RF recording of Vega-C MEO cubesats 436 MHz telemetry beacons

This dataset contains an IQ recording of the 436 MHz telemetry signals of four of the MEO cubesats launched in the Vega-C maiden flight on 2022-07-13: CELESTA, MTCube2, Greencube and AstroBio Cubesat. The recording was done on 2022-07-24 from 40.5958º N, 3.6991º W, 800 m ASL, near Madrid (Spain). This is a urban location, so the RFI is quite high. A 7 element yagi antenna built by Arrow and a USRP B205mini were used. The antenna was held on a tripod and aimed manually. The antenna polarization was horizontal with respect to the local horizon (parallactic angle rotation should be taken into account to derive the sky polarization). It was connected to the SDR with a short (~1 metre) piece of coaxial cable. The signals have rather low SNR, due to the high RFI and the small antenna used. Weak packets from CELESTA and very weak long bursts from Greencube can be seen. Signals from MTCube2 and AstroBio were not detected. The USRP digitized at 4 Msps IQ with a centre frequency of 436.52 MHz. A GNU Radio flowgraph was used for Doppler correction and channelization. A channel of 40 ksps IQ was recorded around the nominal frequency of each satellite. Two different channels were used for AstroBio Cubesat, due to the uncertainty in its transmit frequency caused by a reset of the satellite's radio to factory settings. Each channel is given in a different file, identified by the name of the corresponding satellite. The recordings of the satellites are contained in the files identified as 2022-07-24T18_47_38. The files with later timestamps (2022-07-24T19_25_49 and 2022-07-24T19_29_02) are short recordings of a CW carrier injected into the receiver for absolute amplitude calibration. The data was recorded using GNU Radio metadata format with detached headers and converted to SigMF format in postprocessing. The detached headers of the GNU Radio metadata format are provided with the .hdr extension. The Doppler correction files are also included in this dataset. These are text files that contain tabulated timestamps in seconds of UNIX time and Doppler frequency in Hz. They were generated using the TLEs from Celestrak and the Skyfield Python library. More information about this recording, including the details of the absolute amplitude calibration, can be found in the post "Trying to observe the Vega-C MEO cubesats" by the author.本数据集包含2022年7月13日Vega-C首飞任务发射的4颗中地球轨道（MEO）立方体卫星的同相正交（IQ）采样数据，涉及卫星分别为CELESTA、MTCube2、Greencube与AstroBio Cubesat。本次采样于2022年7月24日在西班牙马德里附近完成，采集坐标为北纬40.5958°、西经3.6991°，海拔高度800米（ASL，高于海平面高度）。该区域为城市环境，因此射频干扰（RFI）水平较高。采集设备采用Arrow公司制作的7单元八木天线与USRP B205mini软件定义无线电（SDR）。天线通过三脚架固定并手动对准目标，其极化方式相对于当地地平线为水平极化（推导天空极化时需考虑视差角旋转的影响）。天线通过一根长度约1米的同轴电缆连接至SDR。由于射频干扰较强且天线尺寸较小，采集到的信号信噪比（SNR）较低。可观测到CELESTA卫星的弱信号数据包，以及Greencube卫星的极弱长脉冲串信号，未检测到MTCube2与AstroBio Cubesat的信号。USRP以4 Msample/s（Msps）的采样率对IQ数据进行数字化，中心频率设置为436.52 MHz。采用GNU Radio流程图实现多普勒校正与信道化处理。针对每颗卫星的标称频率，采集了40 ksamples/s（ksps）带宽的IQ信道数据。由于AstroBio Cubesat的无线电被重置为出厂设置导致发射频率存在不确定性，因此为其采集了两路不同的信道数据。每一路信道数据单独存储为一个文件，文件名以对应卫星的名称标识。卫星的采样数据存储在名为2022-07-24T18_47_38的文件中。带有后续时间戳的文件（2022-07-24T19_25_49与2022-07-24T19_29_02）为注入接收机的连续波（CW）载波的短时长采样数据，用于绝对幅度校准。原始数据采用GNU Radio元数据格式录制，采用分离式头文件结构，并在后期处理中转换为SigMF格式。GNU Radio元数据格式的分离式头文件以.hdr为扩展名提供。本数据集同时包含多普勒校正文件，这类文本文件以秒为单位存储UNIX时间戳与多普勒频率（单位为Hz）的制表数据，其生成基于Celestrak发布的轨道两线元素（TLE）与Python库Skyfield。关于本次采样的更多信息（包括绝对幅度校准的详细步骤），可查阅作者发布的博文"Trying to observe the Vega-C MEO cubesats"。