My friend Greg and I spent several nights this past week attempting to listen to amateur radio signals from the International Space Station (he’s been using Gpredict to find time windows of orbits close to us). Not only is one of the crew members on the station a ham, but they also have a fully functioning repeater on the station as well. The uplink frequency is 437.800 MHz and the downlink frequency is 145.800 MHz. I had my squelch turned to minimum and my volume set high, but I never heard anything but white noise. Oh sure, I fleetingly thought that I had a variety of contacts, but that was just my brain playing tricks on me. It’s a well-known psychological quirk that people can fool themselves into hearing meaningful noises in pure static, or seeing patterns in random shapes.
I spent twenty minutes on each of several different nights listening to white noise, straining with all my mental might to hear something amidst the cacophony. But we never heard anything. None of the orbits brought the ISS closer than 800 miles. It was simply too far for our receiving equipment. We both have 44-inch magnetic mount dual-band whip antennae, the kind that can be affixed to the top of a vehicle. They’re good for ground-based mobile operations, but not for trying to receive signals from space! For that, you really want a cross-polarized Yagi antenna on an altitude-azimuth mount (imagine how large ground-based telescopes are pointed and you’ve got it). And that represented a far larger investment in the hobby than either of us has made so far. Are receiving transmissions from space limited only to the upper echelons of the hobby? Is attempting it with entry-level equipment as foolish as someone with a cheap telescope from Wal-Mart searching for a new planet? I would soon find out.
After another annoyingly silent ISS pass last night, gpredict showed that the biological research satellite GeneSat-1 (see picture above) was passing almost directly overhead in another twenty minutes. It also happens to be equipped with a beacon operating in the 70cm amateur radio band. I was skeptical, and it was getting late, but I couldn’t miss the opportunity. This would be four times closer than any pass of the ISS so far (and thus sixteen times the signal strength, thank you inverse-square law), so I was hopeful. The frequency of GeneSat-1′s beacon is 437.067 MHz. I can only tune my radio in 5 KHz increments, but the Doppler shift of the orbit spreads the signal out enough that it would be heard on the frequency I tuned my radio to, 437.065 MHz, if indeed the signal was strong enough to be heard at all.
So again I turn the squelch all the way down and the volume up to almost painful levels (if you’re a fan of overblown metaphors, imagine a fighter pilot setting his afterburners to maximum, his plane roaring and rumbling around him). I listened intently as the minutes slowly ticked away. GeneSat-1 crested the horizon; nothing. It began rising higher and higher in the sky; still nothing, though my mind was now alerting on fake signals at an alarming rate, only for each to be rejected after a moment’s consideration.
GeneSat-1 reached its maximum elevation in the sky. I thought I heard something. It seemed different than the other fake signals thus far. I couldn’t make out anything other than a just-barely-there rhythmic pulse of not-quite-random noise with a period of around five seconds. And then I began hearing quieting of the white noise on a five second interval. I was definitely getting enough signal to at least suppress the noise, although the content of the signal itself wasn’t quite strong enough to register. My lingering doubts faded away and I knew that I was really hearing something, something from space.
Then in a triumphant outburst, I plainly heard an AFSK1200 transmission during one of the quieting periods (if you’re old enough to have used a dial-up modem, it sounds exactly like that; if not, imagine a really spastic, hyper, angry bumblebee). It repeated every five seconds, growing louder and louder, each transmission less than a second long yet containing the satellite’s identifier callsign along with some basic telemetry. I didn’t have my radio hooked up to my computer to decode the transmission, but I didn’t care. I was hearing a transmission from space, a radio signal emitted from a tiny 10 pound satellite whizzing over my head right at that very moment at thousands of miles per hour!
The transmissions disappeared just as quickly as they had appeared. All in all, I had heard maybe ten beacon transmissions. The satellite was now rapidly moving down from its peak in the sky (from my perspective). The pervading random static returned once more, but my mind was no longer making up signals amongst the white noise. Having heard a 6-inch long satellite in orbit 200 miles above me using nothing more than a car-mountable whip antenna, it had no reason to make anything up now. The experience had been unreal enough already. I listened to the no-longer-infuriating white noise for another couple of minutes, then went to bed.