Big DK3 HF Mobile Screwdriver Antenna
Description
Back in 1991 there was a design for an HF mobile screwdriver antenna created by D.K. Johnsson, W6AAQ. It used a motor/gear assembly from a small electric screwdriver, some PVC, wire and pipe to form an antenna. This was called the Big DK3 antenna. This project is a modernized version of the Big DK3 using some 3D printed parts I created based on the original drawings. It should be noted that this is still a work in progress so please don't start printing things just yet. I am close to a working product though so I'm expecting to update this thing with build instructions and finalized parts soon. The remote control is based off of two Arduino boards. One Nano in the control box and a Pro Micro in the antenna base. The firmware is mostly done, just working on some final tweaks. Then I need to design the box for it. More to come on this. There is the main coil form. It has the grooves for the windings. On top it has the threads for a 1/2" MIP to 1/4" FIP brass bushing. That's where the antenna whip and ferrule will attach. The coil wire is lead into the area through a small hole at the top of the winding and is clamped down on by the bushing. At the bottom there is a similar hole leading al the way to the bottom of the coil form where the wire can be secured with a screw. A hole runs through the length of the coil form, off-center and is meant fr a guide rod which will prevent the coil from spinning. In the bottom center are threads for the rod that will attach to the motor assembly and move the coil up and down. There is a custom motor mount disc meant for the motor/gear assembly from an old Black & Decker VP840 cordless drill. These can still be found on eBay for affordable prices. If your motor is from a different device you will need to create a mount for it. You may be able to use mine as a template. I experimented a bit with the coil contacts and came up with the insert included here. It sits inside the outer metal pipe, at the very top and has spring contacts made from thin copper tape. Those spring contacts touch the coil in several places to ensure good contact. I also designed a shroud that will attach to the top of the metal pipe and will cover the coil as it travels up and down. A whole at the top has a grommet which allows the antenna whip to come through. That grommet should be printed in a flexible filament like TPU. A complete bill of material will be included once the project is completed. 1/19/2021 - Added the PDF that this build is based on. It has a lot of good information. 1/26/2021 - Update: The spring contact insert part is no longer needed. I ended up going with the Berylium Copper finger stock 0078001402 from [surplussales.com](https://www.surplussales.com/rf/RFFingerstk-1.html). With the [pipe I used](https://www.homedepot.com/p/2-in-x-10-ft-Electric-Metallic-Tube-EMT-Conduit-101592/100400411), I cut a length with 17 contacts and it fit nice and snug inside the pipe. The adhesive on the back of the large lip on the contacts holds them in place. 2/2/2021 - Update: An updated version of the bottom insert has replaced the old one. This new version (still named v2) has a slightly larger slot for the cord to the USB breakout board. This allows for a 5-pin header connector to be inserted. It allows the USB breakout board to connect using 5 pins rather than having to be soldered. 2/5/2021 - Update: A few additional changes have been made to the bottom insert. Mainly the addition of a support for the nut holding the SO239 stud so it is easier to tighten it. Also adjusted the slot for the USB cord so it will fit the [micro-USB breakout board](https://www.amazon.com/gp/product/B07W844N43/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1) I have. Along with that I also included a cover for the USB breakout board that attaches with 2 screws through the breakout board to the bottom insert. 2/14/2021 - Update: I added a version of the bottom insert without the holes for the USB connector, just in case someone wants the antenna without that connector.
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