A new instructional page for the rtl_power tool is now available on main author keenerds webpage. Rtl_power is a command line tool for logging wide band frequency power scans to a CSV file. The CSV files can then be used for analysis or to create a large frequency plot image. An example of a 2 GHz+ bandwidth scan over 24 hours is shown below. Rtl_power is available as part of the official osmocom RTL-SDR drivers.
Amateur radio astronomy hobbyist Jim Sky has written on his blog about his new program called RTL Bridge with allows the RTL-SDR to directly connect to his other radio astronomy programs Radio-SkyPipe and Radio-Sky Spectrograph. Jim describes his two existing program as follows.
Radio-Sky Spectrograph displays a waterfall spectrum. It is not so different from other programs that produce these displays except that it saves the spectra at a manageable data rate and provides channel widths that are consistent with many natural radio signal bandwidths. For terrestrial , solar flare, Jupiter decametric, or emission/absorption observations you might want to use RSS.
Radio-SkyPipe is a souped-up strip chart program which plots signal strength over time. When getting its data from RTL Bridge, RSP is plotting the total power in the spectrum covered by the RTL receiver centered around its set frequency. While the raw values are proportional to power, you will have to apply a function via the RSP Equations feature to apply a calibration if you want absolute values. For signals that do not have significant spectral structure of interest, this would be the preferred way to plot the data.
Over on ttrftech’s blog in Japanese (use Google translate), ttrftech has uploaded a new RTL-SDR program for Chrome which allows 3D visualization of the frequency spectrum. The program can be installed by simply downloading the files from GitHub and loading them into Chrome. Ttrftech explains that the program should work on any OS, but he has so far only been able to test it on MacOS.
Hackaday has brought to attention a document written by a Rory O’Hare which discusses the journey Rory took in trying a decode an unknown 433 MHz signal received from his SDR dongle.
If you are interested in manually decoding some unknown signals you may be interested in this write up as it discusses his entire journey including the failures he encountered along the way. Basically he records some packets using his SDR dongle, works out their bit patterns manually and then attempts to find correlations between the packets in an attempt to discover their structure. In the end his efforts are successful as he discovers that he is receiving a temperature sensor and is able to decode the temperature readings.
Over on YouTube user John Miller has uploaded a video showing an example of DSD+ decoding an NXDN96 voice signal. NXDN is a digital voice protocol by developed by Kenwood that is often used by public safety organizations.
John uses SDR# to receive the NXDN signal and then pipes the audio to DSD+ using Virtual Audio Cable for decoding.
Over on YouTube user Guilherme Dattoli Cirigliano Cortes has uploaded a video showing his use of the RTL-SDR in some MATLAB based cognitive radio experiments. Cognitive radio is a upcoming technology which aims to increase radio spectrum use efficiency by finding and using the intermittent periods of unoccupied frequency space.
The uploader explains his task below.
The fundamental task of each Cognitive Radio (CR) user in CR networks, in the most primitive sense is to detect the licenced users, also known as primary users, if they are present and identify the available spectrum if they are absent. This is usually achieved by sensing the RF environment, a process called spectrum sensing. Here we use one of the technique of spectrum sensing called energy detection.
Amateur radio astronomer Y1PWE has uploaded a pdf document describing how he created a low cost hydrogen line telescope using an RTL-SDR dongle (links under heading 2. H-Line Receiver) . 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, a power spike indicating the hydrogen line can be observed in a frequency spectrum plot.
Y1PWE created a radio telescope using a quad 22 element yagi antenna, several LNA's and filters and an RTL-SDR dongle and laptop. Using this setup he can capture some raw IQ data from the RTL-SDR and then use an FFT averaging program to produce some plots. In his plots the hydrogen line is clearly visible.
 |
 |
Over on YouTube user crookedninja5 has uploaded a video showing what he calls the “Easy HF dongle mod”. The mod involves soldering a wire from Pin 1 on the RTL2832U chip to the static protection diode near the antenna input. At the same time he also uses the modified RTL-SDR dll file for SDR# which enables the “no hardware mod” direct sampling mode.
Using this mod he is able to get decent coverage of 0 – 14.4 MHz.
