Jenny first explains a bit about the impedance theory behind the design of coax connectors, before going on to introduce several coax connectors starting from the Belling-Lee connector which first came about back in the 1920’s and ending at the more modern SMA and MCX connectors. She then goes on to discuss how you should choose an appropriate coax connector for your application.
Recently Marek Sebera of ITDS Consulting wrote in to let us know about two new TETRA decoders that they have released. TETRA is a trunked radio communications system that stands for “Terrestrial Trunked Radio”. It is used heavily in many parts of the world, except for the USA.
The first piece of software released is called TETRA Listener and is from the Brmlab hackerspace in Prague. They write that Tetra-Listener is a new program (based on osmo-tetra) that can decode unencrypted voice and data traffic. They also write that it is very easy to set up and install since it uses Vagrant, which is a system that can be used to automatically set up a VMWare or VirtualBox Virtual Machine that has everything set up and ready to go. The instructions for using the software can then be found in the readme of the main tetra-listener page on GitHub.
The second software they have written is what they believe is the world’s first open source TETRA Multiframe SDS decoder. SDS stands for short data service and is the TETRA equivalent to SMS text messages used on a GSM network. They write that their solution can assemble long multiframe SDS messages.
Previously we showed how unencrypted TETRA messages could be listened to using telive in our tutorial. It is good to see alternative solutions now coming out, and in the future we hope to test this new software out.
The software defined radio academy is a sub-conference held during the HAMRADIO conference at Friedrichshafen, Germany. HAMRADIO is the largest Amateur Radio yearly convention held within Europe. This years conference has completed and now several SDR related talks have been uploaded to YouTube. Many of the talks discuss the latest developments in SDR technology and projects. An example of some talks we enjoyed are shown below, but we encourage you to check out the YouTube link and watch any of the talks that interest you.
Bastian Blössl, DF1BBL: Signals Analytics with Radio Controlled Key Systems
In this talk we will go through the complete process of reverse engineering an unknown digital signal. Although a widespread car key fob from Hella will serve as an example, the aim is to provide a generally applicable walk-through. To decode the signal we will user different tools to determine its frequency, modulation, encoding, and finally its frame format. More specifically, we will use fosphor, baudline, gqrx, and audacity to study the signal in time and frequency domain. Even though we will just have a quick glance at the different applications, the goal is to show they capabilities and more importantly how they can be combined. Once we figured out the waveform and its parameters, we will go ahead an build a receiver in GNU Radio. GNU Radio is a real-time signal processing framework that already provides all means to demodulate the signal and produce a bit stream. At this point we will use command line tools and simple python scripts to study the bit stream to derive the frame format. Finally, we add a small technology specific block to GNU Radio that decodes and parses the frames to build a complete receiver. Hopefully, this will provide some hands-on experience and give an overview over the various tools that are available to study and decode the signals out there.
Bastian Blössl, DF1BBL: Signals Analytics with Radio Controlled Key Systems
Dr. Howard White, VE3GFW: Four Generations of SDR Architectures and Products
In the Past Year, a new 4th Generation SDR Architecture has emerged that not only bests Legacy Radios with better performance but has ergonomic advantages so that Contesters and DXer’s can finally make SDR’s their first choice. The talk will cover the rapidly accelerating pace of evolution of SDR Technology through Four Generations of SDR Architectures with examples of Amateur Radio products using each architecture.
SDR Technology has captured the imagination of Amateur Radio Operators who increasingly chose SDR’s when buying a new radio. This trend has become so dominant in the USA that Legacy Radio Manufacturers have started to mislabel Legacy Radios as SDR’s to try to recapture lost sales from the uninformed. The presentation will define what is an SDR and show where Legacy technology is not an SDR.
There are now Four Generations of SDR Architectures. First Generation SDR Architectures became economically and technologically feasible for amateur radio applications around 2000. Since then the pace of evolution of Amateur Radio SDR Architectures has begun to accelerate rapidly with Second Generation Architectures emerging in 2009, Third Generation Architectures in 2012 and most recently the very exciting Fourth Generation SDR Architectures in 2014. The presentation will define each of these architectures, explain how technological developments have caused them to happen and review the strengths and weaknesses of each architecture.
In order to make the presentation relevant to Amateur Radio Operators, the presentation will include products (with relative pricing where practical) currently on the market that are representative of each of the SDR architectures. Perhaps the most exciting development for amateur radio operators in the past year has been the emergence of a new 4th Generation SDR Architecture that not only bests Legacy Radios with better performance but has ergonomic advantages so that Contesters and DXer’s can finally make SDR’s their first choice.
