March 8, 2015

Building a simple upconverter with a NE612 IC

Upconverters are often used to extend the RTL-SDR dongles minimum receivable range down to the HF, MF and LF bands. They are available for purchase commercially, or you can build your own, which is what Tomasz of mightydevices.com has done.

By using a low cost mixer IC chip called the NE612 and some passive components Tomasz was able to build a low cost upconverter for his RTL-SDR. His upconverter uses a 100 MHz crystal oscillator that brings frequencies between 0-30 MHz up to a range of 100 – 130 MHz, which is in the receivable range of the RTL-SDR. The upconverter circuit was also designed to be able to provide inline power for a active (powered) Miniwhip antenna. Tomasz’s post explains the design choices and theory behind his circuit design.

NE612 RTL SDR Upconverter

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March 8, 2015

New SDR# Plugins: IF Processor & Audio Processor

Over on rtl-sdr.ru, Vaisili the programmer of several popular SDR# plugins has released two new plugins: an IF and an Audio Processor plugin (in Russian, use Google Translate).

The IF Processor plugin is designed to upgrade the Zoom FFT plugin that comes standard with a fresh install of SDR#. The IF processor plugin comes with a tracking notch filter and an asymmetric filter controls. These features will allow you to easily remove interfering signals that appear on top of your signal of interest.

The Audio Processor plugin allows you to improve the audio output using a controllable graphical audio bandpass filter. This feature can help you to remove any hiss or other undesirable sounds in the output audio.

The two new SDR# plugins demonstrated on an AM signal

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March 6, 2015

Using a Quantum Phaser to Null Out Interfering Signals

Over on YouTube user kugellagers has uploaded several videos showing how he used two vertical antennas together with an RTL-SDR and ham-it-up upconverter to demonstrate the effect of using a Quantum Phaser to null out strong interfering signals that can cause trouble when DXing.

A Quantum Phaser is a device that combines signals from two antennas in order to create a steerable null. Essentially this means that a strong nearby station coming from one direction that is overlapping a weak remote station coming from another direction can be heavily attenuated, allowing the weak station to come through.

In his videos kugellagers demonstrates the Quantum Phasers nulling effect with splatter from an AM station, an overlapping IBOC hash signal (AM HD Radio) and Non-Directional Beacons (NDBs).

Phasing Out Splatter From a 50 kW Local On Adjacent Channel

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Phasing Out IBOC Hash From A Strong Local On Adjacent Channel

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Phasing out LF/NDBs With Closely Spaced Vertical Antennas

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March 6, 2015

Installing GQRX on Mac OSX

Mac OSX users can have a hard time with the RTL-SDR as there are not many software packages available for it. One software package that is known to work well on OSX is GQRX, which is a general multi mode receiver GUI that is similar to the Windows software SDR#. Over on smittix’s blog, the author has created a post showing how to install the latest version of GQRX on OSX. The installation involves using Macports, a system that allows some open source programs like GQRX to be automatically compiled and installed on OSX.

GQRX running on a Mac Computer — GQRX running on a OSX Computer

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March 3, 2015

New GUI for rtl_power: QSpectrumAnalyzer

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.

The project can be found at https://github.com/xmikos/qspectrumanalyzer and Mikos is open to pull requests on GitHub.

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March 2, 2015

Decoding Aviation VOR and ILS Signals with RTL-SDR

Previously we’ve posted about how hpux735 (aka William) was able to use an RTL-SDR to decode an aviation VOR navigation signal using GNU Radio and an RTL-SDR. VOR is an acronym for VHF Omni Directional Radio Range and is an older method of navigation used by aircraft.

Now over on YouTube William has uploaded a new video that continues his series on decoding VOR and navigation radio signals. This time he focuses on ILS or Instrument Landing System signals. The ILS is a radio system that is used to help aircraft find and land on the runway safely even in reduced visibility situations such as rain and fog. William’s video explains how ILS works and also shows how he is able to make use of the ILS signal in GNU Radio to extract navigation information.

William has also uploaded some supplemental material to his blog including the GNU Radio grc file and the baseband ILS signal data he collected whilst flying.

VORs and SDRs Part 3: ILS

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February 25, 2015

Linux Command Line based Doppler Correction and Demodulation Tools

Programmer Andres has recently been working on creating a toolset for receiving AX.25 packets (FSK 9600) from satellites with an RTL-SDR or other software defined radio. The AX.25 protocol is commonly used for APRS packet radio or telemetry in amateur radio satellites. Andres’ programs focus on using a true UNIX philosophy of piping data between different programs. The toolset consists of doppler correction and demodulation tools and the piping philosophy is demonstrated in the following example:

rtl_sdr | doppler | demod | multimon-ng

Andres writes…

rtl_sdr receives raw IQ data from satellites which is then piped to “doppler” which corrects doppler offset. Zero centered baseband signal is piped to “demod” which outputs demodulated audio suitable for multimon-ng to do actual AX.25 packet decoding.

Such pipeline is intended for resource constrained embedded platforms like RaspberryPi or BeagleBoneBlack where running full blown SDR software would be too much.

The doppler corrector tool works by using the same libraries for calculating satellite positions as those used in Gpredict and the demod tool uses the liquid-dsp library to demodulate the IQ stream.

More information about Andres’ project can be found in these three blog posts that he has written.

Andres also writes that he would be interested in hearing any feedback or pull requests on GitHub for these tools.

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February 25, 2015

How to Receive the Funcube Satellite with an RTL-SDR

Over on the Hamspirit.de blog author Jan as written a post explaining how to receive the FUNcube satellite with an RTL-SDR dongle (note in German, use Google translate). The FUNcube is a CubeSat (a low cost miniature 10 cm cube sized satellite) which is intended mainly for educating young people about radio, space, physics and electronics, but has also piqued the interest of amateur radio hobbyists.

Jan first writes how the Funcube Dongle was originally invented as a low cost means of receiving the FUNcube satellite, but now there are the even lower cost RTL-SDR dongles. Jan’s post then goes over how to receive the FUNcube at a frequency of 145.935 MHz using software such as SDR-Radio or SDR# and how to decode the telemetry data using the FUNcube dashboard. He also explains a bit about the FUNcubes operating modes which change the satellites transmission strength depending whether or not its solar panels are in sunlight or not.

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