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International Space Station Downlink!

I downlinked a data transmission directly from the International Space Station! This amateur radio stuff is getting exciting. Using an orbital tracker tool, I found the time and location when the ISS would pass overhead here. From 9:16 AM to 9:21 AM, rising to the south, reaching its zenith to the southeast with 19 degrees elevation above the horizon, and setting to the east. I went to the top of a hill in my neighborhood, tuned my simple handheld radio to 145.800 MHz, pointed the antenna, and waited. And suddenly I heard crazy beeping! Dog walkers were staring.

Supposedly you should hold the antenna horizontally for best results, and perpendicular to the line to the ISS. But I just sort of waved the antenna around frantically, searching for the orientation that brought in the cleanest signal. I used the voice recorder app on my phone, holding the phone up to the radio speaker to record the beeping audio, while the wind made noise and cars drove by and the signal faded in and out. I captured almost all of one two-minute transmission and part of another, before the ISS went out of view. It was several minutes of recorded whistling and beeping.

Back home, I used some software called MMSSTV to decode the recorded audio, which was a PD120 slow-scan television image transmitted from the ISS, part of a special event celebrating women in space. The software provides options for tweaking the signal sync, phase, and image slant, because the Doppler shift screws up the signal when the ISS is moving by at 17500 miles per hour. Here’s the final decoded result. Peggy Whitson PhD, first woman ISS commander. Transmission received directly from Earth orbit, Sputnik style. Good morning!

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