Recently Jared Boone, creator of the HackRF portapack posted on his blog about his experience with trying to receive Iridium satellite signals. The HackRF is 8-bit, ~0 – 6 GHz, RX/TX capable SDR, and the Portapack is a kit that allows the HackRF to go portable, by adding an LCD screen, battery pack and control wheel. Iridium is an L-band satellite service that provides products such as satellite phones and pagers. Back in December 2014 we posted how it was found that Iridium pager messages could be decoded.
To receive Iridium Jared used a simple ceramic patch antenna mounted on a piece of cheap copper clad fibreglass. This simple antenna was good enough to receive the Iridium signals with good strength. With this set up Jared was able to easily go outside and receive some packets and record them. He writes his next steps are to try and run the Iridium pager decoder on them and see what packets he captured.
To show that a specialized antenna is not required to receive L-band Inmarsat AERO satellite signals, YouTube user SkyWatcher has uploaded a video showing how he was able to receive these signals with a cheap DVB-T antenna. SkyWatcher writes:
I’ve recently upgraded from my RTL-SDR sticks (E4000, R820T2) to an Airspy Mini.
I did some testing during the last week and found it very interesting that I was able to receive Inmarsat L-Band signals indoors, with just a DVB-T antenna and amplifier behind the window, no downconverter, no special antenna, no super low-noise amplifier. The window is facing south, with a few degrees to the east and the satellite I’ve received was Inmarsat 15.43W. So, angle antenna to satellite should be estimated 20 degrees.
I’ve used a 18dB DVB-T/Satellite-TV inline amplifier as a ‘LNA’ (noise < 5dB) and a VHF/UHF DVB-T antenna which seems to be a stacked dipole, and therefore should be quite wideband and should make a reasonable general purpose antenna. Anyway, I did not expect it to work on 1.5GHZ at all. Also, I want to mention that the inline amplifier is rated 5 to 18V, but it works just fine with the 4.5V from the Airspy Mini.
It seems that with 10dB S/N, Aero reception is possible and with about 12dB S/N, it is getting reliable.
In general, I am very satisfied with the upgrade to the Airspy Mini. It has a much lower noisfloor and a much cleaner spectrum, compared to my old RTL SDRs. Also, I am very happy with the CPU-usage which is only about 12% on my i5-3210M when using 2.4MHz bandwith, and 18-20% with a bandwith of 4.8MHz.
Together with the ability to use SpectrumSpy and the very useful decimation-feature, the Airspy Mini is the best option to upgrade from a RTL-SDR for me at the moment. Anyway, of course this is just my very personal opinion…
AERO is essentially the satellite based version of ACARS, and the L-band signals contains short ground to air messages with things like weather reports and flight plans intended to be transmitted to aircraft. To decode it with an SDR, the JAERO software can be used.
A satellite tracker is a motorized unit that points a directional antenna towards passing satellites. Most satellites are not in a fixed orbit, and will fly over your head a few times a day and will be receivable for a few minutes, and a directional antenna is usually recommended since the signals can be weak. The goal of the SatNOGS project is to set up various volunteer satellite tracker stations around the world, and network the received data on the internet, so that satellite data is always being received and shared.
Although the tracker works, he admits that there are some problems and that it is probably not as good as the SatNOGS recommended build, which is a more permanent solution. But the SatNOGS build requires access to a 3D printer and higher quality components, so Paul’s solution is a much cheaper solution to implement at least for experimentation.
It is well known that the NOAA satellites broadcast weather satellite images which can be received and displayed with an RTL-SDR and computer. What is less known is that there is a telemetry beacon that is also transmitted by the same satellites. The telemetry not only contains data such as the current spacecraft time, day and ID, but also contains scientific data from on board instruments such as:
The HIRS/3 and HIRS/4 instruments which is a high resolution infrared sounder which can be used to create a low resolution multi-spectral scan of the earth. (more info)
The Space Environment Monitor (SEM-2) which has a Medium Energy Proton and Electron Detector (MEPED), and a Total Energy Detector (TED). This experiment is used to measure the effect of the sun on satellite communications. (more info)
The experimental DCS/2 transmitter which retransmits signals from 401.65 MHz sea buoys, arctic fox collars, sea ice monitors, weather balloons and more. (more info pdf)
The ARGOS Advanced Data Collection System (ADCS) which amongst other uses is used in research for tracking animal GPS collars around the world.
His results show that the dish outperforms the helix antennas by a significant amount, but only once he took it outdoors. The 10-turn helix antenna also worked better than the tin can helix, although he found that it required very accurate pointing.
Inmarsat are geostaionary satellites that transmit signals on L-band at around 1.5 GHz. They transmit signals that can be decoded with an RTL-SDR, such as STD-C EGC (weather, messaging and safety messages for boats), as well as AERO (the satellite version of ACARS for aircraft).
Outernet are a startup company that hope to revolutionize the way people in regions with no, poor or censored internet connectivity receive information. Their service is downlink only, and runs on C and L-band satellite signals, beaming up to date news as well as other information like books, educational videos and files daily. To receive it you will need one of their official or homemade versions of the Lighthouse or Lantern receivers (the latter of which is still to be released), or an RTL-SDR or similar SDR. Recently they began test broadcasts of their new 5 kHz 1539.8725 MHz L-band signal on Inmarsat I4F3 located at 98W (covers the Americas), and they hope to begin broadcasts in more regions soon too.