Dr. Howard White, KY6LA: Four Generations of SDR Architectures and Products
Martin Dudok van Heel, PA1SDR: Passive Radar at home
This talk is about using the reflections of FM-radio and GPS satellites signals to do passive radar.
With passive radar you can analyze everything that reflects radiowaves without transmitting anything yourself. The airplanes, cars, buildings, amount of rainfall, the condition of the atmosphere layers, ionized gases, landscape layout, ocean waves, meteorites or individual humans or machines moving inside or outside buildings. Even most stealth airplanes can be detected by passive radar when the signals of distant transmitters are reflected down to the receiving passive radar station.
With the building blocks, normally used for implementing Software Defined Radio Systems you can also do very interesting signal analysis. You can use the opensource toolkits GNU Radio (SDR) + Octave (math) + your own code to analyze the direct path and reflections of any kind of wireless signal. You can use this to do passive radar, which is the art of generating a radar image by analyzing the reflections of signals you have not transmitted yourself. You need to be able to somehow obtain an estimate of the original transmitted signal without reflections, and compare/correlate that to the signal with reflections. Then use the time of arrival, phase, Doppler shift and direction of arrival to determine the exact location, speed and strength of (the source of the) refection, and thus generate a passive radar image.
Martin Dudok van Heel, PA1SDR: Passive Radar at home
András Retzler, HA7ILM: OpenWebRX, a Multi-User, Web-Based SDR Receiver Application
Software Defined Radio technology is getting more and more popular among amateur radio operators and hobbyists, as several different universal SDR receiver devices have become available recently. OpenWebRX is a software made for those who want to set up remote SDR receiver stations accessible from the web. It has been developed with open-source codebase, multi-user access and easy setup in mind, to be an alternative to other similar projects (WebSDR, ShinySDR, WebRadio, etc.) It also supports cheap RTL2832U based tuners. Basically, OpenWebRX is an on-line communications receiver for analog modulations (AM/FM/SSB/CW), with a web UI on which real-time waterfall display is available. Users can select a channel within the bandwidth of the sampled signal acquired from the SDR hardware. The selected channel is demodulated on the server and the resulting audio is streamed to the browser of the user, where it is played back. Users can set receiver parameters (channel frequency, modulation mode, filter envelope) independently. OpenWebRX was written in python and JavaScript. The web interface supports multiple browsers and uses modern browser features introduced in HTML5. The digital signal processing functions were placed in a separate library, libcsdr, which has been implemented in C and can also be considered useful as a standalone package. It can perform digital downconversion, filtering and demodulation tasks on I/Q data.
András Retzler, HA7ILM: OpenWebRX, a Multi-User, Web-Based SDR Receiver Application
Over on his blog András Retzler has created a post that discusses his research work on creating a fast networked wideband HF receiver. András is the creator of the web based OpenwebRX software, which allows RTL-SDR and some other SDR’s to efficiently broadcast their SDR data over a network and onto the internet. Some live SDR’s can be found at the OpenWebRX directory at sdr.hu.
The problem with the current implementation, András writes, is that while OpenWebRX works well with the RTL-SDR’s 2.4 MSPS sampling rate, it can not work so well with very high sampling rates, such as 60MSPS due to excessive computational requirements when several channels need to be monitored. András’ solution is to use his Fast Digital Down Conversion (FastDDC) algorithm which is significantly more CPU efficient. András writes that the FastDDC algorithm improves computation by up to 300% in some cases, can speed up calculations on low powered computers like the Raspberry Pi 2 and can be implemented on a GPGPU for even higher performance. He is still working to implement the algorithm in OpenWebRX.
John Seamons has forked OpenWebRX, and sells his own hardware with it. The web interface is clearly the selling point of the device. After getting a lot of help from me, most of which was inevitable for his success, now John and ValentF(x) are leaving me with nothing, except a ‘Thank you!’. John has told me that OpenWebRX is a large part of his project, and he also claimed that my work has reduced the time-to-market of his product by maybe a year or so.
Why I’m standing up here is that forking open source software (which means changing the code in a way that is incompatible with the original version, and taking development in another direction), and funding it through Kickstarter is a very unusual way of getting things done. I acknowledge that John has very much work in his board and the accompanying software, however, he treated me and my project in an unethical manner.
