DSD+ (Digital Speech Decoder+) is a popular Windows tool that can be used together with an RTL-SDR to decode digital speech signals such as P25 and DMR. There is unfortunately no version for OSX.
However, recently on YouTube user Matthew Miller has uploaded a video showing DSD+ running with CubicSDR on OSX. To do this he used a utility called “Wine Skin” which creates a wrapper that allows Windows software to run on a MAC computer running OSX. This means that DSD+ can be run on directly OSX without the need to use a virtual machine with Windows installed on it.
Jupiter and its satellites like Io sometimes interact to create “radio storms” which can be heard from earth at frequencies between 3 to 30 MHz. The radio storms can be predicted and Mario uses the Windows software Radio Jupiter Pro to do this. This helps to predict when are the best times to listen for emissions. On his Raspberry Pi Mario has also written a python script that can do the predictions too.
To make the radio emissions measurements, Mario uses an RTL-SDR dongle and upconverter together with rtl_power to gather FFT frequency power results and waterfall plots. To measure the emissions Mario writes that he keeps the frequency scan running for at least several hours a night with a Raspberry Pi as the receiving computer. For his antenna the low Jupiter frequencies necessitate a large 7 meter dipole tuned for receiving at 20.1 MHz.
For the Internet of Things side of the project, Mario envisions that several amateur radio astronomers around the world could run a similar setup, with all sharing the data to an Amazon AWS data storage server. Mario has already written software that will do the scan and automatically upload the results to the server. To participate you just need to write to him to receive the AWS IoT authentication certificate files.
The internet of things is set to become the next big thing in technology. The IoT consists of multiple networked devices such as sensors and computers connected in various ways such as via wireless communication protocols. LoRa is an abbreviation of “Long Range” and is one such wireless protocol that is being used in IoT devices.
[LoRa] is a radio modulation format that gives longer range than straight FSK modulation. This is achieved by a combination of methods: it uses a spread spectrum technique called Chirp Spread Spectrum (CSS) and it uses forward error coding (in combination with whitening and interleaving).
Over at the RevSpace hackerspace, a hardware hacker called bertrik has been working with his RTL-SDR to try and reverse engineer the LoRa protocol. His goal is to make it so that anyone can receive and decode LoRa signals without needing to purchase specific hardware that supports the modulation. The reverse engineering work is not yet finished, but bertrik has already determined many parts of the protocol by looking at the signals in Audacity. He also writes that there is currently a ready made LoRa decoder available for sdrangelove, a Linux based SDR receiver application similar to GQRX and SDR#.
You might also be interested in this previous article we posted about the Z-Wave wireless networking protocol being hacked with a HackRF.
The two most important things to pay attention to when receiving AERO signals are signal SNR and frequency stability. In order to lock on to the signal, the signal’s frequency must remain relatively stable over a short period of time. For the stability test Jonti writes the following, referencing the image posted below:
You can see the old RTL dongle moves almost 3kHz within a couple minutes after being turned on, this speed is so rapid that JAERO can’t keep up with the frequency changed during this period of time. What’s odd is the old RTL dongle does some fairly crazy stuff around 20 minutes in that lasts for about 15 minutes, JAERO also can’t cope with some of that. The other thing to notice in the old RTL’s spectrograph are vertical lines, these lines I believe are caused by interference entering the dongle between the RTL dongle’s tuner and ADC (analog-to-digital converter).
The frequency stability of the new RTL dongle can only be described as amazing!!! There is not much more than 100 Hz change during the whole test.
The range of frequencies for the SDRPlay is similar to that of the old RTL dongle of about 3kHz. The difference being the transition from the lowest frequency to the highest frequency is slow. Any demodulator should not have any issue tracking this slow and steady change. The only problem you will encounter here is when you are trying to tune into a particular frequency your frequencies will be slightly different depending on the temperature of the SDRPlay.
The results of the frequency stability test on an AERO signal. Left: Standard RTL-SDR; Middle: RTL-SDR Blog Unit; Right: SDRplay.
Jonti also found that in terms of sensitivity the SDRplay was the best at receiving when a non active antenna (an active antenna is an antenna with a built in LNA) was used. The RTL-SDR dongles could not receive well at all when a non active antenna was used. When an active GPS antenna was used the SDRplay was only about 1dB more sensitive than the RTL-SDR dongles.