The typical RTL-SDR is known to often have poor or failing performance above 1.5 GHz (though this can be fixed to some extent), so Outernet have been working on an L-band downconverter. A downconverter works by receiving signals, and shifting them down to a lower frequency. This is advantageous because the RTL-SDR is more sensitive and does not fail at lower frequencies, and if used close to the antenna, the lower frequency allows longer runs of cheap coax cable to be used without significant signal loss.
Earlier this week we received in the mail a prototype of their downconverter. The downconverter uses a 1.750 GHz LO signal, so any signal input into it will be subtracted from this frequency. For example the STD-C frequency of 1.541450 GHz will be reduced to 1750 MHz – 1541.450 MHz = 208.55 MHz. This also means that the spectrum will appear reversed, but this can be corrected by selecting “Swap I & Q” in SDR#. The downconverter also amplifies the signal with an LNA, and has a filter to remove interfering out of band signals.
The prototype Outernet downconverter circuit board.Specsheet for the downconverter.
We tested the downconverter using their patch antenna which they had sent to us at an earlier date (the patch antenna is used and shown in this Inmarsat STD-C reception tutorial). Our testing found that overall the downconverter works extremely well, giving us much better signal levels. Previously, we had used the patch + LNA4ALL and were able to get reception good enough to decode STD-C and AERO signals, but with the requirement that the patch be carefully pointed at the satellite for maximum signal. With the downconverter the signals come in much stronger, and accurate pointing of the patch is no longer required to get a signal strong enough to decode STD-C or AERO.
The downconverter can be powered by a bias tee connection, and this works well with our bias tee enabled RTL-SDR dongles. We also tested with the bias tee on the Airspy R2 and Mini and had no problems. It can also be powered with a direct 5V connection to a header, and they note that the header will be replaced by a USB connector in the production version.
The release date and exact price that these will be sold at is not confirmed, but we believe that it will be priced similarly to upconverters at around $50 USD or less. A good low cost downconverter should help RTL-SDR and other SDR users receive not only the Outernet signal better, but also other satellite signals such as STD-C and AERO. Although the input is filtered and the RF frequency is specified at 1525 to 1559 MHz, we had no trouble receiving signals up to GPS frequencies of 1575 MHz, and even up to Iridium signals at 1.626 GHz, though reception was much weaker up that high.
Below are some screenshots of reception. Here we used the Outernet patch antenna sitting in a windowsill with the downconverter directly after the antenna, and then 10 meters of RG6 coax cable to the PC and bias tee enabled RTL-SDR. We found that with the downconverted ~200 MHz signal the loss in the RG6 coax was negligible. Better reception could be obtained by putting the patch outdoors. In some screenshots we used Vasilli’s R820T driver with the decimation feature, which allows you to zoom into narrowband signals much more clearly.
Some AERO Signals Zoomed in with the Decimation feature in SDR#. Received with the Outernet downconverter and patch antenna.Some AERO and other Signals Zoomed in with the Decimation feature in SDR#. Received with the Outernet downconverter and patch antenna.Signals zoomed out. Received with the Outernet downconverter and patch antenna.
The GOMX-3 is a CubeSat which carries an experimental ADS-B repeater. Since it is a satellite the experimental receiver hopes to be able to receive ADS-B from orbit, then beam it back down to earth at a frequency of about 437 MHz using a GFSK at 19200 baud high data rate transmission protocol. From space the GOM3-X satellite can see many aircraft at one time and space based tracking allows for aircraft tracking over oceans.
Recently the creators of the satellite, GomSpace released a complete decoder for the ADS-B downlink, and now it has also been turned into a GNU Radio flowgraph by Daniel Estevez which can output decoded aircraft position data directly to a KML file which can then be opened in Google Earth or similar. This blog by DK3WN shows several logged decodes of the satellite and shows what the signal looks like in SDR#. Some of his posts also curiously shows what looks to be a Windows decoder, or logger, though we were unable to find a download for it.
Decoding the downlink should give you real time ADS-B data in your area, but the full log of stored stored data is apparently only downloaded when the satellite passes over the GomSpace groundstations which are mostly located in the EU.
[Also mentioned on Hackaday]
The GOMX-3 ADS-B Downlink Signal.Logged aircraft detected by the GOM3-X Satellite ADS-B Receiver. Major flight corridors are visible.
Over on his YouTube channel Adam 9A4QV has uploaded a video showing a commercial Inmarsat front end which he reverse engineered to use with his RTL-SDR. The front end is a duplexor, which allows both receive and transmit to occur on the same channel, but to use with the RTL-SDR Adam only uses the receive part. Inside the front end is a large cavity filter, ceramic filter, and about 60 dB of total L-band gain from MMIC amplifiers.
In the second video Adam hooks up the Inmarsat front end to his RTL-SDR and home made patch antenna. The results show that the signals are very strong when using the commercial front end. In a previous post we showed Adam’s results with two LNA4ALL amplifiers. The commercial front end seems to give much stronger signals, but the results with one or two LNA4ALL are adequate enough for decoding.
Over the last few weeks Adam 9A4QV has been testing L-Band Inmarsat reception with his LNA4ALL low noise amplifiers. In a previous post he tested reception with two LNA4ALL and found that he got an improved SNR ratio over using just one LNA4ALL. In his latest video he tests Inmarsat reception with three LNA4ALL’s and two L-band filters. His results show that the SNR is improved over using two LNA4ALL’s, and can almost match the results obtained by a commercial L-band front end which he also demonstrated in a previous video.
