The side-bands are below the noise floor in this case, so we have no “false responses” in our cross-correlation. The good thing about the settable attenuation of the Dolph-Chebyshev window is that it can be used to trade-off performance between different features. These properties make this window useful in radar applications.īelow I’m doing the cross-correlation in GNU Radio with a shorter template pulse shaped with a Dolph-Chebyshev window set for 55dB attenuation. For higher attenuations, you have a wider main lobe, while if you want a narrower main love you get less side-band attenuation. There is a parameter that tunes the side-bands attenuation. Indeed, it minimizes the \(L^\infty\) norm of the side-bands. This window has the property that the side-bands have constant attenuation. I use scipy to compute this window, because it is not included in GNU Radio. I have also changed the window for the pulse. However, I think that 6.5ms is a good estimate. However, I don’t know this length precisely, because multipath propagation makes the received pulses a bit longer. Ideally, the template pulse should have the same length as the transmitted pulse. Therefore, it is a better idea to use a shorter template pulse. However, the pulses from the radar are shorter. The keen reader might have noticed that I was doing the cross-correlation with a template pulse that lasted the whole pulse repetition cycle. This produced the strange side-bands below the main reflection. I have found that the signal processing I did there to obtain the cross-correlation was far from optimal. This is a follow up post to my experiments studying OTH radar. In this post I do a detailed analysis of the radar waveform using this recording. It turns out that this signal is a BPSK pulse radar. He did an IQ recording of this signal on the downlink of Meridian 8. We also found a wideband FM signal containing music and announcements in Turkmen, which later turned out to be the audio subcarrier of a SECAM analogue TV channel from Turkmenistan.Ī few days ago, Scott detected a pulsed strong signal through the transponder of the Meridians at a downlink frequency of 994.2 MHz. Unfortunately we haven’t been able to do anything useful with them, maybe because there are several signals overlapping on the same frequency. We have found some OFDM-like signals that seem to be NB-IoT. By measuring Doppler we know that the uplink is somewhere around 700 or 800 MHz. These transponders show all sorts of terrestrial signals that are relayed as unintended traffic through the transponder. After examination with the Allen Telescope Array of these signals, we confirmed that they came from wideband transponders (centre frequency around 995 MHz, 13 MHz width) on some of the Meridian Russian communications satellites (in particular Meridian 4 and 8, but also others). This has led him to discover some signals coming from satellites on a Molniya orbit. His idea is to try to see if this candidate signal can be explained as interference from some satellite. Ever since SETI Insitute published the news of a possible signal received from Proxima Centauri in some of the Parkes telescope recordings at 982 MHz, Scott Tilley VE7TIL has taken up the interest to search and catalogue the satellites that transmit on this band (specially old, forgotten and zombie satellites).
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