The satellites transmit the images over the 137MHz band, and using a radio tuner USB dongle, you can record the transmission and then decode it into a picture. He used CubicSDR to tune and record the signal, and then Soundflower to pull out interference, and finally WXtoIMG — which starts recording when the satellite is above, and decodes the image.

[Thanks for the tip Amirgon!]

63 thoughts on “Downloading Satellite Images via FM Radio

    1. Build a turnstile, they are simple, then add a longer grounded turnstile below it as a reflector. you make basically a 2 element turnstile yagi that will significantly increase the signal to noise ratio and works great.

      They tend to work better than any of the fancy helix antennas and are dramatically easier to make.

      1. In the late eighties, Elector published a little circuit that together with a hacked FM radio could print the images directly on a facsimile. Depending on which satellite you tuned into, you could also print isobar weather maps.

          1. Hence the fact I shared the exact ones I have bought many of… I think I have had a dozen or so now and have given away several of them to just get people into the hobby. Feel free to pay as much as you like though. Those people charging 10X what they are worth will appreciate it. Cheers

          1. Very true. That’s what I started with too :) With the advent of all the digital/trunking a person might be able to grab a Bearcat or one of the RatShack Uniden Nascar versions for next to nothing now. Cheers

  1. Don’t those NOAA satellites encode the signal in pretty much the same format as fax machines? I seem to remember projects from the 1980s and 1990s that would use an FM radio with air traffic bands to tune in, and a fax machine to print the pictures. None of that fancy modern “computer” stuff required :-)

    ===Jac

  2. Now we need a cheap dongle in USB3.0 so we can see the HRPT not just APT…. I have yet to see a dongle that can handle 4.5MHz signal bandwidth and get it to the computer. If you know, please tell me. (Dongles, mind you, not $500 purpose-built SDR’s)…

    1. Take two cheap sticks, remove the XtAL from one and and connect the XTAL from the other (short wire). Then you have two inphase. But you will never be able to start both at the exact same instance, so you will need to cross correlate the output from both in software to calculate the relative delay between the two and eliminate it using buffer offsets.

      Now you will have two IQ streams that are phase coherent. The hard part is that these need to merged in the frequency domain so that instead of two 2.4MHz in bandwidth (no packet drops) you have something like 4.5MHz (you need a bit of frequency overlap to line them up in software)

      The above is not easy, to be honest it is a right pain in the butt, but if you want to pay only $20 for hardware then you will need to put in $$$ for software development time.

      A easier option might be the soon to be released “Airspy Dongle” (AKA “Airspy Light”) when it is available for about $100, I think that it will support 6MSPS.

      1. How about running a little SiLabs Si570 part (or GPS/OCXO disciplined Si571) at 4X the clock frequency, then divide down to the clock frequency in quadrature with a couple of really fast flip flops (from Perigrine or Micrel?) Then stick the I&Q clocks respectively into two RTL-SDR dongles then plug the two dongles into two USB ports? Maybe an Si5351 would work as a cheaper alternative to the Si570/571 (Adafruit sells a breakout board) albeit with higher phase noise – and it may even have a way to get quadrature outputs.

  3. I did this many years ago with a 486 and a scanner radio plugged into the soundcard a simple dipole antenna made from separating a speaker wire was more than enough to get a strong signal. It’s better if you can track the satellite online or with some software so you can know when it’s going to pass over your location. You’ll only have about a 2 or 3 minute window to catch the signal before you have to wait 12 hours to try it again.

    1. I ran across an old Windows 95/98 laptop that had a similar setup. It had that equipment all mounted in a briefcase, with a portable printer.

      It was one of a kind, but so was the 4-digit price tag. But somebody on eBay ended up happy with their new all-in-one NOAA weather laptop.

    2. I did this too. When I was a student meteorologist living out in the boonies without any decent dial-up Internet, APT and WEFAX came in really handy for sat pics, wx charts, etc.

      With a decent MW radio, you can still pic up many WEFAX stations around the world. Really handy when you’re on a boat in the middle of the ocean.

    3. I’m with you guys, I did this back in the mid 90s using firstly a radio scanner plugged into a sound card then a RIGST RX2 kit I bought from the (now mostly defunct I suppose) remote imaging group (rig.org.uk). I still have my RX2 kit and several other half completed units – I have the circuit diagrams with them. I made a custom case for mine from a radio shack (Tandy for me…) aluminium project box. I remember that we had big issues with signal bleed from stronger pager signals at the time…

      I really miss this aspect of my life, the closest I come to these days is the CB in my 4×4 or possibly my efforts with wifi antenna mods to my netbook.

  4. Nice, this packed in a go box was my idea, im glad to see someone did it. Quite useful even at this resolution , if you say…. lived in florida after a zombie apoc. Hurricanes would be pretty easy to spot.

    1. Zombies and bad weather. This is something you never really see comined. Probably because zombies eat people and bad weather wipes out zombies, so bad weather ruins a good zombie outbreak story.

  5. > Did you know weather satellites transmit their weather images over an FM frequency?

    Wrong terminology. It isn’t an FM frequency. FM is the modulation used at that specific frequency.

  6. Does anybody know, are these things still broadcast on HF too?

    As a kid I really wanted to build the RadFax decoder found here: http://www.americanradiohistory.com/Archive-Poptronics/90s/90/PE-1990-11.pdf. For reasons mostly involving lack of money I never did even though I probably re-read that article 100 times.

    Today, I know there is no point. I could do all the same plus more by just wiring the output of a receiver to my computer’s soundcard input and running some free software. Or, better yet.. use an RTL-SDR with a downconverter. But.. it would be very gratifying to achieve an old, abandoned goal. Even if I only ever use it once then put it away.

    I thought it was too late. The necessary software was not included in the magazine and what are the odds of the author being reachable at the same address 25 years later? Then I found this: http://www.siliconchip.com.au/Shop/6/2569

    I don’t know if/when I will ever bother but I’ve grabbed those files to save just in case! So, does anyone know if the HF signals this thing was originally meant to decode still exist? Or are the current satellite FM broadcasts compatible? If no and no then I guess I can still try using it for CW and RTTY. I wonder if this thing would work any better than the modern, software based decoders I have tried for morse code. None that I have tried worked very well at all.

  7. long ago I used to search and find obscure links/ftp’s from weather outfits where you could download the pictures fresh, but they kept closing them down after a few months so I got lazy and gave up. They were pretty damn good and large though.
    And they also used to have them on shortwave. I wonder if it’s all straight satellite now or if shortwave still has satellite pictures too.

        1. I can’t think of any off hand other than my own (and it is offline at the moment). But the setup can be as simple as an old win95 laptop, SeaTTY, a soundcard, a decent receiver like a Sangean AT-803 (really old and hard to come by, but was what I started with) or Degen/Kaito 1103 (what I have now, and plentiful on eBay) , and a dipole antenna.

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