An article in IEEE Spectrum describes how an amateur astronomer constructed a pyramidal horn antenna using a $25 roll of roof flashing and an emptied paint-thinner can to detect the 1,420.4 MHz radio emissions from neutral hydrogen clouds in the Milky Way.
The receiver chain consisted of a Nooelec SAWBird+ H1 low-noise amplifier with a standing-acoustic-wave filter centered on 1,420 MHz and an RTL-SDR V4 software-defined radio dongle.
Using the planetarium program Stellarium, the antenna was pointed at galactic longitudes of approximately 15, 30, 45, 60, 75, and 90 degrees in the galactic plane to sample hydrogen clouds at different distances from the galactic center.
The SDR# software with an IF Average plug-in stacked several minutes of data to produce spectra showing the Doppler-shifted hydrogen line; the largest redshift in each spectrum was taken as the tangent-point velocity for that longitude.
Microsoft Excel was used to model each spectrum as a sum of bell-shaped components, extract the maximum redshift, and convert those values into orbital velocities and distances using the tangent-point method and trigonometry.
The resulting six data points showed orbital velocities that did not diminish with distance from the galactic center, matching the general shape of the rotation curve published in a 2023 paper in Publications of the Astronomical Society of Japan.
Two innermost points fell below the expected curve; a second curve-fitting attempt brought them closer but they remained somewhat off, a limitation noted by the author.
The author concludes that the flat rotation curve observed with this backyard instrument is a basic signature of dark matter's gravitational influence on the Milky Way.
Detect Dark Matter’s Mark From Your Backyard
This is an independent summary. The complete reporting, supporting context and any primary documents remain with IEEE Spectrum.