# Low-Cost _Ka_-Band Satellite Receiver Data Preprocessing for Tropospheric Propagation Studies  
[PERSON]  
1 atlanTTic Research Center for Telecommunications Technologies, Universidade de Vigo, 36310 Vigo, Spain; [EMAIL_ADDRESS] (F.M. ); [EMAIL_ADDRESS] (F.P.-F.)1  
[PERSON]  
1 atlanTTic Research Center for Telecommunications Technologies, Universidade de Vigo, 36310 Vigo, Spain; [EMAIL_ADDRESS] (F.M. ); [EMAIL_ADDRESS] (F.P.-F.)1  
[PERSON]  
2 Indian Institute of Information Technology Kalyani, Kalyani 741235, West Bengal, India; [EMAIL_ADDRESS]  
[PERSON]  
1 atlanTTic Research Center for Telecommunications Technologies, Universidade de Vigo, 36310 Vigo, Spain; [EMAIL_ADDRESS] (F.M. ); [EMAIL_ADDRESS] (F.P.-F.)1  
Footnote 1: [[https://www.mdpi.com/journal/sensors](https://www.mdpi.com/journal/sensors)]([https://www.mdpi.com/journal/sensors](https://www.mdpi.com/journal/sensors))  
Footnote 2: [[https://www.mdpi.com/journals/pdf/10/1](https://www.mdpi.com/journals/pdf/10/1)]([https://www.mdpi.com/journals/pdf/10/1](https://www.mdpi.com/journals/pdf/10/1))  
introduce variations in the received signal power due to thermally induced changes in the electronics. Our LNB (see Section 2.1.1 and [4]) is subjected to gain variations due to the ambient temperature. Its maximum operational range is \(-40\)\({}^{\circ}\)C to \(+60\)\({}^{\circ}\)C, and the gain changes can be of the order of 5 dB. At our location during summertime (worst case), the maximum temperature range is of the order of 12 \({}^{\circ}\)C with an estimated gain variation of under 2 dB (private communication with the manufacturer). This must be compensated for by subtracting the template. One further problem arises due to the fact that the satellite experiences very small position oscillations of no more than \(\pm 0.1^{\circ}\) (stationkeeping box) [5; 6]. This, combined with the presence of possible small pointing errors--in this experiment, we used fixed pointing--can lead to unwanted signal variations. Again, these must be first minimized by a good pointing and, then, any residual errors induced removed, using the template. However, given as we used a fairly small receive antenna of 65 cm diameter, this is equivalent to approximately a beamwidth of \(1.6^{\circ}\), much wider than the satellite's stationkeeping box. This means that pointing errors will be a second-order factor in comparison with the temperature-induced LNB gain changes. We were interested in characterizing rain attenuation statistics. However, in addition to rain, the received beacon signal power level can also be affected by other phenomena: gases, clouds, scintillation [7], temperature fluctuations of the unit electronics, antenna strut thermal expansion [8], the accuracy of the satellite tracking [5], etc. The raw received beacon signal in dBm can be calculated as [5; 9; 10]:  
\[P_{r}=EIRP-L_{fs}+G_{ra}+G_{rx}-A_{g}-A_{c}-A_{r}-A_{s}, \tag{1}\]  
where _EIRP_ is the satellite's Equivalent Isotropically Radiated Power (dBm), \(L_{fs}\) is the free space loss (dB), \(G_{ra}\) is the receiving antenna gain (dBi), and \(G_{rx}\) is the receiver gain (dB). The last four terms in (1) correspond to different propagation effects and are expressed in dB: \(A_{g}\) includes water vapor and oxygen loss; \(A_{c}\) corresponds to cloud loss; \(A_{r}\) is the rain-induced attenuation; \(A_{s}\) embodies the scintillation. (Sometimes, the scintillation is represented as a gain, and thus, the sign in the above equation is changed to \(+\).) The total tropospheric attenuation \(A\) (dB) is the sum of these four terms [5; 9; 10]:  
\[A=A_{g}+A_{c}+A_{r}+A_{s}. \tag{2}\]  
As said, we were interested in measuring rain attenuation, \(A_{r}\). One first option to remove the impact of gases and clouds is by measuring them directly using a radiometer, as in [11; 12; 13]. This is a sophisticated piece of hardware, even more expensive than a beacon receiver, and was not available to us. Radiometer data could be replaced by alternative data sources.