Lindenblad Antenna for 2 Meters DIY

We need an Antenna

Lindenblad
Lindenblad

There was need for an antenna for our SatNogs (Satellite Ground Station Network). As serious hackers there was no other option than to build one of our own. After several more or less unsuccessful experiments with several antenna types we decided to build a Lindenblad antenna for the 2 meters (144 Mhz frequency) range. We are Ronny (DL7ROX) and myself (DM1AS). There are several papers and discussions available on how to build such an antenna, most of them vom Amsat and US in general.

So I only focus here on the “translation” into the metric system and the DIY parts to assemble one antenna.  For a very good paper and the magic background please have a look at https://www.amsat.org/wordpress/wp-content/uploads/2015/08/An-EZ-Lindenblad-Antenna-for-2-Meters2.pdf.

Dipole Dimensions

Dimension Length / Distance
Length on one dipol element 373 mm
Space between the dipoles 19 mm
Total length of the dipole 765 mm

In order to make your life easier and the spacing hopefully very accurate I create this T-connector with Fusion360.


https://a360.co/2Q210Xh

and this plug


https://a360.co/2RmxR5P

The cross connection in between the 4 dipoles is the same aluminium tube with a length of 584 mm.

The wires

As we have 4 dipoles of 50 Ohm impedance in parallel and the wire typically as 50 Ohm we need to match it. The solution in the paper is to use an 75 Ohm TV wire with a defined range so it will match the 200 Ohm to the 50 Ohm of the wire impedance.

impedance matching wire
impedance matching wire
A 584 mm
B 5 mm
C 8 mm

 

Put it all together

Each dipol will be connected to one impedance matching wire and all 4 wires to the antenna wire. Don’t forget a cable ferrite on each of the impedance matching wires very close to the dipol side. The 4 dipoles will then be connected opposite to each other and each dipole rotated by 30 degrees clockwise to the horizon.

Measure the SWR

SWR-Lindenblad
SWR-Lindenblad

We measured the dimensions with an AA-1400 and where very proud to get such a great result of 1 at the center frequency.

G199 or how to 3d print a logo on existing STL files

The problem

Logo with 2 different Filaments
Logo with 2 different Filaments

Sometime you want to print you logo or some text on your 3D object with different filament but you only have a single head printer and don’t want to spend all the time sitting next to your printer to wait for the right moment to manually pause the print and change the filament. Like the Motionlab logo on the picture. For sure you could print it separately and glue it on the main printed part but specially with text it’s a lot of tiny parts to take care of and align. If you are lucky and have a dual print head it’s not a problem but there is also a way to do it very simple with a singe print head by editing the G-Code file and add G-Codes by hand.

The solution

There is a G-Code named G199. Regarding to Craftware the purpose of the code is “G199 pauses the print immediately, and moves the head to X0, Y100. (this is the command the LCD screen uses)”. So by adding this code by hand the printer stops printing and moved the head to the side. After changing the filament (and also extrude some more by hand to make sure the printer is ready) you can press “continue” on the printer display.

Prepare the SVG file

If your logo is already in SVG you are lucky. Otherwise try to convert it to SVG and make sure it’s in connected objects. If you need some geeky stuff I can recommend Geeksvgs.

Use Fusion360 to create the STL logo file

Fusion360 insert SVG
Fusion360 insert SVG

In Fusion360 use Insert -> Insert SVG -> Select SVG File to open the SVG file on a Sketch. Resize and stretch it as you like or the dimensions dictate.

Next step is to extrude the logo to a 3D object. This can be done simply by “Stop Sketching” and then press “e” for extrude. Select everything by drawing a frame with your mouse. Unfortunately fusion has no idea witch part of the logo should be extruded and witch not. Press and hold CTRL and deselect the inner parts of the logo. For example the circle in the “o”. I recommend extracting 10 mm even if you only want to rise the logo by 4 mm.

As the single objects are not connected fusion creates several bodies instead of one.

Save single STL
Save single STL

A single STL file with all Bodies included at the right position can be exported by pressing the Component name and press the right mouse button.

Combine both STL in your slicer

Now as we have two STL files we can load them both at the same time in our slicer (no matter witch one). Position your logo at the right place, scale it and change the z access offset accordingly to your needs.

Combine STLs
Combine STLs

As we extruded the logo 10 mm there is enough space to play around. Make sure at least one mm is submerged in your main body.

 

Manually edit the gcode to add the pause sequence

Find the right Layer
Find the right Layer

Now we need to find the right place in the G-Code itself. Our slicer can help us with the preview mode. The best layer is the second one after the main body is done and the logo starts to be printed.

Mark down this layer and open the G-Code in your favorite text editor. All slicers I used always make nice comments in the code to find the light position. Search for “layer nnn” and add the “G199” statement.

 

Print

Just print the G-Code as you always do. As soon as the printer reads and process the G199 comment it stops printing and moves the head to the left side. All heating settings remain the same and you can easily replace your filament and press “Continue” or “GO” on your printers screen. Happy printing.