Recently SV3EXP wrote in to let us know that he has been documenting his experiences with trying to get aisdecoder to decode both AIS channels simultaneously. AIS stands for Automatic Identification System, and is a system used to track the locations of marine vessels. With an RTL-SDR or other SDR radio, and appropriate decoder software you can plot ship positions on a map. As the AIS system uses two separate channels for redundancy, you can get a faster and more reliable update rate if you monitor and decode both channels.
Of course the easier solution to decode both AIS channels at once is to use decoding software that already supports this, such as AISdeco2 or AISrec which can be downloaded at http://xdeco.org, and https://sites.google.com/site/feverlaysoft respectively. But regardless SV3EXP's method does show an interesting way to demodulate multiple streams using only command line tools.
SV3EXP also wanted to point out that he is selling a bias tee powered PSA4-5043+ based LNA on eBay which is compatible with the bias tee on our RTL-SDR Blog SDR units.
APCO P25 is a digital voice signal and is commonly used like public safety departments such as police and fire. With an RTL-SDR and the open source Linux based OP25 decoder these signals can be decoded, assuming they are unencrypted. Software like DSD+ can also be used, but OP25 can supposedly decode more systems. Before the RTL-SDR, hardware scanners like the $~360 USD Uniden BCD996T digital scanner radio were typically used.
Over on YouTube user Rob Fissel has uploaded a video showing a comparison between an RTL-SDR using the OP25 decoder and a Uniden BCD996T. Both radios are used to decode a weak P25 Phase 1 LSM signal. He uses a Scantenna antenna with an antenna splitter to run both radios at the same time. His results show that even though the constellation is poor, OP25 does a good job at decoding the signal and producing voice, whereas the BCD996T doesn’t even manage to hear the control channel.
Akos of the rtlsdr4everyone blog has recently written up a comparison of the RTL-SDR and SDRplay. The SDRplay is a $149 USD software defined radio with a 100 kHz to 2 GHz frequency range, a 12-bit ADC, and up to 8 MHz of bandwidth. It now competes heavily with the $99 Airspy Mini which is a similarly specced SDR.
Akos compares the two units and comes to the conclusion that the RTL-SDR is still the best choice for beginners, but that the SDRplay is definitely a good choice if you have good antennas in place and if the receiver is the major bottleneck in your setup.
In his review he goes over several points covering the costs involved, aesthetics, customer support, PC hardware requirements, setup, operation and finally reviews the performance of the SDRplay. His results show that the SDRplay generally receives much better than the RTL-SDR, but has some problems with broadcast FM imaging.
An updated set of windows binaries and build scripts have been posted. Quick summary:
1- Added gqrx to package 2- Patched 2 x issues which would cause the generic version to crash on non-AVX systems (one in volk, one in FFTW) 3- Added gr-newmod to package
Plus a number of improvements to make the scripts more robust.
To run GNU Radio for Windows you will need a 64-bit version of Windows 7/8/10. It appears that the installation is as easy as running the installer and waiting for it to download and install the 1.7 GB worth of files.
Also, over on his blog author designing on a juicy cup posted about how he’d been able to get the GNU Radio Windows binaries to run a ATSC HDTV decoder from a file recorded using an SDRplay RSP (ATSC is too wideband for an RTL-SDR to decode). ATSC is the digital TV standard used in North America, some parts of Central America and South Korea. He writes that one advantage to using GNU Radio on Windows is the ability to use a RAM drive for faster file processing.
Back in November 2015 we posted about Disney Research’s EM-Sense which was an RTL-SDR based smart watch that was able to actually sense and detect the exact (electronic) object the wearer was touching. It worked by using the RTL-SDR to detect the specific electromagnetic emission signature given off by various different electronic devices.
The Disney research team have put forward the idea that a low cost SDR like the RTL-SDR can be used in place of RFID tags when they would have been used to identify electronic devices. The idea is that the SDR can be used to read the electromagnetic emissions of the electronic device, which can then be used to identify the item, thus eliminating the need for an RFID tag or barcode. Their abstract reads:
Radio Frequency Identification technology has greatly improved asset management and inventory tracking. However, for many applications RFID tags are considered too expensive compared to the alternative of a printed bar code, which has hampered widespread adoption of RFID technology.
To overcome this price barrier, our work leverages the unique electromagnetic emissions generated by nearly all electronic and electromechanical devices as a means to individually identify them. This tag-less method of radio frequency identification leverages previous work showing that it is possible to classify objects by type (i.e. phone vs. TV vs. kitchen appliance, etc). A core question is whether or not the electromagnetic emissions from a given model of device, is sufficiently unique to robustly distinguish it from its peers.
We present a low cost method for extracting the EM-ID from a device along with a new classification and ranking algorithm that is capable of identifying minute differences in the EM signatures. Results show that devices as divers as electronic toys, cellphones and laptops can all be individually identified with an accuracy between 72% and 100% depending on device type.
While not all electronics are unique enough for individual identifying, we present a probability estimation model that accurately predicts the performance of identifying a given device out of a population of both similar and dissimilar devices. Ultimately, EM-ID provides a zero cost method of uniquely identifying, potentially billions of electronic devices using their unique electromagnetic emissions.