Mario Filippi, a regular contributor to our blog and to the SDR community recently wrote in with an article showing how he built an S-Band (2 – 4 GHz) antenna for use with the HackRF. Of course the antenna can be used with any other SDR that can receive in this range, or with an RTL-SDR and downconverter. We post his article below.
S -Band Antenna for use with the HackRF One Author: Mario Filippi, N2HUN
Ever since purchasing a HackRF One, which receives from 1 MHz – 6.0 GHz I’ve always wanted to explore the world above 1 Gig, specifically the 2.0 – 2.7 GHz portion of the S-band. This portion of the band is populated with satellite communications, ISM, amateur radio, and wireless networks. A good, homebrew antenna for S-band was needed, so with parts mostly from the junk box, a 2250 MHz S-band right hand circularly polarized omni-directional antenna was built. Below is a step by step tutorial on building this antenna. Plans were from UHF-Satcom’s site.
The final S-band antenna
Step 1: Take a 12” x 12” galvanized plate a mark with diagonal lines to find the center.
Mark the center of the plate
Step 2: Using a scribe, trace a 130 mm diameter circular pattern onto the plate.
Trace a 130mm circle from the center
Step 3:Cut out the circle with tin snips.
Cut our the circleThe resulting 130mm circle
Step 4: For the coil, solid copper antenna wire is used and turned around a 31 mm diameter pill bottle, resulting in a coil approximately 40 mm diameter.
Wind copper wire to create a coilThe resulting roughly shaped coil
Step 5: To space the turns 27 mm apart two heavy plastic drinking straws are marked at 27 mm intervals.
Mark two straws at 27mm intervals
Step 6:Drill holes at each 27 mm mark.
Drill holes into the 27mm marks
Step 7: Thread the coil through the two straws and allow it to sit for a few days to get into shape.
Thread the copper wire through the straws
Step 8: A 2mm thick Plexiglass™ piece was marked so each straw would be 40 mm apart, then the bottoms of each straw were set in place with gobs of hot glue. Coil turns were hot glued at straw holes.
Straws spaced 40mm and glued onto plexiglass
Step 9: Plexiglass™ piece and straws were hot glued to the 130 mm ground plane and a hole was drilled for an F connector later on. Coil was soldered at bottom to center pin of F connector.
Glue the plexiglass onto the 130mm ground plane
Step 10: Add a coat of paint to make it look a lot better! Attach the antenna to a gooseneck suction cup mount with Velcro®. Mount on an outside window, and it is now ready for action! RG/6 coax was used.
S-Band antenna paintedS-band antenna mounted
Note that the dimensions of the coil were approximate to the dimensions specified in the UHF-Satcom plans. Since this antenna was for receive only, I did not sweat the measurement details. Hot glue was used since this was a prototype to be used only on occasion and not when the weather was inclement. The omni-directional design was chosen instead of the LHCP/satellite dish combo (both plans are outlined in the UHF-Satcom site) because I wanted to receive signals from all directions. And since the HackRF One has a built-in preamplifier, an outboard in-line filter was not used.
This may not be the best or only way to construct an S-band antenna; surely other more mechanically/electronically gifted individuals will do a much better job. Initial testing shows that the little antenna, when adjusted in different directions, is picking up actual signals in this portion of the band. You can test that by looking at a signal on the waterfall, then disconnecting the antenna; if the signal remains then you may have a spurious signal from the receiver. I hope this article encourages others to look above 1 Gig mark on the spectrum. You don’t need a HackRF One necessarily as most SDR dongles cover up to at least 1.6 GHz. With a dongle you can explore other bands such as the L-band ( 1 – 2 GHz) using the right antenna and preamp; check previous articles in this website (www.rtl-sdr.com) for details. A hearty thanks to the folks at UHF-Satcom for their S-band antenna plans and information.
Outernet is a new satellite service that aims to be a free “library in the sky”. They continuously broadcast services such as news, weather, videos and other files from satellites. Their aim is to provide up to date information to users in locations with little to no internet (rural, third world and sea), or in countries with censored internet. It may also be of interest to disaster preppers. Currently they have an active Ku (12 – 18 GHz, though due to be discontinued shortly) and C-band (4 – 8 GHz) satellite service, and now recently have their L-band (1.5 GHz) service active. The L-band signal is currently broadcasting at 1539.8725 MHz over the Americas, 1545.525 MHz over Europe/Africa/India and 1545.9525 MHz over Asia/Pacific.
To receive their L-Band service you will need an RTL-SDR capable of receiving 1.5 GHz, like a R820T/2 RTL-SDR (preferably at least passively cooled like our RTL-SDR Blog models as some R820T/2 units tend to fail at 1.5 GHz without cooling) or an E4000 dongle. You will also need an appropriate L-Band antenna and L-Band amplifier.
To help with these hardware requirements, Outernet have just released for sale an E4000 RTL-SDR with bias tee enabled ($39), an L-band satellite patch antenna ($24) and an L-Band LNA ($19). There is also a E4000 + LNA bundle ($49) available. The E4000 comes in a metal case, and has the bias tee always on. The LNA requires bias tee power and is also compatible with our RTL-SDR Blog units that have the bias tee. The patch antenna is tuned for 1525 – 1559 MHz and is the production version of the prototype antenna we used in our Inmarsat STD-C tutorial. Combined with an LNA we found that the patch antenna gives good performance and can also be used to receive other services such as Inmarsat STD-C and AERO. Currently shipping is only available within the USA, but they write that they will have international shipping available shortly.
