We are getting more familiar with the received data and start to realize the amount of work ahead of us. Not only will it be very difficult to decide on the bands that shall be investigated each week, it is even more difficult to identify various signals that we receive and how to interpret them.
Planning of Measurements
The experiment is set up such that each week before Thursday we send a list of parameters for the recordings to BioTESC. This parameter list contains the SDR input that we want to use (LOW, WIDE, HIGH), the frequency range (in VHF, UHF, L, S band), the gains of the LimeSDR, the sample rate, bandwidth resolution etc.. We cannot investigate all frequency bands at the same time and the bandwidth that we can record at a time is limited to a view MHz. So when should we record which band??
There is always something interesting to record in each of the bands. Shortly after installation we were informed by ARISS about various activities that they plan (you can stay up-to-date using this calendar: https://www.amsat-on.be/ariss-calendar-with-scheduled-contacts-by-the-ariss-operation-team/) in VHF and UHF. Additionally, we have various satellites that pass the ISS regularly and we have ground stations that can send transmissions while pointing to the ISS to test our experiment’s sensitivity. Long-time focus on each of the bands shall also be performed without interruptions. Once the first results of MarconISSta have become more public, other users are expected to send requests for frequency investigations. We underestimated the need for a useful planning tool and are currently in the quick development of such a tool. In the meantime, the planning is done manually. Let us know if there is something that you want to be investigated by leaving a comment!
After the first few days, many interesting recordings have been made. The main goal of MarconISSta is to develop heat maps of the global use of spectrum. One challenge that we identified early in the development of the visualization tools is how to handle recordings that result from the system itself and recordings that are special for the ISS. The system has some internal “noise” in the form of DC offset, oscillator artefacts etc. that are constantly seen in the recordings. Obviously, these have to be neglected for the global heatmap. Additionally, there are transmissions that are only sent when the ISS is passing over a certain region. With having ESA astronaut Alexander Gerst on the ISS, there are more European school contacts than usual. Should these school contacts be added to the global heatmap or not? Additionally, the high power responses of the radio operators aboard the ISS should not be included in the global heatmap. Due to these reasons we might need some time to publish the first scientifically relevant heatmaps.
The most fun part in the early days of operations is to look at various transmissions to find out what they are. Some examples are given below. You can see two “waterfall” diagrams for some of the recordings. The recordings have been preprocessed to show a flat “layer” when there is nothing received. The DC offset at the center frequency and some constant disturbances slightly influence this “layer”. But the more interesting observations are the signals that “pop up” and dissappear again. Can you find out what they are? This includes look at the signal itself (strength, bandwidth, time resolution, …) and at the orbital position that the ISS had when the signal appeared. Find some examples below, we will publish the origin of these recordings in a few days. Use GPredict (http://gpredict.oz9aec.net/) or Heavens Above (https://www.heavens-above.com/) to find out where the ISS has been at the time of recordings.