Kraken SDR antenna base and placement template
Description
This is a design for 1) a mount that will carry the set of five antennas sold for the Kraken SDR receiver and 2) a template for placing the antennas on a car roof or similar. The design consists of a central hub and five detachable arms with holes for precise positioning of antennas at different radii. The arms are dovetailed into the hub and can be held in place with a rubber band or string placed around pegs on each arm. 1) In the antenna mount version of the design, the magnetic antenna bases are attracted to steel washers mounted into holes on the underside. Cables can be held in place by simple cable guides on the arms, and by twist ties through holes in the hub. Mounting holes for the array are provided in the hub. Velcro may also be a good way to attach the mount to a flat surface. The steel washers placed in holes on the underside are most easily held in place by a strip of packing tape. 2) In the template version of the design, arms are thinner and thus slightly flexible for placement on a curved car roof. The holes are semicircular at the edges of the arms. Then the template can be rotated away and removed after placing the antennas, as illustrated in a photo. The geometry is such that the holes are rotationally shifted around the center of the array in order to have the correct radius from the center. As a consequence, the side of the arm is not an accurate representation of the pointing direction of an antenna relative to the center. The correct direction is indicated by grooves in the top surface of the arm starting next to the hole being used (colored in blue un the upper arm on the photo). On a car roof, the array should be laid out such that the groove next to antenna 0 is parallel to the driving direction. The template version generates a thinner hub, but alternatively the hub for the antenna mount can also be used for the template, as shown in the photos. OpenSCAD source code is provided so that the design can be adapted as needed. Dimensions are determined by parameters at the start of the code. See comments in the code. The number of radial positions, and thus the length of the arms, is set by npositions. The part to be rendered is set by render. You may want to set the value of dwasher to the diameter of the steel washers you use for attracting antenna magnetic bases, or change dfoot to fit a different antenna type. If you are unfamiliar with OpenSCAD, here is how: 1) Download, install, and run OpenSCAD. 2) Open the KrakenAntenna.SCAD source file. 3) Press F5 to preview (rough view, may be slow). 4) Scroll down to look at the parameter values in the code and the comments. Change the values as needed. 5) Press F5 to preview again. 6) Press F6 to render the final shape (final view, may be slower). 7) Press F7 to export the new .STL file. The design is set up to give a 1 mm gap between the inner end of the arm and the bottom of the dovetail slot. Depending on the accuracy of your printer, the actual width of this gap may be different when arms are inserted. If you want to correct for a printer inaccuracy, change the parameter slotadjust to adjust the width of the slots in the hub by the chosen amount. As a guide, if the width is reduced by 0.1 mm (slotadjust=-0.1;), the arm will fit 0.3 mm closer to the center (for the default dovetail angle of 10 degrees). STL files are provided for base and template arms with antenna radii up to 350 mm. The disassembled base and template becomes a compact package. Photos show how the complete Kraken, antennas, base and template can fit in a small plastic case for transport. Also shown is a set of arms in different lengths. The case shown contains an andriod tablet which has a 3D printed cover for protection. This cover design is provided as STL and OpenSCAD files.
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