The L-Band Outernet signal decoders aren’t finalized yet, but we expect them to be released in a matter of days to weeks. They will have decoders available for the $9 CHIP computer and Raspberry Pi 3 platforms. They way it works is that you plug your RTL-SDR with L-band LNA and patch antenna connected into the CHIP or Raspberry Pi 3 which is running their customized image. The CHIP/Pi3 then broadcasts a WiFi access point which you can then connect to with any device, and access the files as they are downloaded. Once these decoders are released we’ll do a full tutorial on receiving the Outernet L-Band service with an RTL-SDR.
The Outernet L-Band Patch AntennaThe Outernet L-Band LNAThe Outernet E4000 RTL-SDR in metal case with bias tee.
Recently we posted new that Outernet had released their 1.5 GHz LNA, Patch Antenna and E4000 Elonics RTL-SDR + E4000/LNA Bundle. When used together, the products can be used to receive the Outernet L-band satellite signal, as well as other decodable L-band satellite signals like AERO and Inmarsat STD-C EGC. Outernet is a new satellite service that aims to be a free “library in the sky”. They continuously broadcast services such as news, weather, videos and other files from satellites.
A few days ago we received the LNA and patch antenna for review. The patch antenna is similar to the one we received a while ago when writing our STD-C EGC tutorial, although this one is now slightly larger. It is roughly 12 x 12 cm in size, 100g heavy and comes with about 13 cm of high quality RG316 coax cable with a right angled SMA male connector on the end. The coax cable is clamped on the back for effective strain relief.
The Outernet patch antenna and LNA
The LNA is manufactured by NooElec for Outernet. It amplifies with 34 dB gain from 1525 – 1559 MHz, with its center frequency at 1542 MHz. It must be powered via a 3 – 5.5V bias tee and draws 25 mA. The package consists of a 5 x 2.5 cm PCB board with one female and one male SMA connector. The components are protected by a shielding can. Inside the shielding can we see a MAX12000 LNA chip along with a TA1405A SAW filter. The MAX12000 (datasheet here) is an LNA designed for GPS applications and has a NF of 1 dB. It has a design where there are two amplifiers embedded within the chip, and it allows you to connect a SAW filter in between them. The TA1405A SAW filter appears to be produced by Golledge (datasheet here), and it has about a 3 dB insertion loss.
The Outernet L-Band LNAInside the Outernet LNA
We tested the patch and LNA together with one of our V3 RTL-SDR Blog dongles, with the bias tee turned on. The LNA was connected directly to the dongle, with no coax in between. The patch antenna was angled to point towards the Inmarsat satellite. A 5 meter USB extension cord was then used to interface with a PC. The images below demonstrate the performance we were able to get.
Outernet Signal
Outernet Signal with 4x Decimation
AERO
STD-C EGC
The Outernet team writes that a SNR level of only 2 dB is needed for decoding to work on their signal. With the patch and LNA we were able to get at least 12 dB so this is more than good enough. Other signals such as AERO and STD-C EGC also came in very strongly. Even when not angled at the satellite and placed flat on a table it was able to receive the signal with about 5 dB’s of SNR.
In conclusion the patch and LNA worked very well at receiving the Outernet signal as well as AERO and STD-C EGC. We think these products are great value for money if you are interested in these L-Band signals, and they make it very easy to receive. The only minor problem with the patch antenna is that there is no stand for it, which makes it difficult to mount in a way that faces the satellite. However this issue can easily be fixed with some sellotape and your own mount.
In the future once the Outernet Rpi3 OS and decoder image is released we hope to show a demonstration and tutorial on receiving Outernet data.
The Geostationary Operational Environmental Satellite (GOES) is a weather satellite placed in geosynchronous orbit (same position in the sky all the time) which is used for weather forecasting, severe storm tracking and meteorology research. It transmits full disk images of the earth on its Low Rate Information Transmission (LRIT) signal, and weather data images and text on its Emergency Managers Weather Information Network (EMWIN) signal. EMWIN is a service for emergency managers that provides weather forecasts, warnings, graphics and other information in real time.
In his post devnulling writes about receiving GOES:
GOES LRIT runs at 1691.0 MHz , EMWIN is at 1692.7 MHz and is broadcasted from GOES-13 and GOES-15. GOES-14 is currently in a backup position to take over in either fails.
For the hardware side, it is recommended to use roughly a 1.2m or larger dish, depending upon how far north you are, you may need a 1.8m dish (larger the better). Repurposed FTA or C-band dishes are easy to come by and work well.
I made a 5 turn helical feed with some 12ga copper wire and a piece of copper plate, and used this calculator to design it – https://jcoppens.com/ant/helix/calc.en.php
I have a short run of coax into the LNA/Filter box. The first LNA is a TriQuint TQP3M9037 which has a very low noise figure (0.3 dB NF and 22 dB gain at 1.7 GHz).
That is ran into a Lorch 1675 MHz filter (150 MHz pass band), then a LNA4ALL and another Lorch before going over a 30ft run of RG-6 to the SDR.
