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.

AstroDIY 3D printed Dobson Telescope

How to print your own Telescope

3D printed Dobson Telescope
3D printed Dobson Telescope

For the last 3 month I worked together with a very good friend of mine (Herwig Diessner aka AstroHD) on a DIY project. The idea started back at the 34c3 conference in Leipzig. Talking the topic “tuwat!” (Do something) serious we decided to 3D print a real size and working telescope. And yes we did it. Tomorrow at the “Tag der Astronomie 2018” we will present our own 3D printed Dobson Telescope.