Sat On A Light

There have been amateur radio satellites in orbit for literally my entire life. Hams were in space only four years behind the Russians, less than a year before I was born. It also was the first satellite deployed as a secondary payload from a primary launch… ejected using a spring purchased from Sears. Remember, it doesn’t *have* to be expensive to work, but if *my* life is in the balance, I’d rather it was. It should at least be a McMaster-Carr spring…

The first time I heard of amateur radio satellites, I presumed that was an exotic part of the hobby that only the ham elite (read: rich hams) would ever have access to. I think a big part of that was the math needed to predict orbits and the presumption that exceptional precision would be needed. Turns out that it’s not particularly difficult, but neither is it trivial. Johannes Kepler figured it out on paper by candlelight. With the advent of personal computers in general and the ubiquitous smart phone in particular, much of that number crunching is a few finger swipes away. Now working satellites seems to be reduced to learning the idiosyncrasies introduced by chasing a slowly tumbling 1/2 watt transceiver 300 miles away while it flies by at 17,000 miles per hour. Piece o’ cake.

I exaggerate the difficulty, though not the conditions. As rough as that sounds, it can be done with as little as a handheld antenna and a dual band HT, assisted by some tracking software.

Armed with some basic tips obtained from various YouTube sources (which I will detail below) and an Android app, I was able to pick up the beacon on a couple of satellite passes with only my existing base station gear, an Icom IC-7100 and a Diamond X-300A. This is a fixed base station antenna optimized for transmitting and receiving towards the horizon.

Undocumented Satellite Beacon Pass

Note that I am chasing the Doppler frequency shift, which is one of the two biggest idiosyncrasies. Satellites are moving fast enough for Doppler frequency shift to matter. Most satellites operate crossband, with an uplink that is either 2M or 70cm and a downlink that is the other band. Obviously both are affected by Doppler shift, but as it is a percentage effect, the higher the frequency, the larger the effect, so 70cm is more affected that 2M.

Having now heard such a birdie tone intentionally, I am reasonably sure that I have accidentally heard them before and perhaps just didn’t realize it was a satellite! How simple must it be if I can do it accidentally?

I have tried a couple times since then to hear QSOs and I can *just* tell there *might* be something there, maybe the tiniest bit of a beat tone tuning the range, but not enough to pull out of the noise.

To give myself the best chance of success, I ordered an Arrow 146/437-10WBP antenna. This is a 3 element 2M and a 7 element 70cm on a shared boom. The BP suffix is the split boom (back pack) version which breaks down easily for transport, so I also got the carrying bag for it. At this writing, it has not yet arrived. Being a handheld antenna, it helps with the other major idiosyncrasy, polarization fading. As the satellite tumbles in microgravity, the antennae are changing orientation and being able to rapidly change polarization is one strategy for coping with that. Antennas built with circular polarization is another.

My plan to start is to try FM using two handhelds. I have 2 each Baofeng UV-5Rs, RD-5Rs and an Icom ID-51, so I can mix and match as necessary.

I also used this as an excuse to picked up an SDRPlay receiver, the SDRdx model. I have nearly purchased an SDRPlay receiver a few times over the last few years, but never pulled the trigger. I’m not sure if it will actually be used for satellites or not, but I imagine I will at least experiment with it. Plus, everything else you can do with an SDR 🙂 Not necessarily only for satellite use, but for very wideband SDR reception, I got an MFJ-1866 discone antenna. This will be my first experience with a discone. This model can do double duty as a 200W transmit antenna for 2M to 23cm as well. It might become the first antenna mounted on the house, as opposed to the workshop.

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.