I am using @usa_satcom (twitter.com/usa_satcom, usa-satcom.com)’s LRIT Decoder and that feeds into XRIT2PIC to produce the images and other data streams. By default the decoder only works with the Airspy, but with a custom GNU Radio UDP block, it can be fed with other SDRs like the BladeRF/USRP/SDR Play. A regular R820T(2) RTL probably won’t work because of the higher frequency (rtls tend to not work above 1.5 GHz) and 8 bit ADC. I’m going to try and use the Outernet e4k to see if I can pickup the EMWIN signal in the near future.
EMWIN is broadcasted on 1692.7 MHz, along with being encoded in the LRIT stream at 1691 MHz. The 1692.7 MHz signal is stronger and narrower, so it is easier to pickup. For decoding EMWIN I used @usa_satcom’s EMWIN decoder that piped data into WxEmwin/MessageClient/Weather Message Server from http://weathermessage.com.
LRIT will contain the full disk images from GOES-15, and relayed images from GOES-13 and Himawari-8. It will also included zoomed in pictures of the USA, and northern/southern hemispheres. The images will be visible light, water vapor and infrared. The full disk images are transmitted every 3 hours, with the other images more often. EMWIN will contain other weather data, text, charts, and reports.
It seems as though it may be possible to receive LRIT and EMWIN signals with an RTL-SDR since the signals are at 1690 MHz, which should be covered by cooled R820T2 and E4000 dongles. The only hardware requirements would be a 1m+ dish, 1690 MHz L-band feed, and an LNA + filter.
In 2017 these satellites are due to be replaced by new ones that will use a HRIT signal, which will be about 1 MHz. New software to decode this signal will be required then, but we assume the same hardware could still be used as the frequency is not due to change significantly.
Please note that the decoding software is only available by directly contacting usa-satcom, and devnulling writes that you must have the proper equipment and be able to show that you can receive the signal first before attempting to contact him.
GOES Full Disk ImageOne of several received EMWIN images
A few days ago we posted a review on the Outernet LNA which can can be used to help receive their new L-band service signal. Their LNA uses a filter which restricts the frequency range from 1525 – 1559 MHz as this is the range in which the Outernet signals are located.
Additional Note Regarding the Downconverter: Also, it appears that the Outernet downconverter prototype that we posted about back in May has unfortunately been discontinued indefinitely and will not enter mass production. For now the LNA is the best option for receiving their signal.
At this year’s hacker themed Eleventh Hope conference, Stefan “Sec” Zehl and Schneider gave a talk which discusses their latest work on decoding data from Iridium satellites using SDR’s. Iridium is a truly global satellite service which 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. There are currently 72 operational satellites operating.
In their talk they discuss how Iridium security is moderate to relaxed, pointing out that Iridium claims that the majority of ‘security’ comes from the complexity of the system, rather than actual security implementations. They then go on to discuss how the Iridium system works, how to receive it with an RTL-SDR or HackRF/Rad1o, how the gr-iridium decoder implementation works, and how to use it to actually decode the data. Later in the presentation they show some interesting examples such as an intercepted Iridium satellite phone call to a C-37 aircraft.
Outernet is a relatively new satellite service which aims to be a “library in the sky”. Essentially their service is going to be constantly transmitting files and data like news and weather updates from geostationary satellites that cover almost the entire world. Geostationary means that the satellites are in a fixed position in the sky, and do not move over time. By simply pointing a small patch antenna at the sky (with LNA and RTL-SDR receiver), it is possible to download and decode this data from almost anywhere in the world. Their aim is to provide up to date information to users in locations with little to no internet (rural, third world and sea), or in countries with censored internet. It may also be of interest to disaster preppers who want an “off-grid” source of news and weather updates. It can kind of be thought as a kind of one-way download-only internet service.
Currently the L-band service is being tested, and while they are not yet sending actual Outernet files, they are already sending several daily test files like small videos, images and text documents as well as GRIB files for mariners. At a maximum you can expect to receive up to about 20 MB of data a day from their satellite. Previously they had C-band services but these required large satellite dishes. The C-band service is due to be discontinued at some point in the future.
In this guide we’ll show you how to set up an Outernet L-band receiver with an RTL-SDR dongle. If you enjoy this guide then you might also enjoy our Inmarsat STD-C EGC Decoding Tutorial which has similar hardware requirements.
Outernet Setup: Patch Antenna -> LNA -> RTL-SDR with Bias Tee -> Raspberry Pi
Downloaded Files
Book Download
Video Download
Image Download
Hardware Guide:
The equipment required is very similar to what is needed for receiving Inmarsat STD-C. All the components required are cheap, and the whole system can be built for under $100 USD.
RTL-SDR Dongle.
Ideally our RTL-SDR V3 or an E4000 dongle. Other R820T/2 based RTL-SDR’s may fail at 1.5 GHz when they get warm. Outernet sell an appropriate E4000 dongle with bias tee built in on Amazon and on their store. They also have a E4000+LNA bundle available on Amazon.
You will need a dongle with a bias tee if you intend on using the Outernet LNA in mentioned in item 3. Our V2 and V3 dongles have a bias tee, and so do the E4000 dongles sold by Outernet.
L-band Antenna.
The Outernet signal requires at least a patch antenna to receive. Outernet are selling their own patch antennas on Amazon, and on their store directly. You can also build your own patch antenna, see Adam’s tutorial.
