We need an Antenna
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.
|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.
and this plug
The cross connection in between the 4 dipoles is the same aluminium tube with a length of 584 mm.
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.
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
We measured the dimensions with an AA-1400 and where very proud to get such a great result of 1 at the center frequency.