# TinyGS vs. SatNOGS: A Comparative Analysis of Open-Source Satellite Ground Station Networks
## 3 SatNOGS
### SatNOGS Ground Station
If one wants a homebuilt rotator, one could choose the SatNOGS rotator v3, and there is already a list of the required materials, source files for 3D-printed components(e.g., shaft gear, shaft side, and motor mount), as well as a guide that details how to put all of the components together [17; 19; 20]. Mechanically connected to the rotator are the antennas, which are responsible for receiving the signals from the satellites. As a large number of satellites work in the VHF and UHF bands, a UHF antenna was placed on the block diagram to receive UHF frequencies and a VHF antenna was added for VHF frequencies. There are several types of antennas, and their selection should be based on the signals with which one intends to work. If one is new and does not have much knowledge about antennas, to start with, one can choose one of the commercial antennas present on the SatNOGS wiki [17]. If, despite being new, one wants to build their own antenna, below are two references one might want to look at [20; 21]. Electrically connected to the antennas is the diplexer, and it is responsible for allowing the signals from both antennas to share the same communication channel. If there were no diplexer, it would be necessary to have two communication channels, one for the UHF antenna and another for the VHF. Consequently, the number of components (at least LNA, SDR, and coaxial cables) would be doubled. The filter does not necessarily have to be duplicated because, if it is applied only to block the FM frequencies (88-108 MHz), then it could be placed in the VHF antenna communication channel (30-300 MHz). One can buy a commercial diplexer, but if one wishes to build their own, in order to save some money, one may want to look at the SatNOGS diplexer [22]. Then we have the LNA, which allows us to amplify small signals with minimal noise introduction. It can be powered by a bias tee approach and should be positioned as close as possible to the antenna. If it is not powered by a bias tee, one needs to add its power supply to the block diagram. An example of a recommended and widely used LNA in SatNOGS GS is the LNA4 ALL [17]. Regarding the filter, it aims to block unwanted frequencies, such as blocking the FM band in places where there is a strong presence of FM signals. It is important to take into consideration that if the filter is between the SDR and the LNA, and the LNA is powered by a bias tee, it is necessary to make sure that the current supplied by the bias tee passes through the filter and arrives at the LNA. Then, there is the SDR dongle connected to the computer, a radio communication system consisting of radio components (e.g., amplifiers, filters, and ADC) implemented via software. If one intends to buy an SDR that is not on the list presented on the SatNOGS wiki [17], be careful to ensure that it is supported, since SatNOGS uses the gr-soapy module. Furthermore, it is important to take into consideration that if one uses an LNA powered by a bias tee, one must use an SDR with an activatable bias tee circuit. In terms of recommended and widely used SDRs, there is the RTL-SDR [17]. Finally, one may need to use coaxial cables, which are responsible for transporting the signals between the different components. When using coaxial cables, it is necessary to be careful to verify if one needs connectors and, if so, which types.