You could also use a homemade dish or helix antenna tuned for 1.5 GHz. Note that unlike in our Inmarsat tutorial the Outernet signal is a bit weaker and might be difficult to receive with a modified GPS antenna.
LNA + Filter. A low noise amplifier is almost certainly required to receive the Outernet signal. The LNA will reduce the system noise figure and boost the gain allowing for reception. A filter will reduce out of band interference. Outernet sell an excellent LNA with filter built in on Amazon and their store. Other LNA’s such as the LNA4ALL should also work, but we’ve found that we got the best performance at L-band with the Outernet LNA.
A Raspberry Pi 3, CHIP or Linux computer. Note that as far as we know only the Pi 3 is fully supported, although the Pi 2 is claimed to maybe work. For the Pi you will also need an 8GB+ micro SD card to install the software and OS on to. The CHIP is the famous $9 computer, but it is not released to the public yet and is estimated to ship in October 2016.
A smartphone/tablet/laptop/PC which has WiFi. This device will be used to connect to the Outernet WiFi hotspot server running on your Raspberry Pi 3 or CHIP.
After you have the pre-requisite hardware, the next step is to set up the software. Outernet uses a customized Raspbian operating system that they call “rxOS”. The latest images can be downloaded from https://archive.outernet.is/images/rxOS-Raspberry-Pi.
Installation on the Raspberry Pi 3 is as simple as burning the image file to an SDcard, and then inserting it into the Raspberry Pi 3. To do this you will need a microSD card (at least 8 GB), and a microSD card reader for your PC. To burn the image file follow these steps.
Setting it up on Linux is a fairly straight forward bunch of installation commands you need to run. The Linux set up guide can be found here and this should be compatible to run on a Virtual Machine if you are running Windows. Note that we had trouble with the installation on Linux when we tried it, but we believe that these problems will be fixed soon.
The Outernet demodulator running in Linux.
Finding the Outernet Signal and Testing Reception
Before actually running the Outernet software we’d recommend testing out your hardware first, to see if you can get reception of the Outernet signal in a program like SDR#.
Connect your system up like this Patch Antenna->Outernet LNA->RTL-SDR Dongle with Bias Tee->PC. Try to keep the amount of coaxial cable used between the patch antenna and LNA to a minimum, and if you must use long runs of coaxial cable, use high quality satellite RG6. Ideally, if you need coax cable, place it between the LNA and RTL-SDR dongle.
Find the frequency and satellite used in your country. More information about the satellites they use can be found here. Broken down into the main continents the satellites and frequencies are:
Americas: Inmarsat I4F3 – 1539.8725 MHz
Europe/Africa: Alphasat – 1545.94 MHz
Asian/Oceania: Inmarsat I4F1 – 1545.9525 MHz.
Now place the patch antenna on an outdoor surface which has a good view of the sky. Open up SDR# and ensure the bias tee is turned on and that the LNA LED is lit. Turn up the RF gain on the RTL-SDR. In SDR# tune to the frequency of the Outernet signal in your location. You should now be seeing a bunch of narrowband signals, with the Outernet signal at the center of the frequency you tuned to (note that if you are using an RTL-SDR without a TCXO, then the signal may be significantly offset). The image below shows what the Outernet signal and surrounding spectrum might look like on the Asia/Pacific Inmarsat I4F1 satellite.
If you don’t see the Outernet signal, or if it is very weak then you may need to point the patch antenna directly at the satellite to increase your signal. Pointing is likely to be needed if you are at a location far away from the equator. Precise pointing is not required, but pointing in the general direction can help.
To point the antenna we recommend downloading an Android app called “Satellite AR“. On iOS SatFinder 3D Augmented Reality may be a similar app, although we have not tested it. These are “augmented reality” apps which will overlay the satellite positions in the sky.
Finding the satellite position in the sky with the Android App “Satellite AR”
To use the app, first make sure that you are outside so that the app can get a good GPS lock which is required to determine satellite locations. Next open the app and press on the “Search satellite database” button on the top left. Type in the name of the satellite type used in your region (e.g. Inmarsat 4/Alphasat) and select it from the drop down list. Select the exact satellite in your region on the next screens. The camera should now be showing the location of the selected satellite, so point it to the sky and turn around until you see it. Next point your patch antenna towards the satellite. You may need to mount the patch on something sturdy to keep it pointed in the required orientation. Due to the circular polarization of the signal, the patch antenna should be oriented with the coax cable either pointing down or up, for best reception.
Running the Software
Once the software is installed on the Raspberry Pi 3 SDCard, or on the CHIP or a Linux PC and you have confirmed that you are receiving the Outernet signal you are ready to go! The Raspberry Pi 3 and CHIP units both broadcast a WiFi signal that allows you to connect to them from any WiFi enabled device that has a web browser. It is through this WiFi connection that you can control the Outernet receiver, and view any downloaded files.
If using the Raspberry Pi 3 or CHIP, plug in your RTL-SDR and set up your LNA and patch antenna to be in a spot that receives the signal well. Plug in the Pi3/CHIP unit into the power and wait a minute or so for it to boot and begin broadcasting its WiFi hotspot.
Grab your smartphone/tablet/laptop/PC with WiFi and search for the Outernet WiFi hotspot. Connect to it.
After connecting, a browser window should automatically pop up which will direct you to the Outernet logon page. If nothing pops up, open your web browser and browse to http://librarian.outernet.
Go through the Outernet account set up wizard, making sure to select the correct satellite for your location in the final step.
