Tom Nardi
Dan Maloney 3:00 PM
OK folks, good afternoon and welcome to the Hack Chat! I'm Dan, I'll be modding today along with Dusan as we welcome David Prutchi to the chat. We're talking Deep Space DX, and I'm pretty excited about it myself. Welcome David!
|
David Prutchi 3:01 PM
Thank you Dan! Excited to be here!
|
|
Dan Maloney 3:02 PM
So how did you get into satellite listening? It's not really an everyday hobby, is it?
|
|
David Prutchi 3:02 PM
It's not golf for certain...
|
Boian Mitov 3:03 PM
Hello @David Prutchi :-)
|
|
David Prutchi 3:03 PM
I grew up in Ecuador, where NASA had a tracking station at the base of the Cotopaxi volcano. I would go there as often as I could get my dad to take me. I was present during the tracking of the Apollo-Soyuz missions and that got me hooked.
|
amiboy 3:04 PM
hello all
|
Ben Wasserman 3:05 PM
Hi David!
|
|
Dan Maloney 3:05 PM
That's so cool! I tend to think of the DSN now as pretty much just the three stations in CA, Spain, and Oz. But back then it was truly globe-spanning
|
|
Dan Maloney 3:06 PM
And for anyone who hasn't seen David's current setup:
|
|
Dan Maloney 3:06 PM
https://hackaday.com/2025/01/25/making-the-longest-distance-radio-contact-possible/
|
|
David Prutchi 3:06 PM
Boys don't grow up - their toys just get more expensive :)
|
|
Dan Maloney 3:06 PM
Tell me you don't live in an HOA with telling me you don't live in an HOA
|
|
David Prutchi 3:07 PM
Actually, we do, but their regulations forgot to mention antennas! I applied for permits from my township for every one of them to avoid issues.
|
|
David Prutchi 3:09 PM
Our backyard has a perfect, undisturbed view of the Southern sky too, so I get almost horizon-to-horizon coverage
|
|
Dan Maloney 3:09 PM
That's fantastic! Not a fan of HOAs myself. I'm envious of that solar aspect
|
|
Ben Wasserman 3:10 PM
How much do you notice polarization changes on you from randomly polarized sources? I've heard the atmosphere tends to circularly polarize, but randomly.
|
|
Ben Wasserman 3:11 PM
Aka, from a source that doesn't already have a circularly polarized antenna.
|
|
David Prutchi 3:14 PM
Well, the deep-space probes all use circularly-polarized antennas, and that's where I would notice a dB up or down. I haven't really looked at polarization from linear or random polarization. However, there is some interesting work that Scott Tilley (VE7TIL, skyriddles.wordpress.com, X: coastal8049) with his polarimetric setup
|
|
David Prutchi 3:15 PM
*is doing
|
FedX 3:16 PM
I came across this NASA radar probe the other day, and I am curious, have you ever thought about dish deployment in space for communication? https://www.youtube.com/watch?v=RLw3veKBqo0
|
|
David Prutchi 3:18 PM
Thanks for the link. I'll check out the video.
|
|
FedX 3:20 PM
Of course! It was a seriously cool mechanism!
|
|
David Prutchi 3:20 PM
I'm not sure about the cost/benefit for a nation state to park a communications dish in space since the atmosphere doesn't cause much attenuation at the microwave frequencies used, so it's much easier/cheaper to point and maintain a large earth-bound dish than in space.
|
|
David Prutchi 3:21 PM
I was chatting earlier with Ben Wasserman about laser use for deep space communications with high bandwidth. Maybe there being outside the atmosphere may be worthwhile. Ben?
|
|
FedX 3:22 PM
Ah, that makes sense. I was more asking about if you had considered dish deployment for deep space probes to maintain radio contact longer. Sorry if I misspoke that.
|
|
bashcypher 3:24 PM
Do you have examples of the signals you pick up? Files on google docs or youtube? How do you de-modulate them? Would a logic analyzer convert to binary? I only see the article on your set up, if there is a link to a blog you maintain or etc I'd love to read up.
|
|
Ben Wasserman 3:25 PM
Atmosphere sucks for lasers. I think for RF, bigger antennas on the ground is way easier.
|
|
David Prutchi 3:25 PM
For amateur purposes, whenever we want to find undisclosed tracking elements we do what the big boys do - monitor from different parts of the globe to get continuous coverage.
|
|
David Prutchi 3:29 PM
For the few occasions when we can demodulate and decode we set up a shared drive to place data so that we can have coverage. This was done for example when STEREO-A probe had its “inferior conjunction” with Earth which brought it as close as 9 million kilometers, which was sufficient to receive a signal with our "small" dishes that could be turned into images.
|
|
Dan Maloney 3:33 PM
How do you know what probe you're monitoring? I suppose for some that location is a dead giveaway, if you're pointing at Jupiter it's probably Juno, etc. But what about more crowded places like everything whizzing around at L2? Do the signals have some sort of identifiers?
|
|
David Prutchi 3:37 PM
The spectrum is channelized, so you definitely know the source. It used to be easier to know the exact frequency that is being used when a probe actively communicates with the DSN network because the exact frequency used to be published, but after a cybersecurity analysis NASA stopped placing those details in real time
|
|
David Prutchi 3:38 PM
Doppler is also a dead giveaway
|
|
David Prutchi 3:39 PM
Doppler can be calculated from the ephemeris data that can be downloaded from NASA JPL’s HORIZONS System.
