Over on YouTube Mike Ladd (KD2KOG) from the SDRplay technical support team has uploaded a YouTube video showing him running our recently released RTL-SDR Blog L-Band Active Patch antenna on an SDRplay RSP1a. In the video he receives and decodes AERO signals from his car with his RSP1a powering the active patch antenna via the built in bias tee.
If you didn't already hear, we recently released an active (amplified + filtered) high performance patch antenna designed for receiving L-Band satellites such as Inmarsat, Iridium and GPS. The patch is designed to be easily mountable outside on a window, surface, stick, tree branch etc as it comes with easy to use mounting solutions and extension coax, and is enclosed in a fully weather proof plastic cover. If you're interested the product is available over on our store for US$39.95 with free shipping.
You also might want to keep an eye on Mike's YouTube channel, as he notes that in the yet to be released part 2 video he will be giving away the antenna in a competition.
Thank you to Frank for submitting his new RTL-SDR compatible Orbcomm Satellite monitor software called "Orbcomm Receiver". Orbcomm is a low earth orbit satellite communications system that operates in the 137 - 138 MHz frequency range. The satellites specialize in remote IoT and machine to machine (M2M) connectivity, an example use case being a GPS tracker on a shipping container regularly uploading GPS coordinates from anywhere in the world via the Orbcomm satellites. Orbcomm satellite signals are fairly strong and can easily be received with an RTL-SDR and V-Dipole antenna.
We haven't posted about Orbcomm on this blog since 2015 since there is not many interesting things to say about it. The data is all encrypted, and the only information you can really see is Orbcomm satellite ID, frequency and positioning data. Franks software doesn't change this fact, but his software is all open source, so it may be a useful tool for learning about satellite signal DSP processing. Frank writes:
There are a couple different projects out there to decode ORBCOMM signals (Orbcomm-Plotter and MultiPSK). What makes my project different from these is that I wrote it as a learning project. So all of the signal processing, written in Python, is available to the user and is decently documented. I hope this can be a good learning resource for people who want to see a practical example of satellite communications signal processing. Also, my software is open source and free to use.
Currently, the software can do offline or real-time decoding of a single ORBCOMM downlink channel. The transmitted bits of the ORBCOMM signal are demodulated and when the packet type is known, the packet information is decoded. There are a lot of ORBCOMM packets that can't be decoded and of course the message data is encrypted so that information is not available. But, there is still a ton of interesting information available.
The project is still in development so it has some limitations. For real-time recordings, I only support RTLSDRs currently. Also, I'm having trouble getting the real-time processing to work on mac OS, so currently that mode is only supported on linux. However, I have included a couple data files in the repo, so even without an SDR, users can experiment with the signal processing. I welcome any bug reports or suggestions.
SDR Makerspace is a community based in Greece that is run by the European Space Agency and Libre Space Foundation (who are responsible for the SatNOGS project). It provides funding and resources for Software Defined Radio based space communication projects.
Over on YouTube TechMinds has uploaded a video showing how to use the Iridium Toolkit software to receive data and audio from Iridium satellites with an Airspy. Iridium is a global satellite service that provides various services such as global paging, satellite phones, tracking and fleet management services, as well as services for emergency, aircraft, maritime and covert operations too. It consists of multiple low earth orbit satellites where there is at least one visible in the sky at any point in time, at most locations on the Earth.
The frequencies used by the older generation Iridium satellites are in the L-band, and the data is completely unencrypted. That allows anyone with an RTL-SDR or other SDR radio to decode the data with the open source Iridium Toolkit. If you're interested in how Iridium Toolkit was developed, see this previous post about Stefan "Sec" Zehl and Schneider's 2016 talk.
In the video Tech Minds shows decoding of various data, including an audio call and the satellite tracks and heat map of Iridium satellites.
In his setup, Zoltan uses a QRP Labs U3S WSPR transmitter kit that was configured to transmit WSPR at 2m (144 MHz). It is not designed for transmitting the 2.4 GHz QO-100 uplink frequency. To get around that limitation, the moRFeus is used to upconvert the 144 MHz frequency into the QO-100 uplink band by mixing it with a 2,255,634.309 kHz signal. The resulting 2.4 GHz output signal from moRFeus is sent to an amplifier, 2.4 GHz band pass filter, and finally into a 5-turn LHCP helical feed mounted on a 1m parabolic dish.
Successful uplink was confirmed by a UK based WebSDR receiving the QO-100 downlink. Zoltan estimates that the total output power was only 4mW, and actually more like 1-2 mW due to losses in the coax feed.
SDR-Kits.net have begun selling low cost GPS antennas that are modified to receive the Inmarsat satellite frequencies between 1535 MHz to 1550 MHz. They also have a version for Iridium satellites that receives 1610 MHz to 1630 MHz. The antennas are powered by a 3-5V bias tee, so they should work fine with SDRplay, Airspy and RTL-SDR Blog V3 units.
AERO messages are a form of satellite ACARS, and typically contain short messages from aircraft. It is also possible to receive AERO audio calls. STD-C aka FleetNET and SafetyNET is a marine service that broadcasts messages that typically contain text information such as search and rescue (SAR) and coast guard messages as well as news, weather and incident reports. Some private messages are also seen. To decode AERO Mike uses JAERO, and for STD-C he uses the Tekmanoid STD-C decoder.
Mike has also created a very handy bank of frequencies for the SDRUno frequency manager which can be downloaded from here.
