Radio Amateur Copies Signal from Mars-Orbiting Satellite
arrl.org
arrl.org
If this is what he does for fun, I wonder what he does for work?
Notice that I'm not saying this to demerit any achievement. My intention here is to be encouraging in case you intend to give it a try. A similar setup could allow you to operate moon bounce (CW and FT8 seems to be pretty active) and also work the Es'hail-2 geostationary satellite in case you're in range. So it's definitely a very promising field to invest in.
Most of active hams are more interested on making short contacts and exchanging call signs. Scientific and technical experimentation is pretty niche. However, since the Es'hail-2 has launched (a Qatar geostationary satellite carrying an amateur radio payload on the GHz bands), a new opportunity of making a lot of short contacts using narrow band modes like Morse code and computer-aided modes has opened, and then I believe there are currently many people operating GHz-capable gear in the area covered by that satellite (Europe, Africa, parts of Asia and Brazilian northeast).
Although many of them are probably using their gear to log new contacts, you could say that they own the necessary setup to seek for satellite signals on that same band.
apropos I hope
He does electrical work for boats.
https://www.rac.ca/amateurs-in-the-news-scott-tilley-ve7til-...
Flagged the post as a result.
that seems surprisingly small. overall, impressive feat. would be interesting to know more about the gear. from the posted video, I guess he is using ettus b200, but thats just a guess.
https://www.nasa.gov/feature/jpl/nasa-s-deep-space-network-w...
I guess they achieve higher reliability than amateurs on a number of counts, but that contrast also makes the amateur efforts seem even more impressive. (Since area is proportional to the square of diameter, the DSN dishes would each be over 3,000 times larger than Scott Tilley's dish.)
DSN have way bigger requirements in terms of signal to noise ratios, since they need to demodulate received signals.
Scott Tilley, on the other hand, seems to be mainly interested on detecting the presence of signals, not necessarily extracting information from it. Then, he could build a bigger dish, but he doesn't actually need one to achieve his goal.
I notice that another guy commented here about that. His comment is dead now, but he had a point. I found it informative indeed, I've always asked myself why spacecrafts "wasted" energy with carriers and never realized they make the signal easer to find.
Not exactly. You need a carrier wave / signal to modulate information onto. Can't modulate info onto nothing.
But not to digress, it's likely 120 degree BPSK (i.e. QPSK with a DC level for the Q). I'm not in the deep space field (but do RF/Microwave professionally), but the DSN (deep space network) on Earth sends out a carrier with 120 BPSK modulation with PN (pseudo noise) code. The spacecraft transverts and sends that back (a bent pipe). Velocity is determined via Doppler shift of the carrier. Range from the delay in the PN code. So knowing velocity and range (and bearing using antenna pointing or interferometry), you can track the spacecraft with great precision.
Even without a bent pipe, you need carrier recovery first, before you can demodulate, and the leakage helps with that. You can also do geolocation with carrier leakage (e.g. ARGOS satellites) and via isodops (contours of constant Doppler shift) like a reverse GPS uses isochrones (contours of constant time delay).
So in short, there are benefits of wasting carrier energy. The ham guy can detect it as he can do lots and lots of coherent averaging (i.e. long FFTs or very narrow resolution bandwidths) to find that carrier. Though to recover any modulation will take a much bigger (or lower noise temp) antenna.
In case you have any links to share about how DSN works, I'd appreciate.
And thank you also for mentioning coherent averaging. I'm more or less familiar with the concept but I've been trying to find out the name of the thing so that I could google on how to implement it (I've been collecting some information for assessing the feasibility of a project involving high-loss antennas).
Besides, I've never wondered how they tracked spacecrafts, especially those ones as far as new horizons and voyagers.
https://www.amazon.com/Uplink-Downlink-History-1957-1997-033...
I'm also curious what prevents say an amateur operator or even another country from sending commands or disrupting communication to remote systems on Mars. Is it the just the amount of work they'd have to do, proprietary/secret protocol, encryption?
The practical requirements of getting a strong enough signal to Mars would require a big dish to focus the energy and some high power microwave equipment which make it more difficult but not impossible given enough resources. Then as you mentioned one needs to know the communication protocols.
BTW there were Ham built satellites in orbit, that piggybacked onto other missions. (OSCAR) Not sure if they are still in orbit. And again they used reserved spectrum for licensed experimental Amateur radio stations.
For example hams can only transmit in the 1.25 meter band if they don't interfere with other users like the Automated Maritime Telecommunications Systems (AMTS).
The occasional amateur gear is usually not enough to demodulate signals from Mars, since they're too faint. You'd need much larger dishes to, roughly speaking, "ingest" more energy into your receiver so that it become more distinguishable from noise and you can extract information from it.
It would be possible to demodulate with smaller, amateur dishes if the spacecraft transmitted in a very narrow bandwidth. It wouldn't make sense for space agencies to do that, though, since they would trade higher bit rates for cheaper receivers, whilst powerful receivers aren't that difficult to build and are totally on budget for an agency capable of launching a spacecraft.
But I must say that that would be a very nice citizen science project.