In his article Jonti expressed concern that the SDRplay did not see much improvement in SNR over the RTL-SDRs when an active antenna was used. Our thoughts on the sensitivity findings are that the SDRplay does not see much improvement with an active antenna because the noise figure of the system is not reduced any further by adding an additional front end LNA (the noise figure in a RF system is almost entirely determined by the first LNA in a RF chain). Adding an extra LNA could even potentially make reception worse by reducing the overall linearity of the system. An external LNA would only be beneficial if a long run of coax was used between the feed and SDR, and in Jonti’s connections he connected the feed and SDRplay with a very short cable. The RTL-SDR only works well with an active antenna because its raw sensitivity at 1.5 GHz isn’t great, and it needs the extra boost from the LNA.
OSX users often don’t have much choice when it comes to general purpose SDR receiver software for the RTL-SDR or other SDR’s. However, one program that works well on Macs is GQRX. Installing GQRX on OSX can sometimes be difficult as the most common installation method involves using Macports, which won’t always work depending on the version of OSX you are using.
Recently, OSX and RTL-SDR user smittix wrote in to use to let us know that there is now a very easy way for El Capitan OSX users to install GQRX. Basically the GQRX team have now released a DMG file which can be downloaded and installed just like most other easy to use applications. Using the DMG file smittix was able to get up and running within 5 minutes.
Every year politicians and business men meet at the “World Economic Forum” in the small mountain town of Davos, Switzerland to discuss various topics and create business deals. This year Quartz, an online newspaper/magazine sent a journalist to the forum. However, the journalist wasn’t tasked with writing a conventional story about the forum topics – instead he was asked to use an RTL-SDR to monitor the private helicopter traffic coming in and out of Davos using ADS-B data. They write that their reasoning for doing this as follows:
We went to all this trouble because there is perennial fascination with the flying habits of the 2,800 Davos delegates. Use of private aircraft, though often wildly overstated, highlights the vast wealth and power that descends upon this small skiing town in the Swiss Alps each year. And their transportation choices are frequently criticized for their environmental impact at a conference that seeks solutions to reducing carbon emissions, among other topics.
Using an RTL-SDR dongle, Raspberry Pi and ADS-B collinear antenna they monitored the flights over Davos. From the data they were able to determine the flight paths that many helicopters took, the types of helicopters used and the most popular flight times. They were able to identify 16 private helicopters that were used, although they write that some may not have had their ADS-B transponders turned on.
The RTL-SDR and various other components used to track the helicopters.The flight path taken by the private helicopters.
AISRec is an RTL-SDR compatible AIS decoder that is made for Windows and Android. AIS is an acronym for Automatic Identification System and is a system used by ships to broadcast position and vessel information. By monitoring AIS transmissions with the RTL-SDR we can build a boat radar system. We have a tutorial on this here (using other software).
The last time we tried AISRec we found that it had very good ability at decoding AIS messages, especially very weak ones and was by far the easiest AIS decoder to set up and use on Windows. The features include:
1. Work with all rtlsdr dongles. Allow future support for other SDR devices. 2. Stable reception of AIS signals at as low as SNR 7 dB. 3. Tolerance to frequency drifts > 30 ppm. 4. Dual-channel reception at 161.975 MHz and 162.025 MHz. 5. Channel selectivity > 56 dB. 6. Low CPU usage. No problem for Atom CPU and above. 7. Output all types of AIS messages (including Class A and Class B) in NMEA formats to UDP ports. 8. Convertion of AIVDM to AIVDO messages for your own ship. 9. Display of the received NMEA messages and the statistics.
The author of AISRec writes in an email to us an explains that the trial version has a time limit and an RX message count limit for each run, whereas the registered lite version will not. The pro version will have some additional features. Currently the author has no method for taking in paid registrations, but plans to have this ready in the future. We will post again once registration is available.
10x NESDR Nano 2+ sets (a.k.a R820T2 w/ TCXO RTL-SDR in small “nano” package)
15x NESDR Nano 2 sets (a.k.a R820T2 RTL-SDR in small “nano” package)
To enter all you need to do is comment on their blog post (not ours!). Their competition runs from 24 January 2016 20:00 UTC to 31 January 2016 20:00 UTC.