Once you’ve completed the set up the Outernet receiver should be set up and ready to go!
On the right hand side menu, choose Settings->Tuner settings and confirm that you are receiving with a decent SNR level of at least 3 dB. If not you may need to go back to SDR# and optimize your reception. Note that we have discovered that you may need to restart you Pi3 after creating an account if you don’t appear to be getting reception straight away.
To get back to the main Outernet page, browse back to http://librarian.outernet
Next we recommend leaving your Outernet receiver running for a couple of hours before checking back and seeing what files you’ve got. At a download rate of approximately 1 MB per hour, large files can take some time to download. Also note that the service is still in testing and development and is not constantly transmitting files at the moment, so it may take some time before you see a file actually being sent.
An example of some test files downloaded.
Now if desired, you can go to the Outernet upload page and upload a (small) file. Note that at the moment the file upload is still in testing, and is handled manually. But we tested this out with a small image file, and not long after uploading the file it was already received by our Outernet receiver. The file went from our PC to the internet, to their servers, was then broadcast up to the Inmarsat satellite in space, then broadcast back down to our Outernet receiver.
They write that in the future they hope to automate the file upload procedure and have the community decide by a voting system what files will be uploaded. These will probably be files like books, educational material or short videos intended to be broadcast to the regions with no internet. Those files will be uploaded on a basis of there being no guarantee when it will exactly be delivered. News, weather and ticker services like twitter feeds will be uploaded constantly and paying customers will probably be able to deliver a file on demand.
Currently Outernet is exploring ideas on what data to transmit and are looking for free news sources, as well as any sources that may allow the free retransmit of data like AIS and ADS-B. If you have any ideas on what they could transmit, contribute in their forums at discuss.outernet.is.
What else can be received with the Outernet hardware?
Inmarsat STD-C EGC is one service which provides messaging and text weather and situation updates for people at sea.
AERO is the satellite version of ACARS. Various aircraft messages can sometimes be heard. It is decodable with JAERO.
Over on hackaday.io there is a project blog for the “Distributed Ground Station Network”. This is essentially an idea to build a large network of distributed RF receivers which automatically receive signals from sources like cube satellites and other beacons. The project mainly uses RTL-SDR dongles at the moment for their RF receivers. In some ways it appears to be similar to the SatNOGs project which won the hackaday prize two years ago but the DGSN appears to be more focused on “reverse GPS” which allows the detection and tracking of the location of small satellite signals through distributed receivers.
They write:
The Distributed Ground Station Network (DGSN) is a novel network concept of small ground-stations and connected via the internet for performing automatic scans for cubesats and other beacon signals. By correlating the received signal with the precise, GNSS synchronized reception times of at least 5 ground stations, it enables the positioning of the signal’s origin. Thus a global tracking of small satellites becomes possible in this “reverse GPS” mode. It allows mission operators to position and track their small satellites faster after piggy-back commissioning, when the final orbit is yet undefined and could differ from the specified orbit. Furthermore it allows permanent communication in “data-dump” mode. In this mode, DGSN ground-stations relay the received data to the servers and thus to the operator. Let’s track everything, together!
ThumbSat is a company that aims to help experimenters design and launch experiments on their mini satellites (10x smaller than a regular cubesat with most of the same functionality) into orbit. They write that for about $20k they will fully design a satellite based experiment and launch it into orbit – all you need to do is provide the orbital experiment that you would like done.
To aide with the reception, they also have the ThumbNet project which aims to setup a network of satellite receivers around the world. They do this by providing school students around the world with low cost satellite receivers. The satellite receivers consist of modified/upgraded RTL-SDR dongles and satellite antennas.
Today the ThumbNet project announced the latest iteration of their RTL-SDR dongle, called the ThumbNet N3 SDR Receiver. This receiver has some interesting design changes when compared to any other dongle that we’ve seen so far. The biggest change appears to be that this dongle uses an external power port for power. They also replaced the 1.2V switching regulator with a 1.2V linear regulator for lower noise operation. This is useful because switching regulators can cause noise, whilst linear regulators are much cleaner. However, using a linear regulator increases the power consumption significantly, and the new dongle draws 450mA of current (vs 250-280 mA on standard or our V3 dongles), meaning that some USB ports may be unable to power the device unless the external power supply port is used.
The other interesting change is that they have changed the PCB form factor, and it can now fit into a common 1455 aluminum case. Also, similarly to our V3 RTL-SDR dongles, they have decided to add a common mode choke to the USB lines, which significantly reduces USB noise. To add ESD protection they also added a static bleed resistor. Finally, like their previous receivers they continue to use a F-type RF connector and a TCXO for frequency stability.
The price is $25.75 each plus flat rate global shipping of $4.50 and the receivers are expected to ship in mid-October. While we have not yet tested this model, it looks to be like a good receiver for those who need very low noise, or external power options.
They write:
The next Generation, ThumbNet N3 is designed from the ground up to be as simple to use as older generation dongles, but with powerful hardware features for advanced hobbyists and experimenters.
We removed all of the excess components that were sources of noise or interference in other dongles, and optimized the circuit for simplicity, sensitivity and selectability. Then we added a port to use a cable with the extremely common mini-USB connection so that the N3 is less prone to noise from the host computer than a traditional dongle. Finally, the use of standard Surface Mount 0603 or larger components makes it simple for testing or modification.
We built them for our own use, then decided to offer them to everyone.
