Let’s Get Started!
How I Captured a Satellite Signal from Space for Under $20
In the last post, we explored how certain weather satellites constantly transmit unencrypted analog images of Earth using FM radio signals. These transmissions, called APT (Automatic Picture Transmission), are surprisingly accessible. With just a bit of basic equipment, you can receive and decode them yourself.
Now, let’s actually do it.
Before we get started, I need to give an honorable mention to Gabe Emerson and his YouTube channel, saveitforparts. His videos, especially this one, got me started on this path and I highly recommend watching if you’re interested in this stuff. One thing to note, he recommends starting with NOAA-18, but unfortunately that satellite has failed and was officially decommissioned on June 6, 2025.
What You’ll Need
You don’t need anything fancy, just:
- A handheld radio that can tune to around 137 MHz in FM mode. I used the Baofeng UV-5R, which costs less than $20.
- A smartphone with an audio recorder app.
- Android: WAV Studio
- iPhone: Still searching for a reliable WAV recorder option—suggestions welcome.
- Optional: a longer antenna like the NA-771 to improve reception.
Step 1: Find a Satellite Pass
You’ll want to catch a pass from one of the NOAA satellites still broadcasting analog APT signals.
There are also two Russian satellites, but they broadcast a digital signal which needs a more specialized process to receive and decode. It’s still fairly simple and inexpensive to do, and I’ll cover that in a future post.
To find out when a NOAA satellite will pass over your location, use one of these tools:
- n2yo.com
- ISS Detector (mobile app)
- Heavens Above (mobile app)
Using n2yo.com:
- Go to n2yo.com.
- Click Most Tracked, and then on either NOAA-15 or NOAA-19.
- Click on the “10-day predictions” link.
- Click the “All Passes” tab near the top.
- Look for upcoming passes with a high maximum elevation. The higher the better! Close to 90° is ideal, meaning the satellite will pass nearly directly overhead.
- Write down the start and end time, and look at the top right corner of the screen to get the frequency. It will be one of these two:
- NOAA-15 (137.620 MHz)
- NOAA-19 (137.100 MHz)
Step 2: Set Up and Record
- Set your radio to the correct frequency and FM mode (not narrowband FM).
- Use the best antenna you have and hold the radio vertically up and down.
- Turn the squelch of your radio all the way down until you hear static. If using a Baofeng, you’ll need to go into the settings and set the squelch to “0”.
- Start recording audio on your smartphone either at the start time of the pass, or once you hear the signal. It’s up to you.
- As the satellite passes, rotate your body to keep the antenna roughly aligned with its arc across the sky. No precision tracking needed, just follow it “by ear”. You should hear the signal getting stronger or weaker as you rotate, but keep in mind it will also fade out as it starts to set below the horizon.
If you want to hear what this sounds like, I included a sample recording in the previous post but here it is again:
Step 3: Export and Decode the Audio File
After recording, you’ll need to export your audio in a specific format:
- WAV format (*.wav)
- 16-bit PCM
- 11025 sample rate (very important!)
To decode the signal:
- Go to open-weather.community/decode
- Upload your WAV file
- The default settings should be fine, but:
- Selecting “Equalise” can improve the image in noisy recordings.
- If your satellite passed south-to-north instead of north-to-south, use “Rotate 180°” to flip the image upright.
- Click “Process”.
If all goes well, you’ll get your first weather image, received directly from space, using gear you can buy for less than a pizza!
Don’t Worry If It’s Not Perfect
Noisy? Incomplete? Off-center? That’s all normal. If you managed to record anything from space, that’s a win. You can always try again, and you’ll get better with practice. If you want proof, check out my early results here:
https://www.littlegreenlights.com/i-downloaded-a-picture-from-space
What’s Next?
In upcoming posts, I’ll cover:
- Using software-defined radios (SDRs).
- Getting better reception with different antennas.
- Receiving and decoding higher-resolution images from Meteor satellites.
But for now, you’ve done the hardest part: you got started. Be proud of yourself! Go crack open a tasty beverage!