# TinyGS vs. SatNOGS: A Comparative Analysis of Open-Source Satellite Ground Station Networks
## 3 SatNOGS
### SatNOGS Ground Station  
There are two types of SatNOGS ground stations, the non-rotator ground station (or fixed ground station) and the rotator ground station (or non-fixed ground station). The first is a simpler fixed GS that requires an omnidirectional antenna (e.g., Turnstile, Lindenblad, or QHF). Consequently, it is unable to receive the weakest and most distant signals coming from the most distant satellites. The second is a more complex and expensive GS, mainly due to the presence of a rotator and a rotator controller. It is able to vary elevation and azimuth angles, allowing for the use of directional antennas and always pointing them in the direction of the satellite during its cross between horizons. In this way, it allows one to receive weaker and more distant signals compared to the non-rotator GS. Figure 2: High-level relationship between SatNOGS parts where the bidirectional arrows represent the sending or receiving of data. Satellites represent supported satellites found in the SatNOGS database [15]. The ground station symbol next to the raspberry symbol represents all the hardware, for example, the antenna, LNA, filter, SDR, rotator, and rotator controller. Starting with the simplest case, if you intend to build the simplest ground station (a fixed ground station) with the minimum number of components, simply construct a GS with:  
* Linux computer (If your Linux computer is a Raspberry Pi, you also will need an SD card)
* Software-defined radio (SDR);
* Antenna. Despite being the simplest and most cost-effective ground station, it is likely to capture few or no signals. Conversely, if you aim to capture more signals within the fixed ground station, it is advisable to add a low-noise amplifier (LNA) and a filter if you are in a location with a strong presence of FM signals. However, as the rotator ground station with LNA normally allows one to receive a larger number of signals, its block diagram will be focused, and it is presented in Figure 3.  
This block diagram is constituted by a Raspberry Pi (models 3 or 4 are recommended [17]), but it could be any Linux computer (It is noteworthy that the Linux computer in question can range from a Raspberry Pi employing the Raspbian distribution to a desktop Linux system utilizing, for instance, the Debian distribution. Although alternative Linux distributions can be employed, it is recommended to adhere to the recommended ones, as outlined in the SatNOGS client Ansible guide [17] for installing the SatNOGS client. Otherwise, you will need to manually install the SatNOGS station software, a procedure explicitly described as a \"tedious and brittle process\" and not recommended [17]. ), where the SatNOGS client will be installed.and is connected to the SatNOGS network, for example, by an Ethernet cable or Wi-Fi. This Raspberry Pi with the SatNOGS client will be responsible for periodically checking the network to see if there are observation jobs to execute. Furthermore, it is connected to the controller, and this is responsible for controlling the motors present in the rotator, in this case, the stepper motors (DC motors are also possible to be implemented), in order to position the antennas in the desired position. If one wants a commercial rotator controller, do not forget to check if it is supported by hamilb-rotctl, otherwise it will not work, since the SatNOGS client uses hamilb. If one wants a homebuilt rotator controller, one can opt for the SatNOGS rotator controller [18]. Figure 3: Block diagram of a SatNOGS rotator ground station with two antennas (VHF and UFH antennas). The rotator is a mechanism composed of stepper motors (or DC motors), which are connected to the antennas and move them by varying their elevation and azimuth angle, thus allowing the antennas to point in the direction of the satellite. The rotator can be obtained commercially or be built at home. If one wants a commercial rotator, one could consider, for example, Yaesu G-5500 and the Alfa Spid XY [17].