Thanks to OH2BNF for writing in and sharing his plan to build a "Large Scale Raspberry SDR" (LSR-SDR), which will be based on RTL-SDR dongles. To create the LSR-SDR he plans to take a 19" rack which can support up to 40 Raspberry Pi 3's, plus up to 160 USB devices, and turn it into a massive SDR array. The rack is key as it allows for simple power management of all the Pi's and other devices to be connected.
OH2BNF plans to connect 20 or so RTL-SDRs, with some operating individually and with others operating coherently via a common external oscillator. The rack may also contain some transceivers, an ICOM IC-7300, antenna switches, upconverters, LNAs and other hardware too. Once completed he hopes to move the system to a low RFI environment and operate the unit entirely remotely. With this he hopes to solve his local RFI issues. He also writes regarding applications:
Primary objectives are to incorporate automated adaptivity to the system at large – for example leveraging on band condition information, WSPR (Weak Signal Propagation Report) & friends, automated signal detection and decoding, great flexibility in terms of individual cluster nodes being able to fast respond to various needs and tasks, strong emphasis in parallel processing where applicable depending on the problem type and dataset, support for multiple end users benefiting from the computing and reception capacity of the cluster – to name the most significant.
It's an interesting idea for sure, and we hope to see some updates from OH2BNF in the future.
Thank you to RTL-SDR.com reader 'JJ' for writing in with a submission for his Lego Pi Radio. JJ's Lego Pi Radio consists of a Raspberry Pi and RTL-SDR and is designed to be an FM Radio, MP3 and internet radio player all in one, with a cute enclosure made out of Lego bricks. The radio is controlled by an external numpad which allows for a number of presets to be chosen from.
The internet radio and MP3 players are handled in software by VLC player and a script written by JJ is used to map the numpad to RTL-SDR FM presets, or MP3 and internet radio functions. The whole unit is run headless and if anything needs to be updated such as internet radio links, JJ simply accesses the unit via an SSH shell. JJ also writes how he had to try 3 different brands of speakers before he found one that could be driven directly from the Pi with adequate sound quality. In the future he hopes to add a bluetooth remote.
One problem that JJ found was that the standard rtl_fm did not produce high quality audio. Fortunately he found the NGSoftFM software which is capable of outputting high quality FM stereo sound and is compatible with RTL-SDR dongles.
In the past we've seen a similar project that was implemented on a BeagleBone Black. The idea in that project was to switch between FM and internet radio depending on the reception quality.
Last year we posted about QuestaSDR, which is a simple SDR multi-mode GUI that is compatible with the RTL-SDR. Since then QuestaSDR has evolved, and is now available on Android devices as well. It looks to be a nice alternative to RF Analyzer and SDR Touch which are the most popular RTL-SDR Android apps. The description of Android QuestaSDR reads:
QuestaSDR - powerful and flexible, cross-platform Software Defined Radio Application (SDR). Built-in scheduler architecture provides integrate plugins, plugins kits and multi - UI. Typical applications are DXing, Ham Radio, Radio Astronomy and Spectrum analysis.
Support Hardware: - RTLSDR Dongle
Main features: - Dark, Ligth, Universal, Material application style - Many spectrum settings (FFT size, waterfall FPS and color theme) - AM/SSB/NFM/WFM demodulator - RDS decoder - Record AF file - Frequency bookmarks - Web remote - Supported IF-adapter, upconverter, downconverter hardware - Rig samplerate, frequency, level and iq disbalance calibrate
To start using QuestaSDR, you will need: - RTL-SDR dongle - USB OTG Cable - used to connect a RTLSDR to your Android device.
Connect the USB dongle to the USB-OTG, then insert the free end of the cable into the USB port of your Android device and launch the QuestaSDR! Now you can listen to live frequency range shortwave, VHF, UHF.
Feedback and bug reports are always welcome.
Please note that I am not responsible for any legal issues caused by the use of this application. Be responsible and familiarize yourself with local laws before using.
The software is based on the set up from this excellent tutorial, which creates scripts and a crontab entry that automatically activates whenever a NOAA weather satellite passes overhead. Once running, the script activates the RTL-SDR and APT decoder which creates the weather satellite image. He then uses some of his owns scripts in Twython which automatically posts the images to a Twitter account. His Twython scripts as well as a readme file that shows how to use them can be found in his Google Drive.
Over on YouTube user AE0AI has uploaded a video where he explains how he uses an RTL-SDR and a home made noise source as a poor man's network analyzer. A network analyzer is a tool that allows you to analyze the response of RF devices, such as filters. By using a noise source together with an RTL-SDR the same functionality as a network analyzer can be obtained, however of course with less accuracy.
In the video AE0AI shows us his home made noise generator, which is a based on a simple circuit that he found online. He then shows the noise generator connected to the RTL-SDR, which shows that his home made generator works up to about 40 MHz. Later in the video he tests a home made 40m filter with the noise source and RTL-SDR, and the response is easily visible. With the response visible he is able to tune the filter by adjusting the inductor windings.
In a previous post back in September 2017 Stefan Scholl (DC9ST) treated us to a very interesting write up about how to localize transmitters to within a few meters using time difference of arrival (TDOA) techniques with multiple RTL-SDR dongles spread out over an area.
- What signal parameters influence the quality of the correlation? - Which type of correlation calculations are available (four) - Which are suitable with RTL-SDRs, considering noise and phase and frequency offset?
Stefan writes that his findings could be interesting to people interested in the following techniques:
- TDOA localization - Synchronizing several RTL-SDRs - Passive Radar
Over on his site, Clem the author of the QIRX SDR software package has written up a three part series where he explains an ultra-fast and very accurate method for calibrating the frequency offset of RTL-SDR receivers by using DAB signals. If you are unfamiliar with DAB, it stands for 'Digital Audio Broadcast' and is a type of digital radio station available in multiple countries in the world, especially in Europe. However it is not used in the USA. Clem writes:
I wrote a three-part tutorial about an ultra-fast, generally available (where you have DAB reception) and very accurate method to calibrate RTL-SDR receivers. It is called "Tutorial: Calibrate your RTL-SDR in 15 Seconds", http://softsyst.com/QIRXCalibrate?sequenceNo=0. It is using the frequency of a DAB transmitter as the reference signal, and is coming in three parts:
· Part I: Method and Measurement, describes the method (example) and compares it to two other, well-known methods.
· Part II: Checks, Frequencies, Sampling Rates: Tells how to make plausibility checks on the obtained calibration result, goes into the foundation of different measuring methods, and explains why calibrating a receiver is generally beneficial, not only for DAB purposes (where at least the frequency correction is mandatory).
· Part III: Improving DAB, Tells why it is advantageous for DAB reception not only correcting the frequency, but also the sampling rate (which is often omitted).
Part I and Part II of these are already on our website, Part III will come soon.
Over on YouTube Corrosive has uploaded a new video where he explores CubicSDR, and explains all the windows and settings that it has. CubicSDR is a free RTL-SDR compatible cross-platform open source multi-mode SDR application, similar in nature to SDR#, HDSDR SDR-Console etc. It's quite popular due to it's multi-platform nature, meaning that it can run on Windows, MacOS and Linux.