KrakenSDR DOA Antenna Array Template (150 MHz to 1'766 MHz)

thingiverse

Print a KrakenSDR (https://www.krakenrf.com) DOA (Direction Of Arrival) circular antenna array template on any 200 mm x 200 mm 3D printer in a single print run. The template is designed for the set of 5 telescopic antennas with magnetic base supplied by KrakenRF. As a bonus I added a 3D-printable 8 mm wrench for you to tighten the 8 mm SMA coaxial connectors (and 11 mm FME in other installations). ==================================================================== Update 10 June 2023: I added two SVG files for laser printing and cutting: - SVG with text and figures for printing text and figures in a first laser run at reduced laser power. - SVG without text and figures for cuting the circumeference in a second run at full laser power. ==================================================================== The template consists of 3 parts: - Hub with 6 magnets - Arm and extension It is the Swiss knife of KrakenSDR DOA antenna templates: - It implements 7 discrete circular antenna array layout positions for actual operating frequencies from 150 MHz to 1'800 MHz (1'766 MHz being the KrakenSDR's highest configurable frequency). - It includes a scale for telescopic antenna length adjustments according to your actual operating frequency. Easy installation and repositioning of the antennas: - The hub is kept in place by five magnets on your car's roof. - Use the positioning arm's orientation to align the KrakenSDR's channel 0 to your driving direction. - Use the same single arm in 5 positions around the hub to position the 5 antennas. - No need to unscrew the coax cables while installing or repositioning the antennas: - The positioning arm is detachable from the hub and can be pulled away horizontally between the antennas and underneath the cables, even when selecting the innermost position (1'800 MHz). - You may leave the hub on your car's roof while driving, PROVIDED THAT THE MAGNETS HOLD IT FIRMLY TO THE ROOF (possibly not if the roof is curved or coated). Sanding the hub's underside my increase friction between the hub and the roof. Frequency and antenna length adjustments: - The 7 antenna layout positions (400 to 1'800 MHz) are labeled with the maximum frequency for the respective position: Use the position with a frequency label just above your oprating frequency, e.g. use layout position 1'100 MHz for your 868 or 915 MHz operating frequency. The directivity of the 400 MHz position is acceptable down to 150 MHz. - Adjust the telescopic antennas' lengths to your exact operating frequency by using the arm and the extension as a scale: Place the end of the arm's extension on top of the antenna's magnetic base and extend the telescope according to the MHz scale to the left of the arm and extension. Note: - The fully retracted ELECTRICAL antenna length is 75 mm (= one quarter-wavelength of 1'000 MHz). At this position the PHYSICAL antenna length measured from the top of the magnetic base to the top of the retracted antenna is 130 mm. - Normally, extending the antenna beyond the retracted 75 mm covers the frequencies below 1'000 MHz. Use the left-aligned scale from 1'000 MHz to 300 MHz for this frequency range. The scale is meant to indicate the PHYSICAL length of the antenna, i.e. from the top of the magnetic base to the top of the extended antenna. You will require a separate ruler for frequencies below 300 MHz. - In order to support operating frequencies above 1'000 MHz (for which even the retracted telescope would be too long) the telescope must be extended by one half-wavelength above the quarter-wavelength of this higher than 1'000 MHz frequency, i.e. to a total of 3/4 wavelangths. See https://www.researchgate.net/figure/Three-quarter-wavelength-3l-4-vertical-antenna-geometry-and-current-distribution-four_fig3_326050515 for a visualization. This shifts the signal phase by 180 degrees, but as you do it on all 5 antennas it does not adulterate the DOA measurement. Use the right-aligned scale from 1'700 MHz to 1'001 MHz for this frequency range. Again the scale represents the required PHYSICAL length of the telescope. The 3/4 wavelength telescope extension for 1'800 MHz is identical to the quarter-wavelength (i.e. left-aligned) 600 MHz extension. Parts list: - One 3D-printed pentagonal hub - One 3D-printed positioning arm - One 3D-printed positioning arm extension. Connect the extension to the arm - either by glueing it to the arm - or by a strong sticker tape on its underside, serving as a hinge when stowing. - Five 10 mm diameter / >=5 mm height Neodym magnets. Put the magnets into the hub's bores to fix the hub on your car's roof. Glueing the magnets is optional. As always I include the OpenSCAD source file for you to improve or adapt. In case you want to modify it: - Download and install OpenSCAD from https://www.openscad.org - Launch OpenSCAD and open the enclosed OpenSCAD source file (/File/Open). - Amend the parameters at the top of the file and/or modify the source code. - Save your changes (/File/Save). - Render the design (/Design/Render). - Export the rendered design e.g. as a .stl file (/File/Export/Export as STL). - Slice and print. See my other designs at https://www.thingiverse.com/thinger13/designs