3 days ago •
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.
3 days ago •
Using the first version of satNOGS hardware we figured out that some times due to various reasons (software, mechanical or power malfunctions) the rotator might end up in an unknown position.
At that point, the only way to resolve that situation was to manually reset the rotator to home position (pointing at the north with zero altitude). Therefore, since we wanted the rotator to operate without human supervision, we decided that an automatic homing system was crucial.
At first thought we tried an IMU, which turned out to be too noisy and affected by the rest of the systems so we ended up with a pair of opto-swithes which are manually set at the first run.
The mounts and activators of the switches are designed in a way that they remain modular and independent of the rest of the tracking hardware so that they can be fitted in previous or future versions.
Our intention is to write two homing functions in the arduino code
The first one, which is already written, is called when the arduino boots for the first time or after power loss. In this function, the rotator scans around the current location until it finds home position. Below you can see a video in action:
The second one runs after every tracking job or on demand through the serial interface and just moves the tracker to the home position. This way, whenever a new traking job begins the user knows that the job starts from zero position.
You can check the code in our repo, and the designs for the hardware too.
It was always our intention to have SatNOGS ground station as unattended as possible in terms of operation. We are now much closer to it!
7 days ago •
The time we've all been waiting for, has come. We are proud to release v2 of SatNOGS Ground Station (Tracking Box) with many upgrades and fixes from the previous version. Notably:
- Redesigned Axis Gear Assemblies. They are now smaller, more robust and reliable based around a much more powerful NEMA 17 Stepper Motor. The two assemblies are now structurally connected, making the whole assembly much more rigid. Also we redesigned the Worm Gear for improved printability on 3D printers.
- Integrated electronics. We designed and built a new PCB to house all electronics (Arduino, and Stepper Drivers) along with an additional PCB as a PSU for voltage regulation and neater cable management. (see previous log)
- Reworked stepper driving code, featuring a much cleaner code, acceleration and deceleration in movement, stop functions and early opto-homing support. (see previous log)
Tripod and On-board computer (TP-Link) stayed the same, with developments on them coming down the road.
A detailed Bill of Materials is available here.
We have also compiled a detailed construction guide, with step by step instructions on how to assemble the Ground Station Tracking box for both Mechanical and Electronics components.
All Designs and 3D printable files can be found here and all PCB files for our electronics shields can be found here.
Development does not stop with v2, and we are already working on the homing/zeroing code that will enable the homing parts we included in v2 to function. Moreover based on more testing we are applying to v2 and feedback from the community, we expect minor fixes to be released soon.
We can't wait to see v2 out there, built by others, so get started and/or provide feedback!