A quick list of the features of the N3:
- Full backward compatibility with existing RTL-SDR dongles and software - High stability TCXO (+/-0.5ppm) (ensuring rock-solid stability from start-up and over a wide range of temperatures) - Standard R820T2 + RTL2832U (plus 24C02 EEPROM) chipset - Improved/enhanced decoupling. (Common-mode choke on USB port) - Low-noise, linear only power regulation (separate 1.2v and 3.3v regulators) - External DC (+5v, 450mA) supply connector - Mini-USB connection (allows easy separation of the RF unit from the noisy PC) - F type RF connector (very common and compatible with existing ThumbNet tracking stations) - Large (6x4cm) contiguous ground-plane (for better thermal dissipation) - Static drain-away resistor on the RF input (1K to ground) - All unnecessary parts (IR receiver, high-current LED etc.) eliminated to reduce parts count and noise - Circuit board can be mounted into a common 1455 case
Ideal for experimentation:
- Can be connected to an external power supply for very clean power - All of the important tracks are visible on the top side of the board for easy access - All of the RF parts are on the top of the board (only regulators and decouplers on the back) - Logical, simple layout using 0603 (or larger) SMT parts - IF port break in connector (between front end and IF/USB chip) provided
While not required for operation, the N3 receiver is designed to be able to utilize a clean source of power from an external 5v power supply, instead of using the noisy power line coming from the computer’s USB port. This gives a tremendous advantage to the purist or experimenter who wants to utilize power from the N3 to power any external experiments. (When the external power supply is active, no power is drawn from the USB port to power the N3.)
PLEASE NOTE: The N3 draws approximately 450mW of current and care should be taken, even when using a powered USB hub, as it could possibly exceed the current limit of the USB port.
The ThumbNet N3The ThumbNet N3 inside its optional 1455 aluminum enclosure.
Back in September we posted a tutorial that showed how to set up an Outernet receiver with a Raspberry Pi running their rxOS software and an RTL-SDR, LNA and patch antenna. Recently, Outernet have released a new decoder for Windows and Linux which is very easy to install and run. Outernet is an L-band satellite data service which can be received almost anywhere in the world with an RTL-SDR. They aim to be a “library in the sky”, constantly broadcasting public data like news, books, images/videos and other data files.
The new decoder is a Linux machine that runs in a self contained multiplatform Virtual Box virtual machine. This means that it is a standalone package, and it comes included with the OS, decoder, and all the files needed to make it run. Using a virtual machine eliminates any installation issues due to missing dependencies or libraries. Running the VM in Windows is as easy as double clicking on a .exe file to open it up. Note that you’ll need a relatively modern machine that supports hardware virtualization support (VT-x) (Core 2 or newer). The virtual machine itself is lightweight, and uses less than 50MB of RAM, and has very low CPU usage.
At the moment, the decoder writes files downloaded from the Outernet service to a directory stored in C:\Outernet\downloads. Unlike the Raspberry Pi decoder, there is no web interface for accessing the content, though this will probably be added in future builds. The files can be directly accessed in the Windows/Linux file managers.
To set up the VM on a Windows machine:
Download the Windows .exe archive and open it. When prompted, extract the files to a convenient folder on your PC.
Plug in your RTL-SDR and LNA, and set up your L-band antenna.
In the extracted folder run the outernet.exe file once. This will open the decoder and the first time it is run it will automatically create a folder in C:\Outernet.
If you are in the Europe/Africa and use the Alphasat satellite then you can ignore this step. If you are in another region, close the opened VM, then go to C:\Outernet\Satellites.Available, and then copy the file corresponding to the satellite used in your part of the world over to C:\Outernet\Satellites.Selected. Now reopen the outernet.exe VM.
The decoder should now be showing a good SNR value >2 in the top right information, and the State: should show FRAME LK. The bottom right window should also scroll “Packed written to socket.”
After a few minutes check the C:\Outernet\cache folder for pieces of files. Later check the C:\Outernet\downloads folder for completed files.
Further instructions can be found on their Windows Readme file. Note that as there is no web browser for the files, some will be downloaded as GZipped files, and will need to be unzipped to be viewed. For more information on the Outernet service as well as the hardware requirements see our previous tutorial.
We tested out the VM on a Windows laptop for a few hours and was able to receive several GZipped Wikipedia webpages as well as a photo, as shown in the screenshot below.
Files downloaded from Outernet (left). Outernet decoder running in VM (right).
A few weeks ago we posted about ThumbNets announcement of their new N3 RTL-SDR dongles. The main theme of their new dongles is lower noise as can be seen by their decision to disable the on board switch mode power supply and add an external power port for powering the dongle from a clean power supply.
Akos from the RTLSDR4Everyone blog received a prototype sample of the N3 for an initial review. In his review he shows some close up shots of the N3 PCB, and does a quick test on receiving some signals. His screenshots show that the noise floor is indeed very low, and that many noisy spurs are eliminated or at least significantly reduced.
Once ThumbNet release their actual commercial units we intend to produce our own review as well.
ThumbSat is a company hoping to enable experimenters to get low cost mini satellites into orbit for about $20k. To support the need for global RX of these satellites they have the ThumbNet project which utilizes RTL-SDR dongles as the receiver. They aim to provide schools and eligible volunteers around the world with free RX hardware to receive and record the data coming from these satellites.
If desired, Outernet also have a 
