On the 29th May cosmonauts, Oleg Kononenko and Flight Alexey Ovchinin, undertook an EVA (spacewalk) outside the ISS to retrieve science experiments, install some new handrails and conduct some other routine maintenance. Numerous successful observations of the EVA were captured by ground stations on the network and you can listen to the EVA communications. This post on the Libre Space community forum has links to all the observations.
Antenna Types Comparison
SatNOGS legend Corey Shields has begun some comparative work on antennas. Corey is using the same location and the same observations to test directional ax/el yagi, a fixed low-gain yagi and finally a discone. It’s interesting work and Corey is posting his results and discussion here.
SatNOGS community has been busy over the last couple of months, with many exciting updates on projects to share with you!
First and foremost, the 3.1 version of the SatNOGS rotator is soon to be finalized. If you are already working with a v3 keep in mind that upgrading to 3.1 is pretty straightforward, on the meantime feel free to share your build progress or finished ground stations with our community We got have some stickers to send to SatNOGS ground station operators. We really hope that lot’s of people get to install their own v3.1 rotator and hook up to the SatNOGS network, and we are working on a way to get the v3.1 rotator design to as many people as possible.
Our crowd-sourced satellite database, SatNOGS DB, is expanding and will soon be powering Csete’s gpredict through it’s API. In the meantime we deployed new functionality that allows SatNOGS DB to visualize telemetry data captured using the SatNOGS Network of ground stations.
We really appreciate people participating in the SatNOGS project, either in our community website, our IRC/Matrix chatroom, the SatNOGS Wiki, populating the SatNOGS database and our source code repositories but we also enjoy meeting people interested in SatNOGS in person.
Last week on Linux.conf.au taking place in Hobart,Australia, Scott Bragg’s gave a great talk titled “Decoding Satellites With SatNOGS“. It was a great overview of the SatNOGS project and the ways you can get involved.
Since most of the core SatNOGS team lives in Europe most of us will attend FOSDEM in Brussels,Belgium this February. There Manolis Surligas is giving a talk “SDR for Space the Open Way” focusing on the Software Defined Radio RF frontend and the GNU Radio module operating it and will be introduced in the coming versions of the SatNOGS client.
Stay tuned for more detailed updates, and as always … keep hunting satellites!
An important part of the instrumentation of our ground station is the Antennas. Early on the SatNOGS team designed and constructed 2 Yagis for UHF and VHF bands. The UHF Yagi design was essentially a cross Yagi design trying to address the circular polarization issue. Based on the experimental operation of the ground station we were sure we can do something better.
Satellites are tumbling and turning, thus if the transmission of the transponder is done in a single dimension polarization you better match this polarity to get the optimum gain. (if not you will loose 30dB) (check here for details). We decided that a Helical antenna would give SatNOGS a better chance for an optimal reception, so we needed to design, document and build one.
There are a couple of theoretical models for Axial-mode Helical Antennas. Most notable are the Emerson one and the Kraus. We decided to go for Emerson, given our wavelengths, construction constrains and overall size. As we were going for UHF band 437Mhz seemed like a popular frequency for satellite communications and we centered around it. As for the circular polarization we designed a Left-Hand one (as we already had a Right-hand cross-Yagi design).
Dimitris worked on a modular and extensible design that can be used on other bands too. 3D printed parts and off the self items is the classical recipe that we followed. The result is a sturdy and easy to construct antenna. Initial tests are showing improvements compared to our cross-yagi UHF which is a win!
The design can be found here, bill of materials here and a detailed documentation on how to build here.
Optimization of the antenna is crucial. We invested considerable amount of time towards that and there is always room for improvement in matching, constructions and details . More NEC calculations will follow and we expect more fixes as we go.