Forever enslaved to the enticing YouTube recommendation algorithm, one night I came across a particular video advertising the possibility of pulling images directly from weather satellites. Curious as to even the legality of such a feat, I watched the video and soon realized that I had to try for myself. There was one problem though; they used a $300 radio and had a team of students under the direction of a supervisor and I have the budget of a broke college student and no friends. Determined to produce similar results with less than half the budget and manpower, a few weeks later I found myself dragging my roommate to Home Depot.
What it does
Our setup allows us to receive the signals in which weather satellites transmit, and record the audio which we hear. The WAV audio file is then resampled, decoded, and then produces JPG images of the area!
How we built it
Our antenna is fashioned after a standard double-cross dipole antenna, with each dipole measuring ~19". This is near the ideal length to receive frequencies around 137MHz, which is where the US government's very own NOAA weather satellites transmit. This double cross design takes two pairs of dipoles with different length connections and effectively phases two signals onto each other. In theory, this should allow our antenna to operate omnidirectionally.
To build the antenna, I bought an software defined radio (SDR), which eliminates both the cost and bulk of a radio more typical to HAM radio operations. SDRs instead utilize software to control operating frequencies, gain, and many other functions rather than using built-in tuning mechanisms. Our radio comes from RTL, and software for this particular device was readily available to use. This radio has an impedance of 50 ohms, so I bought some cheap 50 ohm coaxial cable from Amazon to go with it.
The harness itself is built from 3/4" PVC pipe, and holds the very shadily soldered connections between each arm. The dipoles themselves are made from measuring tape where ~1" of coating was sanded off for better connections with the coaxial cable. The vast majority of the antenna is held together with a total of more than half a roll of electrical tape.
Challenges we ran into
Wow. I am really bad at soldering things. This caused issues when putting the coaxial connections into the PVC arms since they didn't particularly want to fit and my soldering wasn't in any shape to really do anything more than exist. As a result, most connections were taped and were very flimsy.
Additionally, being located in near a city and on a college campus also produces a ton of radio interference around the FM and air bands, which are very close to the signals we were trying to receive. In some of our experiments we could even hear voices with the FM interference from local radio stations. With our data being taken so sporadically, we had very little time to attempt correcting for this interference and other user settings. Each of the three satellites I utilized have orbital periods of ~103 minutes, and not all of their approaches were far enough above the horizon to make contact. For most of the hackathon we were able to record data once every 1-2 hours, however there was a large gap between 10:42PM and 5:15AM where there were no viable passes.
Accomplishments that we're proud of
The antenna managed to receive audio and with one of the images from NOAA 19 you can recognize the Great Lakes and St. Lawrence Bay!
What we learned
Through this experience, I have learned a lot about radio theory and its practical applications. While learning about the theory behind this antenna, I also became interested in HAM radio and began studying for the entry licensing exam. Roughly an hour before walking to the registration table at BrickHack V I tested for and passed this exam and now hold a Technician Class license.
On other the other hand, I have also learned a lot about the fabrication facilities on my campus (University of Rochester) and have interacted with more faculty and students outside my department for advice than I have for any other project.
What's next for Satellite Imagery
The next step in this project would be to create a sturdier and more permanent antenna. One of the biggest flaws with the antenna was how wobbly the harness was and how flimsy the connections between wires were. While I was still able to pull images from this set up, it is not suitable for operation in precipitation and a support even broke throughout the night.
With a studier antenna, I should be able to find a stronger signal more easily. Being able to receive stronger signals from NOAA satellites allows you to pull additional telemetry data and thermal images, in addition to receiving much higher resolution images. I should even be able to access the METEOR M2 satellite with a better antenna, which broadcasts a digital frequency and produces colored images.
Having a network of people pulling images from these satellites can allow for more creative results as well. For example, a composite image of Earth can be created with enough people and if consistent, can produce a sort of "citizen's Google Earth."