Live H line feed from my homebuilt radio telescopes
Ayushman Tripathi
Hi all, I have put my radio telescopes online so anyone can watch the hydrogen line live. It is at https://radioastronomy.in
The main one is a 2.4 m dish at a remote low RFI site, streaming the hydrogen line spectrum and waterfall every few minutes as the sky drifts through. The dish is fixed so the galaxy crosses twice a day, and you can watch the line come and go live. Attached SS is from today's crossing.
Also there is a 0.9 m WiFi grid dish + DD Feed running its own H-line loop and a Ku dish doing a narrowband drift survey. The same 2.4 m data feeds an amateur SETI search. Next I want to put up a live hit list of any transient caught by any of the three.
It has a lot of bugs still, which I'll try to fix this week.
Also, I'm still investigating the 1421 MHz interference I posted about last week, working through the satellite candidates. If it was 2023-003E, then it probably does not cause the interference all the time, maybe only when it is downlinking to a ground station. I tried to catch it once, but the pass was in eclipse, on the night side, so it may not have been transmitting. Will try again on a sunlit daytime pass soon.
Thanks
Alfred Aburto
Good job, Ayushman! I like it! :-)
Can you explain the structure of the galactic 1420.4 Mhz H1 line? I'm trying to visualize what is causing the structure. H1 gas clouds blue and red shifted. There is a bump on the right side (gas cloud closing in on us).
What does the H1 line look like at 1Mhz BW?
Thanks!
Al
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Ayushman Tripathi
Hi Al, thanks! Yes, the bump on the right is gas coming toward us. Attached is a galactic map showing each signal's origin.
The beam was at galactic longitude 56, looking into the inner galaxy.
Main peak near 0 km/s: local gas in our own spiral arm, about 1,300 light-years away.
Left shoulder, about +20 km/s, receding: the Sagittarius arm, about 6,000 light years out.
Your bump on the right at 1420.75 MHz is about −66 km/s, approaching. At this longitude everything inside the Sun's orbit appears to move away, so approaching gas has to be outside it (as you can see in the attached diagram, I can try to add this live diagram also to the website this weekend).
That puts your bump about 50,000 light years away, in the outer galaxy on the far side from us. For scale the whole disk is about 100,000 light-years across, and we sit 27,000 from the center, so that bump is gas on the opposite edge of the galaxy. Easily the most distant thing in the spectrum.
1 MHz is about ±105 km/s, so it catches all three of these. The site shows topocentric velocities, I applied the +7 km/s LSR correction here.
Thanks
Alfred Aburto
Thanks for the galactic view! Makes sense!
The spectrum looks pretty continuous. I mean, if you did a higher resolution FFT, there would be no additional structure or "bumps" show up?
It's interesting that the doppler shifts say a lot about the structure of the galaxy even though the spatial resolution is not that great.
So, if a radio telescope was at a different Earth latitude, pointed at a fixed location in the sky, it seems that the spectral shape of the the H1 line would shift. Correct?
Al
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Jim Sky
Jim Sky
Ayushman Tripathi
Hi Al, thanks!
On resolution, I can show you. The plot on the website has 0.6 km/s channels, but the same capture also gets a 2^20 point FFT for the SETI search, 2.861 Hz per channel, about 350x finer.
Attached is this night's crossing at that resolution. Same three bumps, same shape, no new structure. The grey is noise, 4.8% per channel, exactly what 150 seconds predicts. The few narrow spikes are internal/external spurs.
Yes, the same RA and Dec mean the same gas and the same shape. As per my research, Earth's rotation adds under 0.5 km/s depending on latitude, which the LSR correction removes.
Ayushman
Ayushman Tripathi
Alfred Aburto
Hi Ayushman,
I like your live feed!
I was just looking at it and I noticed (well, I assume) your main
beam axis is pointed at the Sky Map place with the green circle
with a plus sign in the middle. It is pointed, apparently, outside
the galaxy and you were still getting and H1 signal. Is that
normal?
Can I ask what country you are in?
Thanks for doing the finer resolution FFT. No finer detail seen.
The 1 million point FFT is great for the SETI search. Are you with a group doing the SETI search? I remember the SETI League.
On your SKY MAP can you add a time of day?
You know I am 84 years old and would love to do a SETI search as my last project. I read the book "Probability 1", by Amir Aczel, and I think he is right. There is other life out there. Intelligent? Well, that is uncertain. Going from bacteria to cells with a nucleus and mitochondria seems to be a chasm that may not be crossed except very rarely. But scientists still have a long ways to go to figure out the whole process, so in the mean time, do a SETI search in the water hole region. :-) I've always liked that idea.
Al Aburto
San Diego, CA
32.81444N, 117.13639W
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Stephen Arbogast
Liam Siddall
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Shaik Samad Pasha
Hi Ayushman,
Great work!!
I have a few questions. I noticed that these are live HI observations and that the profiles are being calibrated in real time. How are you doing the calibration? Are you taking a separate time slot for recording the background/reference for calibration?
I had tried a similar real-time calibration approach earlier with temperature calibration, where I converted the arbitrary units into temperature units, but I used to face problems in getting a good calibrated profile for longer observations. So, I used to take cold and hot readings around 4-5 times a day to account for changes over time.
Just wanted to understand how you are handling the calibration for these observations.
Best,
Samad
Ayushman Tripathi
Hi Al,
Yes, seeing H1 with the beam outside the arms is normal for a 2.4 m dish at a low RFI site. Hydrogen is everywhere in our galaxy, not just in the arms, we are sitting inside it, so even off the plane there is some. Even now in the attached image, you can see that H1 is still detected even when the dish is not pointed at any arm. I tried one day pointing the dish randomly, wherever I pointed it, mostly I saw the bump, very small, but it was there.