In the Kickstarter comments section, the KiwiSDR creators reply back with their side. It is hard to say who is in the right in a situation like this. While what KiwiSDR have done is legal according to the licence, the ethics of doing so are questionable. We hope that both parties can successfully come to an agreement in the end.
If you want to directly support András and his work on OpenWebRX and other projects like FastDDC, then please consider donating to him at http://blog.sdr.hu/support. If you are a KiwiSDR backer, donating to Andras may be one way to right the situation if a deal cannot be reached.
JAERO is a program by Jonti that was released late last year which allows us to use a SDR such as an RTL-SDR to receive L-band and C-Band AERO messages. 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. The C-band signals are the air to ground portion of AERO and more difficult to receive as they require an LNB and large dish. However they are much more interesting as they contain flight position data, like ADS-B.
If you enjoy JAERO, please remember consider donating to Jonti.
Plotting flight positions that are out of regular ADS-B range. Demodulated from C-Band AERO signals with JAERO.Monitoring two C-Band channels in SDR# with the AUX VFO plugin.
Over on the RTLSDR4Everyone blog author Akos has uploaded two new posts. In the first post he discusses his opinion on the recently announced FlightAware ADS-B Optimized ProStick, which is an RTL-SDR with an 1090 MHz optimized LNA built into the front end. He writes that he believes that the claimed 30% increase is not possible with the ProStick as his own tests using an LNA4ALL at the front end only showed a 10% increase in range at most. In his post he also shows that the updated Nooelec R820T2 stick comes with a suction cup holder for it’s supplied antenna.
To add to his post, while we haven’t received the ProStick unit we bought for review yet we believe that the ProStick will improve ADS-B reception a certain amount in some situations, especially for those using the stick in such a way where it is placed right at the antenna, or with a small desktop style antenna with little coax, both with an appropriate ADS-B filter used. However, as Akos also suggests in his post we believe that the superior solution is an external type LNA, like the LNA4ALL.
The rtl_power program allows you to use the RTL-SDR to perform a power scan over an arbitrarily large portion of the frequency spectrum (within the RTL-SDR’s supported frequency range) by hopping over ~2 MHz swaths of bandwidth. The updated rtl_power_fftw software was originally written by Klemen Blokar and Andrej Lajovic and is an update over the regular rtl_power program. It uses a faster FFT processing algorithm and has several other enhancements that make it more useful for radio astronomy purposes.
-e param for session duration this allows to specify the recording duration in sec, mins… etc just like it was possible with rtl-power
-q flag to limit verbosity this will allow the various printouts to happen only the first time and not on every scan
-m param to produce binary matrix output and separate metadata file this will get a file name (no extension) and use it to store the power values in binary format within a .bin file + a metadata text file with .met extension
Summary of my requirements:
I wanted to leverage the ability of rtl-power-fftw to specify N average values to integrate for less than 1 second when needed. Plus running multi-MHz scans and storing for several minutes.
I wanted to use a binary format instead of the .csv one in order to obtain the smallest possible size since I’m logging all the night long (CSV’s blank delimiters and decimal dots were wasting my precious microSD space)
keep high the precision on decimal digits saving float values (could be important for other usages)
obtain a complete stream of binary values representing all the bins for each scan, one scan after the other, in a matrix like organization
…that would allow me to plot the waterfall extremely fast with gnuplot
…and then add specific annotations and file properties/metadata in a more convenient way using python
Example rtl_power_fftw output: A scan of Jupiter’s radio emissions.
Unsurprisingly the results clearly show that the Airspy receives ADS-B signals significantly better than the RTL-SDR. However, what comes as a surprise is that it is actually appears to be outperforming the dedicated Beast receiver. In the tests with the outside vertical antenna, the Airspy running on a Raspberry Pi appears to receive a significant higher number of messages and also sees planes out to a further range.
Not too long ago the Airspy team released their ADS-B software for the Raspberry Pi 2. They write that this software uses the full 10 MHz bandwidth and can even decode messages that are overlapping one another. We’ve also been told by the Airspy team that the Airspy is already in professional use as an ADS-B receiver amongst several small airports.
In the future we hope to compare the Airspy against the RTL-SDR on ADS-B reception ourselves, and also compare it against the 8 MHz bandwidth SDRplay whose development team have also recently released a new ADS-B decoder, as well as the recently released FlightAware ADS-B Prostick RTL-SDR.