|
|
David Prutchi 3:42 PM
PstRotator by Codrut Buda YO3DMU, which is the software that I use to track targets makes it really easy. It has a DSN feature which automatically downloads ephemeris data straight from NASA JPL’s Horizons and uses it to control the rotator. It also gives the expected frequency for Rx that takes into account the Doppler for my specific location
|
|
David Prutchi 3:44 PM
By the way, details on my station and experiments are available at https://www.prutchi.com/wp-content/uploads/2023/11/Amateur_DSN_Prutchi_2023.pdf
|
|
Dan Maloney 3:44 PM
I was going to ask what degree of automation you have on your station -- seems like a lot of observations might need to be done while you're doing IRL stuff like work and family
|
|
David Prutchi 3:47 PM
Tracking strong-signal sources is not much of a problem running on automatic. However, tracking weak sources like Juno requires constant tweaking of the antenna.
|
|
Thomas Shaddack 3:50 PM
Could the tweaking process be automated? Leveraging eg. tricks military tracking radars use?
|
|
David Prutchi 3:50 PM
I like building the equipment and getting it tweaked a lot more than collecting data over long periods of time, so for me it's more of a weekend activity. There are occasions when timing is critical, so I do have my system set up so that I can control it remotely
|
|
David Prutchi 3:54 PM
Yes, tweaking could definitely be automated. I do use, for example, geostationary sources to calibrate the rotator. With my system I need a calm day to track because the amount of play that I have during a windy day makes it next to impossible to maintain constant tracking to within .5 degrees or better.
|
|
Thomas Shaddack 3:55 PM
Could other sources be used? Jupiter? Sun itself could be handy for checking the antenna, scan over it and see if it is round as it should be.
|
|
David Prutchi 3:59 PM
Absolutely! Sun and moon noise are great. That's the main way we compare setups and evaluate performance. You are absolutely right about the use of the Sun and moon to look at the beam profile, especially at the lower frequencies. Jupiter is a very powerful emitter at HF, but I don't think it generates much narrow-band signal to use as a calibration source in the x-band |
|
Dan Maloney 4:01 PM
Lots of action on the Moon these days with all those private landers. I know it's not very far away, but are there any special challenges listening in on lunar surface missions?
|
|
David Prutchi 4:03 PM
Those are easy. In fact, with the landers you can listen in on both sides of the conversation with Earth stations because the signal from Earth bounces on the Moon's surface. Now, "listen in" is a relative term ... we can easily see the signal's carrier, but demodulating and decoding it is a different story
|
|
Dan Maloney 4:04 PM
That's pretty cool. Kind of the RF equivalent of "Earthshine"
|
|
David Prutchi 4:06 PM
Yes. My favorite mode as a ham these days is EME (earth-moon-earth), for which I use the 3.5m dish and 500W (at the feed) at 1296 MHz.
|
|
Thomas Shaddack 4:07 PM
Could a moon bounce be done with a microwave oven magnetron, assuming all we want to see is on-off modulated carrier wave?
|
|
David Prutchi 4:12 PM
I've often wondered about that... the signal coming from an oven magnetron wobbles all over the place, so maybe using the magnetron with a stable power supply and locking it against a known frequency source. This is because the return signal is pretty weak, so you don't want to be spreading the energy all over the place (and trying to keep up with it + doppler + libation).
|
|
David Prutchi 4:12 PM
In addition, 2.4GHz at the ISM frequency used by a microwave oven is crowded with a lot of very noisy sources.
|
|
Thomas Shaddack 4:13 PM
Or, alternatively, we could sample the signal from the magnetron as it comes out, and use it as FMCW modulation for detecting the returning pulse as we know what modulation we are looking for in the returning signal?
|
|
David Prutchi 4:14 PM
EME however is possible with WSJT and a very modest station (10W into a 65cm dish at 1296MHz)
|
|
David Prutchi 4:15 PM
I just Googled using oven magnetron for EME and this discussion came up: https://www.dxmaps.com/discuss/oven.html
|
|
Dan Maloney 4:16 PM
I mean, it worked for E.T.
|
|
David Prutchi 4:19 PM
:)
|
|
Thomas Shaddack 4:19 PM
Oh sweet!
|
|
Dan Maloney 4:19 PM
So, we kinda blew past our alloted hour, sorry about that. David, we'll let you go if you need to get back to life, I really appreciate your time today. Or, feel free to stay on and keep the conversation going, the Hack Chat is always open
|
|
Thomas Shaddack 4:20 PM
...thought... bounce the signal modulated with slow-scan tv image of buttocks, for ultimate mooning.
|
|
David Prutchi 4:20 PM
Thank you. I do have to return to real life with a conference call in 10 minutes. Thank you very much Dan for the invitation and to everyone who participated. 73 de N2QG!
|
|
Dan Maloney 4:20 PM
lol
|
|
Thomas Shaddack 4:21 PM
Work is a four-letter word!
|
|
Boian Mitov 4:21 PM
Thank you @David Prutchi and @Dan Maloney :-)
|
|
Thomas Shaddack 4:21 PM
Thanks, was fun!
|
|
Dan Maloney 4:21 PM
73 back at you de N7DPM. Thanks David, and thanks to everyone for the great discussion!
|
Discussions
Become a Hackaday.io Member
Create an account to leave a comment. Already have an account? Log In.
https://www.prutchi.com/wp-content/uploads/2023/11/Amateur_DSN_Prutchi_2023.pdf
It's returning Page not found, I am trying to reach it just couple of minutes after the chat, why it is not available?
Are you sure? yes | no
The link worked for me just now, are you still unable to access it?
Are you sure? yes | no