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.

Execute the Radio Meteor Observations program on mac os

MeteorLogger Screenshot
MeteorLogger Screenshot

What is it about

Wolfgang Kaufmann wrote an impressive article and even a more impressive software for the hobby radio astronomers. I highly recommend checking out the article and play with the software as there are not so many radio astronomers among the community. His software is written in python with a very clean UI. It directly connects via the computer sound card and grabs the audio signal. I shortly describe here what to install on a Mac OS to get his software up and running.

Where to get it

The software can be downloaded at http://www.ars-electromagnetica.de/robs/download.html. Unfortunately it is not available on any online repo like github but the source code can be downloaded as a zip file.

Preparation

The PyAudio package needs some libraries and direct access to the os sound system. Therefore we need it install this audio package outside of python itself

The necessary python libs can be installed via pip. I recommend doing it in a virtual environment

That is all. After installing the python libs the program starts right away

 

Setting up SDRplay remote on a raspberry pi

SDRplay
SDRplay

SDRPlay

I recently bought myself a SDRPlay receiver to play with this technology and maybe build a ground station or meteor scatter detector. The original plan is to setup a receiver on the Motionlab roof with an raspberry pi and send the IQ data via network down to a local server and extract the interesting information. One great software to work remotely with an SDR receiver is the Soapy project.

Install the raspberry pi part

Build system

Install the latest raspberry pi lite version from raspberrypi.org

Core system

The soapy part consist of 3 parts. The Core system must be installed first.

SDRplay

The SDRplay part consist of two parts one are the proprietary binary libraries from SDRplay itself the the other part is the soapy wrapper for SDRplay.

Binary Libraries

The driver can be downloaded from the SDRplay homepage https://www.sdrplay.com/rpi2dl.php

The SDRplay Soapy wrapper

Test the Soapy access

Soapy Server for Remote Access

Run the server

If you want to run it as a service have a look here on how to autostart stuff in linux.