An EM-ID use case: Identifying difference laptop assets.
In the paper we can see that the EM-ID hardware is essentially just a direct sampling modified RTL-SDR and antenna. The RTL-SDR is modified to use direct sampling as this allows it to receive 0 – 28 MHz, and thus 0 – 500 kHz where the most useful EM emissions exist. The system process is to basically scan the device using the antenna and RTL-SDR, extract features such as power peaks from the recorded EMI spectrum and then turn this data into a device signature which can then be used to compare against a database of previously recorded and known device signatures. (e.g. light bulb, iPhone).
The EM-ID Hardware: Essentially an RTL-SDR and antenna.The EM-ID Process.
The LimeSDR is a new transmit capable software defined radio with a 100 kHz – 3.8 GHz frequency range, 12-bit ADC and 61.44 MHz bandwidth which is currently seeking crowdfunding.
A few days ago the LimeSDR crowdfunding campaign went live, and within the first 32 hours all 500 of the $199 USD discounted early bird LimeSDR’s were grabbed up. Since then the crowfunding momentum has unfortunately slowed considerably. However, in an attempt to possibly revitalise the campaign LimeSDR has released a second batch of early bird units which are selling for the $50 discounted price $249 USD. They also write that people who already backed at the higher regular price of $299 USD have automatically been converted to the $249 USD price. At the time of this post there are still 427 early bird units remaining.
We think the LimeSDR has the potential to be a significantly better version of the HackRF and bladeRF which would sell for the same price or even less in the future, so please consider backing the project if an SDR like this interests you.
Their press release reads:
First, a big thank you to all our backers. With your support, we hit 20% of our campaign target in just over 24 hours and all 500 of the first flock of early bird boards were pledged within 32 hours. This is phenomenal! We have been blown away by the support and excitement from you, our community. Thank you!
Our mission is to democratise wireless innovation. Anybody should have access to this technology and be able to create innovative, game changing solutions. The level of support we have received from all of you has gone a long way to reassure us that we have made a great start in achieving our mission.
We are now confident that the LimeSDR campaign can jump start this democratisation. When we successfully reach our target and have delivered on our commitment, the work doesn’t stop there either. We will continue to work on the LimeSDR platform to improve it, together with the help of the community.
We are also working with the key players in the wireless industry and have been partnering with innovators and organizations, including EE/British Telecom, who share our vision to bring the power of open source innovation to wireless communications in a way that has never been done before.
As a result of the early success of our campaign, we are gathering further support from our manufacturers and suppliers and are now able to offer new pledge levels, including an additional flock of 500 early bird LimeSDR boards boards at a reduced price of $249. This is a significant reduction from the retail price of $299. Those who have already signed up for the $299 LimeSDR will instead pay the reduced price – your order will be amended and an updated order confirmation email will be sent to you within the next 24 hours.
We have big announcements in the pipeline, and our plan is to send you regular updates throughout the campaign. These will include exciting partnerships and new pledge levels as we see the growth of our supporters. Stay tuned!
The RTL-SDR can be used for many interesting radio astronomy applications such as observing the Hydrogen line. Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). Normally a single hydrogen atom will rarely emit a photon, but since space and the galaxy is filled with many hydrogen atoms the average effect is an observable RF power spike at 1420.4058 MHz. By pointing a radio telescope at the night sky and integrating the RF power over time, a power spike indicating the hydrogen line can be observed in a frequency spectrum plot.
On his website Steve Olney has been writing about his experiments and results with using an RTL-SDR to observe the hydrogen line. On his website he writes that he uses a 3M dish, with an LNA at the antenna to reduce the system NF, a hydrogen line tuned bandpass filter to remove out of band noise, 2 line amps to overcome coax loss, and finally a second LNA just before the RTL-SDR dongle to optimize the signal strength for the ADC. The dongle he uses has been modified to use a TCXO, and is aircooled via a PC fan. He also uses a modified version of the rtlsdr.exe IQ file recorder and his own custom GUI for controlling the RTL-SDR and antenna tracking mechanism.
His results show that he was able to detect the Hydrogen in the Large and Small Magellanic clouds. He also shows a method for converting the 8-bit IQ data down to 1-bit to save disk space, and shows that while some noise is added, the overall result is preserved.
See the related posts for other hydrogen line experiments with the RTL-SDR.
The 3M dish used for hydrogen line detection.The fan cooled RTL-SDR used to detect the Hydrogen line.
Over on YouTube user Lan Party Hosting has uploaded a video showing a comparison between the RTL-SDR and SDRplay. In his tests he receives various HF and VHF/UHF signals and records their SNR values in a spreadsheet which can be downloaded here. The results show that as expected the SDRplay generally outperforms the RTL-SDR. However his results surprisingly show that the SNR of the RTL-SDR is usually better when the front end LNA of the SDRplay is not used, though we’re not sure if he took into account the difference in visual SNR that can be caused by using different bandwidths.
The video and measurements also explain when and why you should the Low IF mode on the SDRplay instead of the Zero IF mode to reduce signal imaging.
