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!
Some observations
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.
You may expect many ghost signals on Lime without dedicated Band Pass Filters… That is my experience from terestrial use. Counting your unit is in low orbit, you can assume that your situation is almost like on ground, with open fresnel zone like cone shaped to earth. Good luck with all that 🙂
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Yes, thank you Djani, it is exactly like you are saying! We experience quite a lot of “ghost signals”, harmonic artefacts etc. And it is exactly what we want to see – many current small satellites do not have good filtering, so it is great to see what they receive. A future update to the experiment would include band pass filters to focus on what “really” is in the band. 73s
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That is much better. In case you may need calibration signal source from East Adriatic island, please let me know. 73
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Great! We’ll have a little competition “All power to the ISS” in a few weeks, where we ask terrestrial stations to send some signals to the ISS. We’ll announce this here, but also I took a note from your offer. Which bands could you offer (VHF/UHF/L/S)? 73
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I am able to do up to 15 GHz but low power only.
We just need to agree what antenna and gain you need => ERP
Can measure and provide GPS referenced source over Agilent e7495b and ERASynth+ signal generator plus some HAM, Marine and Air Band transceivers…. 73
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Djani, sorry for the late reply! We now have a scheduler for our operations: https://marconissta.com/scheduling/
First tests with our own ground statino shows reception with about 50W RF power and an antenna gain of approx. 16 dBi. If you do any testing, let us know when and where and we’ll try to identify your transmitter!
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Hello Martin,
Thank you for information.
In that case, must pick up from my main site (in Zagreb)
PA for 144 MHz 30W
PA for 432 MHz 50W
To be used with Lime SDR or ERASynth
And some antennas.
At the moment can do only 5 W from FT817 on 144/432 on dual band magnet antenna
in corner reflector so gain 8-10 dBi max
73
Djani
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I think you could do some tests with the equipment that you have, too. Depending on the losses on the ARISS cables and our own equipment, we might still see a signal. Just make sure not to send on the center frequency of the band that we investigate and let us know when and on which frequency you transmitted! 73s
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Deal…
Please let me know which input you are using LNAW or LNAL? With or without modification?
73
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Just see one window of opportunity for tomorrow from 2018-09-19 21:20:00+0200 to 2018-09-19 21:35:00+0200 My signal is going to be on 435.430,00 CW 9A4DB keyed by hand.
Please let me know is that OK for you?
73
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Sounds good! We are using LNAL of Ch. 0 with the modification.
Our software currently only stores one measurement each 3 seconds, so we won’t be able to see the signal on the carrier. Basically just sending the carrier would be best. Please do not use any form of Doppler correction, I would like to test whether we can locate your position based on the Doppler.
Thanks & 73
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LNAL with mod must be OK.
So no Doppler correction, just carrier, rough 10 sec ON, 10 sec OFF, please expect signal freq with no calibration i(t is common FT 817 5W – no external ref. clock source). Looking forward to results 73
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Great. I look forward to see if we can hear you. We should have the results on Thursday/ Friday.
FYI: Not sure if you are aware of the RF coupler that we have on the ISS, it will decrease the received signal by additional 20-25 dB. But still let’s see what we can get!
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Thumb up 🙂
Yes I know… have seen the setup block schematic.
Just checked, at Maximum altitude tomorrow, 21:28:04 47° 141° (SE) we have 547 km optical distance predicted… that may be enough.
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Transmit went on from 21:25:00 each 10 sec carrier on/off, last transmission ended on 21:32:10 freq was 435.430,00 CW/USB
Visual was not possible because of moon and light clouds. Waiting for report.
Thumb up.
73
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Thank you! We will receive the measurements tomorrow and will look into them over the weekend. 73
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Looking forward to that, tnx….
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Sorry for letting you wait so long. Sadly, we could not identify your signal in the measurements. I suppose you sent around 21:25 MEST, not UTC? A big problem was that the area of interest is overlayed with a strong wideband signal. I will upload a figure of that during the weekend. At the same time, your signal just might have been to weak. Another groundstation sent a signal with ~50-75W and 18dBi antenna gain, it was just seen 10dB above the noise. But let’s keep working and see what can be achieved with your other equipment! 73s Martin
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Thank you Martin.
Yes, my timing is in CET
21:25:00 each 10 sec carrier on/off, last transmission ended on 21:32:10
or
GMT 19:25:00 each 10 sec carrier on/off, last transmission ended on 19:32:10
Freq was 435.430,00 CW/USB 5W in 6-7 dBi antenna,
main lobe to 47deg elevation and 141deg heading.
Usually ISS can be reached with fair results on FM using 5 W and 3-4 element yagi
but in case that some wideband noise/signal is around,
than may be to optimistic to spot mine 😀
On my location & ground level, that freq is clear, but must check with limeSDR –
because some ghost images from GSM and TETRA services, may be present too.
73
Djani
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BTW Some of my (optimistic) math on 547 km @ 435 MHz
Effective Isotropic Radiated Power Level of: 43.99 dBm
Free Space Path Loss: 140.0 dB
Expected sensitivity on your side -98 dBm (20 dB loss of cables + coupler, included)
My local measurements on the same LNAL modified LimeSDR RX are:
-60 dBm source signal & – 50 dB att & – 6 dB signal spliter
& still plenty of available/detectable signal)
Therefore only in case of clear freq we may have some chances to detect….
73
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I can confirm your observations, in the lab we also were able to receive signals with about -110dBm. But for me it is early to draw conclusions. We still play with the gains to get better signals. The loss on the ARISS cables is not really assessed, additionally the antenna points nadir, accordingly the gain decreases for higher passes.
Regarding your link calculations:
44 dBm e.i.r.p.
140 dB free space loss
20 dB coupler loss (conservative)
—
-116 dBm which would be just a little too weak. But let’s keep trying!
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Right.
Here some pictures and explanations =>
https://discourse.myriadrf.org/t/ground-control-to-major-tom/3371/2
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