One problem that sometimes arises when using embedded single board computers like the Raspberry Pi is that they often cannot provide enough current to power devices through the USB port.
Over on YouTube user KD9 BVO wanted to use his RTL-SDR with a Raspberry Pi, but found that the Raspberry Pi shut down whenever he plugged it in, due to it using too much current. To get around this problem he decided to build a DIY powered USB hub. This solution allows the RTL-SDR to be powered via the hub itself, rather than through the Raspberry Pi USB port.
In the video he takes an existing unpowered hub and shows how to modify it to provide power directly to the RTL-SDR via an external power supply.
Over on YouTube user Mile Kokotov has uploaded a video showing him receiving a WPX CQ CW (morse code) contest on his SDRplay RSP. The SDRplay RSP is a $149 USD software defined radio with a tuning range of 0.1 – 2000 MHz, 8 MHz maximum bandwidth and 12-bit ADC.
In the video Mile shows that the SDRplay is capable of receiving many strong closely spaced CW signals at the same time as weaker ones without overloading. He uses the HDSDR software and a large 43.1m long delta loop antenna strung up in his backyard.
Adam 9A4QV has once again uploaded three new videos to YouTube, all related to L-band satellite reception. The first video shows how much L-band reception can be improved by using two LNA4ALL low noise amplifiers together with a filter placed in between them. Using two LNA’s instead of one improves the reception by about 2-6 dB. He also shows that L-band Inmarsat satellite signals at 1.5 GHz can even be received by his 1090 MHz folded monopole ADS-B antenna placed indoors.
The second video shows a reception report of the new Outernet signal. The Outernet signal is a new satellite data service being provided that broadcasts up to date news as well as various files and information such as educational videos and books for people in third world countries without internet. They have said that they are working on free decoding software for their service which should be released soon. The Outernet signal is a bit weaker than typical AERO signals, but can still be received quite easily with an RTL-SDR, patch antenna and 2 x LNA4ALL. The Outernet downconverter mentioned in a previous post should of course also work well.
His third video shows some tests on his L-band filter, showing return and insertion loss.
Dejan Ornig, a 26 year old student at the University of Maribor’s Faculty of Criminal Justice and Security was recently almost jailed for finding a security flaw in Police TETRA communications in his home country of Slovenia. Back in 2013 his University Computer Science class of 25 was assigned a task to research security vulnerabilities in TETRA. TETRA is a RF digital communications protocol often used by authorities due to its ability to be secured via encryption. During his research he used an RTL-SDR and the open source Osmocom TETRA decoder, and discovered a flaw in the Slovenian Police’s TETRA configuration which meant that encrypted communications were often being broadcast in the clear. Translated, Ornig said:
For $20 I bought a DVB-T receiver (RTL-SDR), on the Internet, I have found also freely available and open-source software OsmoCOM. Free access solution for decoding the signal Tetra eighth-tetra is already prepared in advance programming framework based on the platform GNU.
He goes on to say (translated):
I was even more surprised when I found that most users do not have authentication turned on the radio terminal, even though the Ministry of the Interior in the documents and tenders repeatedly wrote to all the radio terminals to access networks using authentication.
Shortly after discovering the flaw, Dejan privately contacted the authorities with his findings. But after two years of repeatedly contacting them and waiting for a fix, Dejan decided to take his story to a local news agency in February 2015. At this point the Slovenian Police became interested in Dejan, and instead of fixing the problem, decided to conduct a search on his house, seizing his computer and RTL-SDR. After the search the Police made life harder for Ornig by trying to lump on other problems. During the search they found a “counterfeit police badge” in his house and apparently accused him of impersonating a police officer, and after a search of his PC they also decided to charge him after finding out that he covertly recorded his ex-employer calling him an “idiot”.
Ornig has now been given a 15 month suspended jail sentence for attempting to “hack” the TETRA network. Fortunately the suspended part means that in order to not go to jail Ornig simply must not repeat his crime again within 3 years. While SDR’s and radios are not illegal in most countries this is a reminder to professional and amateur security researchers to check that what you are doing is legal in your country. Even if it is for the overall good, Police often do not have the technical competence to understand security researchers and may react illogically to findings. The good news about Ornig’s story is that apart from the suspended jail sentence the authorities appear to have now worked with him to fix the problems.
Over on YouTube Adam 9A4QV has uploaded a video showing how good L-band reception can be with only a cheap home made patch antenna, RTL-SDR dongle and LNA4ALL. The video is in response to a question on our previous post, which discussed the prototype Outernet downconverter. The question asked what difference can we expect with the downconverter compared to just using an LNA, like the LNA4ALL.
In the video Adam shows that L-Band reception with the LNA4ALL can be as good as with the downconverter. The main problem with L-band reception on the RTL-SDR is that some units tend to fail to receive properly at around 1.5 GHz. The downconverter bypasses this problem by receiving L-band at around 200 MHz instead. Though we believe that this problem is solved on the units we sell as we heatsink to a metal enclosure, and if that is not enough, it can be solved further by using this modified driver. The other advantages of the downconverter is that it includes filtering, an LNA, and allows you to use much longer runs of lossy cable, which is useful if for instance you want to put a permanent L-band antenna on the roof.
In the HF region between about 0 – 30 MHz it is common to see and hear “chripers” – signals which quickly sweep through the HF frequency band and produce an audible chirp. These chirps are actually signals from Ionosondes which is a type of radar system used to monitor the Ionosphere. The Ionosphere exists about 50km above the surface of the earth and is the atmospheric layer responsible for a large part of long range HF communications. In a previous post by Mario Filippi we also discussed Ionosondes.
Usually it is scientists who transmit and monitor these Ionosondes, however if you have wide band radio that can cover a majority of the HF spectrum then you can also monitor these chirpers yourself. Over on his blog Fabrizio Francione has created a post showing how to use a USRP, together with a GNU Radio Program called GNU Chirp Sounder to create his own amateur Ionogram monitoring station. The USRP is a fairly expensive SDR with a bandwidth of 25 MHz, but we add that we think that next generation of low cost wide band SDRs like the up and coming LimeSDR should also be able to do the same job.
The Ionograms show at what frequencies HF propagation is currently optimal for a specific distance (or number of signal bounces from the Ionosphere). Below is an example Ionogram animation showing the reception of Ionosondes taken over time. Video from the GNU Chirp Sounder page.
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.
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).
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