Construction of the geodesic parabolic dish developed by JA6XKQ and 1.42Ghz cantenna

For the introduction of the design, please read this article [1] written by JA6XKQ. For those who are interested in the details of the derivation and surface accuracy of the structure, you can refer to [2]. Another important thing is the supporting structures such as adding supporting rods behind the dish or additional inner meshes to prevent the heavy feed from deforming the structure. See [3] and [4]. Please refer to the excel sheet from JA6XKQ's website at [5] to obtain the specific dimensions.

This is a 1.4m f/D 0.345 dish. Three L shape aluminium bar as supporting structure is attached to a stainless steel bowl. The same material is used for the feed supports and the reflector is made from galvanized wire mesh. This picture is taken months ago and the mesh is now covered with rust, I plan to apply rust converter to the surface and spray paint at the end. An alternative is to use stainless steel mesh at the beginning, but the cost will be high.

Cantenna's diameter: 14.5cm, length: 18cm, probe's distance from the back (1/3 of the length): 6cm, probe's length: I started with 0.25*λ, and it is trimmed until a good SWR is obtained with a NanoVNA. These dimensions are based off from the design from Figure 3 at [6]. If you want to determine the diameter based on your desired edge taper, you can see page 3 at [7]. To compute the dimensions of the cantenna and a choke ring, refer to the excel sheet from SETI League at [8].

A N type female connector is used to attach the copper probe. No soldering needed as there's a hole where the probe can be slid in tightly. 

References:

[1]http://www.terra.dti.ne.jp/~takeyasu/Geodesic_Parabola_Antenna_2_1.pdf

[2]https://f4buc.pagesperso-orange.fr/parabole_geodesique2.htm

[3]http://www.terra.dti.ne.jp/~takeyasu/PhotoGallery.html#new_photo

[4]https://www.youtube.com/watch?v=od2SEhq8DR4&t=11s

[5]http://www.terra.dti.ne.jp/~takeyasu/

[6]https://www.semanticscholar.org/paper/A-compact-radio-telescope-for-the-21cm-line%3B-za-21-Saje-Vidmar/e5baaf7450e0aea72e7926e1bdd75d3175f23424

[7]http://www.w1ghz.org/antbook/chap6-3.pdf

[8]http://www.setileague.org/hardware/feedchok.htm

Hydrogen Line project with 1.4m parabolic dish, Nooelec H1 LNA and RTLSDR

The 21cm hydrogen line is a spectral line produced by atomic hydrogen. Due to the abundance of hydrogen atoms and the nature of radio waves to penetrate dust clouds in our galaxy, we can study the milky way by observing the doppler-shifted spectral line. Spectra attached below are the result of multiple gaussian curves and the corresponding radial velocity of the individual peaks are then used to construct the structure and rotation curve of the milky way.

Self built 1.4m parabolic dish (geodesic dish developed by JA6XKQ http://www.terra.dti.ne.jp/~takeyasu/...) mounted on an equatorial mount used for astrophotography.

Spectra along the plane of our galaxy from galactic longitude 0 to 360 degrees at latitude 0 degrees. Radial velocities are corrected to the local standard of rest (LSR). Individual spectrum is multiplied by a constant obtained from the calibration using the S7 region's peak brightness temperature value from the LAB survey, at https://www.astro.uni-bonn.de/hisurvey/euhou/LABprofile/

Spectrum with multiple gaussian curve fitted.

Hydrogen line map from declination -60 to 60 degrees. Hydrogen column density is calculated by integrating the area under the spectrum from radial velocity -150km/s to 150km/s and times 1.82x10^18, given at https://www.cv.nrao.edu/~sransom/web/Ch7.html

Milky way structure. Data seemed to only match with the Perseus and Carina-Sagittarius arms. Most of the points are in between the Perseus and Norma arm, this is probably due to unresolved peaks in the spectrum from smaller radio telescope. Parameters for the spirals arm plot can be found on page 7 at https://iopscience.iop.org/article/10.1086/501516/pdf

Lastly the rotation curve fitted with a logarithmic curve. The rotation speed is obtained by choosing the most red-shifted and blue-shifted radial velocities in the spectra obtained from Quadrant I and IV respectively. The rotation speed are lower compared to the published data from Clemens (1985) attached, because the most red and blue-shifted peaks are often weak and difficult to detect with good SNR and hence the chosen peaks will be not be the maximum and minimum radial velocities. But the general trend can be seen clearly in the graph, a flat curve as you go further away from the center of milky way, suggesting that something is giving them extra speed and most of the mass might not be concentrated in the center. 

Rotation speed against radius figure from Clemens (1985), Ap. J. 295, 422.

Shout out to Society of Amateur Radio Astronomers (SARA) for funding this project!