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Radio Amateur Copies Signal from Mars-Orbiting Satellite (arrl.org)
173 points by wglb 18 days ago | hide | past | favorite | 37 comments

This is nothing short of incredible. Radio is hard, even at HF (1-30mhz). It's very forgiving at HF though, and so is very approachable. This is where I spend my ham radio time dabbling and hacking away at things. VHF is harder, and UHF an order of magnitude harder. But 8-12Ghz? That's not for mere mortals. It's machining pieces at tight tolerances and movement measured in the smallest fractions.

If this is what he does for fun, I wonder what he does for work?

I have no hands-on experience with homemade equipment for the GHz bands, but I've read that they are a bit less challenging than it seems at a first glance. Mostly because of the availability of GPS receivers providing highly stable, relatively cheap frequency references for transverters.

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.

As an outsider what’s the order of magnitude on humans that have this setup currently functional? 100? 1,000? Etc.

There are 774,562 amateur radio licensed people in the US [1]. I would assume 10% of them are super active, so 77,456, and of those super active people, I'd say 1% of them are pushing the boundaries. So 1000?

[1] http://www.arrl.org/fcc-license-counts

This comment is amazing. Thank you so much.

That's a good question. I don't know how to estimate, but it might be around the thousands in fact.

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.

>If this is what he does for fun, I wonder what he does for work?

He does electrical work for boats.


You have to make a blood sacrifice to the Voodoo gods in high speed electronics if you want it to work (is the saying, anyway) - i.e. the actual shape of the traces on the PCB starts to become important, and one can use this fact to form things like filters and directional couplers.

> He uses a homemade 60-centimeter dish and relies on software-defined radios (SDRs) to accomplish the task.

apropos I hope

Cool. This Canadian amateur, Scott Tilley VE7TIL, is the same operator behind previous discoveries like a NASA satellite thought to be dead three years ago.


I wonder if ARRL knows there’s malicious ads on their site. Reader mode saves the day!

I'm pretty sure it's curse of HAM-Websites ! They either have malware or looks like frontpage2000 projects. Not dishing just noting ! Big fan of hams !

I can confirm that I got some sketchy stuff from this site. It showed me an I’m not a robot butting which I stupidly clicked. Went and cycled my passwords to be safe.

Flagged the post as a result.

Wow, I'm a ham radio operator and today during Perseverance landing I was wondering if it would be possible to receive signals from orbiters on Mars using homemade equipment. Now I have my answer.

And his dish is only 60 cm dia.

Those 60 cm are probably enough for his requirements. It seems that he's mainly interested on detecting signal presence, but not necessarily demodulating it. Then, I suppose that the signal-to-noise ratio provided by his small dish is sufficient

> He uses a homemade 60-centimeter dish

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.

Apparently the Deep Space Network dishes are (now up to) 34 meters:


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.)

Indeed, but there are other important factors besides size.

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.

Thanks for that clarification (to you and the author of the dead sibling comment)!

And smaller dish has larger beam width, making it really difficult to track the signal.

I'm the shadow banned commenter, due to comments that fall in the right half of the plane; disagreeable to HN mods.

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.

Thank you so much for the information.

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.

Uplink Downlink is a good, technical history:


> 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.

Yes, you can. There are a number of supressed-carrier modes, e.g. single side band.

He is detecting, not demodulating, which is what the big dishes are for. Most deep space comms have carrier leakage (on purpose) for ranging. That’s likely what he is detecting.

60 cm of near infinite resolution is still a crazy amount of data

If anyone's interested in getting started with space signals, check out AMSAT. https://www.amsat.org/

Is the arrl website hacked? Whenever I click on text, I get ad pop ups.

I think it got in due to the ads.. I've reloaded the page and it doesn't hijack the links anymore.

Yes this website has been hacked...

As someone not familiar with ham - what can you do with this signal? Can you decode it to view stats or pictures? Or is it mostly just "hearing" it speak to Earth?

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 amateur radio frequencies that are "legal" for a ham operator to transmit on are well defined. If the NASA devices used Amateur frequencies for commercial work I believe they would be breaking US law as well. So the terms of the amateur license prohibit transmitting signals to the remote systems on Mars.

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.

What you said is mostly true but there are also frequencies that ham operators can transmit in, but only have secondary priority to other uses.

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).


My two cents in addition to lebuffon's reply:

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.

Warning: I think that sometimes this page loads malicious ads that hijack the links on the pages.

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