We note that if you're interested in waiting, at the end of September we will have an L-band patch antenna set available too. Our antenna will work from 1525 up to 1637 MHz. Prototypes have shown have shown good Inmarsat, Iridium and GPS reception. More details coming next month when manufacturing gets closer to finishing up.
GOES 16/17 and GK-2A are geosynchronous weather satellites that transmit high resolution weather images and data. In particular they are far enough away from the earth to be able to take beautiful 'full disk' images which show the entirety of one side of the Earth. As these satellites are in a geosynchronous orbit, they can be counted on to be in the same position in the sky at all times, so no tracking hardware is required and images can be pulled down constantly throughout the day without having to wait for a polar orbiting satellite to pass over like you would with the NOAA APT or Russian Meteor satellites.
With a low cost WiFi grid dish antenna, LNA and RTL-SDR dongle, any home user within the footprint of one of these weather satellites can receive and decode live images directly from the sky. Setting up a station is overall not too difficult, but it can be a bit fiddly with a number of steps to complete. Below is our comprehensive guide. We'll show how to set up a self contained Raspberry Pi based system with goestools (free), as well as a guide for the Windows PC software XRIT decoder (US$125).
We've attempted to make the tutorial as newbie friendly as possible, but we do need to assume basic RF knowledge (know what antennas, SDRs, coaxial, adapters etc are), basic Linux competency for the goestools tutorial (using the terminal, using nano text editor), and basic Windows competency for the XRIT decoder tutorial (unzipping, editing text files, running programs).
There are two fourth generation NOAA GOES satellites that are currently active, GOES-16 and GOES-17. These transmit HRIT signals, and also transmit shared data from the older third generation GOES 15, and Japanese Himiwari8 satellites. At the moment GOES-16 and GOES-17 are producing full disk images every 30 minutes, and close up "mesoscale" shots of the USA every ~15 minutes. GOES-16 (aka GOES-R) and GOES-17 (aka GOES-S) are also known as GOES-EAST and GOES-WEST respectively. At least one of these satellites can be received from North/South America, Canada, Alaska/Hawaii, New Zealand, Eastern Australia and some pacific islands.
There is also the older generation GOES-15 and GOES-14 which have been placed in standby orbits. These transmit LRIT signals which provide images at a slower rate.
There is also the Korean GK-2A (GEO-KOMPSAT-2A) satellite which is very similar to the GOES satellites. GK-2A covers countries like India, Asia, Australia, New Zealand and parts of Russia. Note that you may have previously heard of the COMS-1 satellite which used to cover this area. Since July 2019 COMS-1 was replaced by GK-2A. Unlike GOES, GK-2A images are encrypted. However it has been found that "sample" encryption keys found online in demo code work just fine.
GK-2A contains both LRIT and HRIT channels, but at the moment only the LRIT channel can be decoded with the currently available software. The LRIT channel sends full disk IR images every 10 minutes in 2200 x 2200 resolution. Compared to the 5424 x 5424 resolution GOES full disk images, this is smaller, but still large enough to be interesting.
Note that even if HRIT decoding is added by the current software, you would require an Airspy or other wideband SDR as the GK-2A HRIT signal bandwidth is 5 MHz. Also since the HRIT bandwidth is so wide, the signal strength is reduced, meaning that you'll need a larger dish. People who have received the HRIT signal note that a 3M+ sized dish seems to be required.
You might ask why bother receiving these satellite images directly, when you can get the exact same images from NOAA at https://www.star.nesdis.noaa.gov/GOES/index.php. Well, you might want to set up your own station to be independent from the internet, or you live in a remote location without internet, or maybe just for the fun and learning of it.
To set up a receiver for GOES 16/17 HRIT or GK-2A LRIT you'll need to purchase a dish antenna such as a cheap 2.4 GHz WiFi antenna, an RTL-SDR, GOES LNA, and a Raspberry Pi if using goestools, otherwise a Windows PC can be used. The total cost could be anywhere from $150 - $200 depending on what pieces you already have available.
Before we start the tutorial, you might want to use an augmented reality Android app like "Satellite-AR" to get a rough idea of where either GOES 16/17 or GK-2A (GEO-KOMPSAT-2A) is in your sky, and if receiving them is even feasible for your location. You'll need to find an area on your land where you can mount a small satellite dish with an unobstructed line of sight view to the satellite (no trees or buildings can be blocking the signal path). If the satellite is low on the horizon (below 25 deg elevation), then things get a little more difficult as you have more obstructions and a weaker signal. But it can still be done, and we're able to routinely get good results at 24.5 deg elevation.
Note that for Europe and Africa, unfortunately there are no satellites that can be received easily with an SDR and LNA. But you might instead be interested in the EUMETCAST service, which can be received from EUTELSAT 10A (Ku band), Eutelsat 5 WEST A (C Band) and SES-6 (C Band) . To receive this service you'll need a DVB-S2 receiver and a satellite dish with appropriate band LNB. You also need a license keys and software which all together cost €100. EUMETCAST reception is not covered in this tutorial, instead see this video.
If you've been following our blog, or have your own RTL-SDR based weather satellite station, then you'll know that the NOAA-15 APT satellite has been experiencing issues lately. There appear to be problems with it's camera scan motor resulting from it running low on lubrication. This is fully understandable as the satellite is 21 years old and well past it's expected life span. The satellite appears to be working some days, and producing garbage image other days.
When NOAA-15 fails for good, don't feel too bad as we still have NOAA-18 and NOAA-19, the Russian Meteor M2, and Meteor M2-2 satellites, and the GOES satellites, all of which can be received by an RTL-SDR. Several new weather satellites are also planned for 2020 and onwards.