A 24/7 H-line station on an old Android phone with HydraSDR and DD Feed
Ayushman Tripathi
Hi all,
I had a spare OnePlus 11R lying around, so this weekend I turned it into a radio astronomy node, and it is now running 24/7 with my 0.9 m WiFi grid dish and the HydraSDR in the same Urban RFI setup that I was trying to fix. Some of you have seen the live feed on my site, that panel now comes from the phone.
The bootloader is unlocked and rooted with Magisk, then a full Debian 13 in a chroot on the phone, so it is a normal Linux box with apt. numpy, scipy, matplotlib, astropy and virgo installed from Debian packages, no fighting with builds. The HydraSDR host tools compiled on the phone. The SDR sits on a USB-C Thunderbolt hub that also charges the phone, and as root, the software opens the SDR directly, no Android permission popups. The observing loop is the same one my laptop ran: 5-minute scans, 1024 channels, 5 MHz, bias tee on, max gain. Every plot lands in the phone gallery, and the site pulls from the phone. A watchdog restarts anything that dies, and it comes up by itself after reboot, and Android's background killers are switched off. So far it has not missed a scan.
Attached is the pic of the setup, the afternoon spectrum, and a shell capture of the node running.
Two things I observed:
1. The H line shows in most single 5-minute scans, even at noon, pointing well off the plane (3 to 4% above baseline at galactic latitude +15). When I moved the dish onto the plane tonight, it went to about 10%. The 5-minute plots show the two velocity components you expect in that direction.
2. The phone gives a much cleaner spectrum than the laptop did with the same dish, feed, SDR and gains. I compared old laptop scans with the phone scans using the same analysis: the baseline ripple is 3 to 5 times smaller on the phone, and the channel noise is close to the thermal limit, where the laptop was several times above it. To be clear, it is not that the phone has fewer spurs, it has a few more. What got better is the floor. My guess is dropped USB samples on the Windows laptop plus a ground path through the laptop's mains supply, and I will test both and post the results. I don't exactly know why, but I'll test this more.
I will share more observations as it collects them. Happy to answer questions if anyone wants to try this with a spare phone.
You can watch this one live at: https://radioastronomy.in (The RFI comb spikes that it shows now are due to the current pointing towards a bunch of buildings, as it's an urban place full of RFI, but it doesn't get those if pointed in the opposite direction like the plot I shared with the same system from this afternoon, but currently there's not much H1 there.)
Also, the feed from the 2.4 m dish is offline for a few days due to a cellular network issue in the region because of heavy rainfall, which is expected to be fixed in a few days, and then the site will auto come back live.
Thanks
root@localhost:/# lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux 5.10.236-android12-9-o-g74d132f4467adummy_hcd Dummy host controller
Bus 002 Device 001: ID 1d6b:0002 Linux 5.10.236-android12-9-o-g74d132f4467a xhci-hcd xHCI Host Controller
Bus 002 Device 002: ID 1d50:60a1 www.hydrasdr.com HYDRASDR
Bus 003 Device 001: ID 1d6b:0003 Linux 5.10.236-android12-9-o-g74d132f4467a xhci-hcd xHCI Host Controller
root@localhost
OS: Debian GNU/Linux 13 (trixie) aarch64
Host: Qualcomm Technologies, Inc. Cape MTP, Udon
Kernel: Linux 5.10.236-android12-9-o-g74d132f4467a
Uptime: 13 hours, 50 mins
Packages: 483 (dpkg)
Shell: bash 5.2.37
CPU: cape (8) @ 3.00 GHz
Memory: 5.19 GiB / 7.06 GiB (73%)
Alfred Aburto
Nice HI galactic hydrogen spectrum from a small grid dish antenna!
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Ayushman Tripathi
Ayushman Tripathi
Hi,
Some progress on the android phone node with more data. Attached is a full day of sky from it, 3 days of 5-minute scans at one pointing stacked together. Both galactic plane crossings show up where they should for that pointing, the strong one toward Cygnus and a weaker one on the other side, and you can see the Perseus Arm behind the main peak. Also attached is the same data as a heatmap and one of the single scans.
The same dish, DD feed, SDR and gains that were an RFI mess on the laptop just work on the phone, it sees the line even off the plane, so I am dropping the plan of trying to add a filter before the LNA, no need for it now.
I also ordered a DiSEqC H-H motor, for azimuth, and a linear actuator for elevation. An ESP32 drives both, it sends the DiSEqC commands over the coax with a small LC circuit, and a compass module tells it where the dish is actually pointing (just need to see if the compass can survive the motor and metal near it). The phone's code tells it where to go, so it can track something, or I can just point it from software. The beamwidth of the 1 m grid is not very narrow, which helps in some pointing tolerances here.
Photo of the motor attached. Will share the build as it progresses.
Thanks
bsn...@gmail.com
Ayushman Tripathi
On 13 Sep 2026, at 06:04, bsn...@gmail.com <bsn...@gmail.com> wrote:
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