Android app programmer Nikos recently wrote in to let us know about his new app called “Track your flight Europe”. His app can be used together with an RTL-SDR and USB OTG cable to track aircraft via ADS-B. The difference between Nikos’ app and other similar ADS-B apps is that his app is specifically designed for tracking the aircraft you are flying in by providing an offline map which does not require an internet connection to display.
By using an RTL-SDR dongle together with a low cost noise source it is possible to measure the response of an RF filter. Also, with an additional piece of hardware called a directional coupler the standing wave ratio (SWR) of antennas can also be measured. Measuring the response of a filter can be very useful for those designing their own, or for those who just want to check the performance and characteristics of a filter they have purchased. The SWR of an antenna determines where the antenna is resonant and is important for tuning it for the frequency you are interested in listening to.
Using just a noise source and RTL-SDR dongle it is possible to determine the properties of an RF filter. In our experiments we used the following equipment:
The BG7TBL noise source is a wideband noise source that can provide strong noise over the entire frequency range of the RTL-SDR. It requires power from a 12V source which can be obtained from a common plug in power supply. It also uses an SMA female connector, so you may need some adapters to connect it to your filter under test (adapters can be found cheaply on Ebay). Finally a quick warning: be careful when handling the circuit board after it has been powered for some time as some of the components can get very hot. Note that if the Ebay store runs out of these there is also a seller on Aliexpress with some available, just type "noise source" in the search bar.
A new GUI for rtl_power has been released by programmer Mikos. Although there are already several rtl_power GUIs and spectrum analyser applications that exist, Mikos developed QSpectrumAnalyzer because he found that the alternatives were either slow, closed source or Windows only.
Rtl_power is a command line tool that can be used with an RTL-SDR to create a spectrum scan of a large swath of bandwidth that is greater than the RTL-SDRs maximum sample rate.
Happysat, a reader of RTL-SDR.com has written in to remind us that the International Space Station (ISS) is currently transmitting slow scan television (SSTV) images out of respect of the 80th birthday of Russian cosmonaut and first man to go to space Yuri Gagarin. The images will be transmitted continuously until 24 February 21.30 UTC.
SSTV is a type of radio protocol that is used to transmit low resolution images over radio. A RTL-SDR dongle and satellite antenna (QFH, turnstile, even terrestrial antennas like random wire antennas and monopoles have been reported to work) can be used to receive and decode these images. Happysat writes that it is expected that the ISS will continuously transmit 12 images at a frequency of 145.800 MHz FM using the SSTV mode PD180, with 3 minute off periods between each image.
In a previous post we talked about the SatNOGS project which aims to provide low cost satellite ground stations (where one critical component is currently an RTL-SDR dongle) along with free networking software in order to create a crowd sourced satellite coverage network. The SatNOGS project was also recently the grand prize winner of the Hackaday prize which saw them take almost $200k US dollars of prize money.
The new versions fixes some minor errors, brings back their ‘spectrum viewer’ software and also comes with a ‘DAB mini’ receiver which is simply a smaller windowed version of the regular DAB receiver. The new version also now supports the sdrplay and Airspy software defined radios.
The goal of Ilias’ project was to be able to use the RTL-SDR and MATLAB to uncover the details of a 433 MHz transmitter he bought on Ebay. He wanted to see if he could determine the protocol and recover the data before even looking at the transmitter’s library code.
To do this he first used SDR# to record the data sent at 433 MHz. Then by looking at the waveform in the Audacity audio editor he was able to determine that the signal was on-off-key (OOK) modulated and from this knowledge he was able to manually recover the binary string. Next he used MATLAB to create a program that can automatically decode the received OOK signal. His post goes into further detail about the signal processing steps he took in MATLAB.
Earlier this year the successor to the hugely popular Raspberry Pi, the Raspberry Pi 2 was released. The Raspberry Pi 2 is a mini embedded computer that can run Linux.
Over on the RS Design Spark website Andrew Back has posted a tutorial showing how he installed GNU Radio and RTL-SDR on the Raspberry Pi 2. He also shows that the Raspberry Pi 2 runs the CPU intensive GNU Radio software well, utilizing 70% CPU when running osmocom_fft, a GNU Radio based spectrum analyzer. Andrew also installs and tests the gr-air-modes GNU Radio program which is an ADS-B receiver, finding that it also performed well with low CPU utilization.