That is because of the extremely remote site and the dish being 2.4 meters. The same does not happen with a smaller dish at a high RFI site, you can see the live feed of the 0.9 m dish too, but it sees nothing most of the time because of RFI.
Yes, I'm running this 2.4 m system at a low RFI site on the roof of my grandmother's home in central India. Not many houses are nearby, only farms, cows, and forests, which don't generate RFI :) But because of that, I can't be physically there always. That's why I use a cellular LTE router (as there's no 5G at that location) with an outdoor antenna, so that's how I'm able to get that data. I visit there once every 2-3 months to repoint the dish and fix any failing components. The #1 failure point is the smart plug I am using to reboot Raspberry Pi 500 if it gets hung or something. The Pi is running this setup with an Airspy Mini on it (which I'll replace with a HydraSDR to try when I visit next).
By now, in ~1 year, for some reason, 4 of these "not so smart" plugs :) are fried, maybe by temperature or voltage fluctuations or randomly. Pi uses a 15-hr backup battery for power backup, as power is not reliable in remote regions, a single storm can take power out for 1-2 days. Next, I'm thinking of getting Sonoff smart plugs to try them. The other option can be a hardware watchdog, which I'll also consider, but a smart plug was an easily available option.
The next upgrade for this system will be to engineer a remote dish-pointing adjustment system using cheap linear actuators that I see available on Amazon, etc., which I'll think about in the future.
For my KU system I run it on the balcony of my home, as normal urban RFI doesn't affect KU much, my smaller H1 dish, the WiFi Grid with DD feed on the same balcony is overwhelmed by RFI, but during rare occasions of widespread power cut or on some nights, 3am to 5am, I was able to get good enough H Line data during that time, which I posted here, but otherwise normally it's overwhelmed by RFI. I'm planning to move this small dish to the same location as the 2.4m dish, as fighting RFI here is turning out to be difficult, and it'll work there much better without any RFI, but I also wanted to keep a system near me :), The other option is to use a cantenna + Sawbird instead of DD feed for my smaller dish because there's no way to put a filter before the LNA on the complex integrated Discovery Dish feed (at least I can't find one), but for this, I need to get the custom cantenna support arms fabricated for the WiFi Grid Dish. Anyways, I'll think about this in the coming months. I'm also thinking about setting up a radio telescope at a low RFI site in the UAE, in collaboration with an educational institution there. I plan to visit their radio astronomy observatory in Sharjah later this year while visiting the UAE.
I'm doing SETI individually, without a group, yes it seems the Amateur SETI League project Argus was brought to an end. I did reach out to the SETI Institute, California. They were kind enough to send me a few resources and some support options, but they told me they are not running an amateur SETI programme currently, but yes, a group doing it will be really nice.
Also a fun fact, the server which is running the website is just a Pi at my home :), you can see its image attached here. It's just connected to free Cloudflare Pages, as hosting wasn't cheap long-term.
I added the time of the day in Pacific Daylight Time on the map. Thanks for the feedback.
Yes, I think a SETI search is a great project, and I would be glad to help you set one up for sure. The odds are low, but for sure it's worth the attempt, and the process itself is very fascinating and inspiring. And I would not call it your last, I read Frank Drake was still at it in his nineties :)
Thanks.
Ayushman Tripathi
Hi Stephen,
Yes, nice idea, but storage is not cheap, if it were, I would save it for sure. For now I'll upload anything unique and monthly data on Zenodo. CERN says they will keep those for decades at least, so that is my million-year plan :)
The raw data off my 2.4 m dish system is 12 MB a second, the free space on the Pi's SD card would fill in about 18 minutes, so the raw IQ gets thrown away and only the integrated spectra are kept. I did try an external SSD, but it generated a lot of RFI, so I had to use a cheap HP microSD card, and every write to it is a countdown :), On my home Pi I did find an external HDD that creates far less RFI than a SATA-to-USB SSD, I'll try that HDD for 2.4m dish system soon.
Also there's the GitHub Arctic Code Vault, which should have much better odds of surviving if GitHub continues that, even if humans continue to get into wars :)
Thanks
Ayushman Tripathi
Hi Shaik,
Thanks! My calibration is shape-based, not temperature. I divide each observation by a reference bandpass from the same receiver, so the y-axis is percent above the reference, not kelvin, with no hot or cold load.
The reference is a 50-ohm terminator on the LNA input or cold sky, 5 minutes at the same gains. I take it once, and it stays stable for weeks. I have tried both, and for me the difference between them was not significant.
Please check the attached diagram.
Thanks
Ayushman Tripathi
Hi all,
After a recent conversation with a member here, I realized the real barrier for most people who want to try Amateur SETI is not the dish or the SDR, it is the software. Right now my SETI survey software is a bunch of scripts running on Raspberry Pi 500, and you need Linux and the command line to use it.
So I'm building an OPEN and FREE GUI version of it for amateur SETI. You install it, select your SDR, enter your dish size and pointing (later I can integrate it with Stellarium), and it runs on its own and shows the waterfall and the hits and also does H-line plotting on the same data captured for SETI similar to the one I've run on the website: https://radioastronomy.in/.
It will be open source and free, where all can fix the bugs and make it better, and I'm thinking of publishing it on the Microsoft Store too as I think it's free to publish, so on Windows it's a normal install. Raspberry Pi/Ubuntu will be supported too.
It will take a few weeks.
Thanks
Alfred Aburto
Awesome, Ayushman!
Al
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