Tagged: rtl2832u

RTL-SDR Tutorial: Measuring filter characteristics and antenna VSWR with an RTL-SDR and noise source

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.

These tutorials are based heavily on information learned from Adam Alicajic's (9A4QV), videos which can be found at [1], [2], [3], [4]. Adam is the creator of the LNA4ALL and several other RTL-SDR compatible products. Recently Tim Havens also posted some experiments with characterizing home made filters on his blog.

Characterizing Filters

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:

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.

The BG7TBL Noise Source
The BG7TBL Noise Source

If you have a ham-it-up upconverter and are good at soldering small surface mount components you might instead consider purchasing the noise source kit add on. Here is a video showing how to build and test the ham-it-up noise source. Continue reading →

RTL-SDR Tests: R820T vs R820T2 Stability Tests for Radio Astronomy

Amateur Radio astronomer Peter Kalberla recently wrote in to let us know about a paper he has written exploring stability issues and comparing the R820T and R820T2 RTL-SDR tuner chips (pdf warning). The R820T2 tuner is an upgrade to the R820T tuner which is used in the most commonly found RTL-SDR dongles.

Peters first results show that the R820T2 has better reception and less spurious features at frequencies above about 1.45 GHz and improved frequency stability (with the newer R820T2 dongles that use the SMD oscillator). His second set of results explore issues that are more closely relevant to radio astronomy including observed spectra, Allan variance (frequency stability) tests and determining the shape of the R820T/2 internal bandpass filter.

In the conclusion of the paper Peter writes:

Two Newsky RTL2838U dongles were tested, the R820T2 device against the R820T. The evaluation results in a clear preference for the new RTL2838U/R820T2 dongle. In the L-band the new dongle is at least 2.7 dB more sensitive. According to the radiometer equation the effective system temperature is reduced by almost 50%. Most important for reliable radio astronomical observations are stability issues. Allan variance tests have shown that the R820T2 dongle is far better then the older version. The stability is comparable to that of professional radio astronomical devices. The tests have shown that using the full bandwidth of the RTL-SDR devices results in spurious baseline ripples. For a good performance it is recommended to use the dongles at reduced bandwidth. rtl power with the crop option -c 0.5 appears to be a good choice.

Broad band performance of the R820T dongle (top) and R820T2 (bottom)
Broad band performance of the R820T dongle (top) and R820T2 (bottom)

Capturing Noise Bursts from Jupiter with an RTL-SDR

Recently amateur radio astronomer Jim Brown used an RTL-SDR dongle together with a Ham-it-up upconverter and preamp to capture noise bursts from the planet Jupiter. Not much information about his observations are available yet as he has not yet made a write up, but he has given the image of the noise burst shown below to Jim Sky, programmer of RTL Bridge and Radio-Sky Spectograph which is some of the software used to capture the noise bursts. We will make another post in the future if Jim Brown does a write up.

Jim Sky has also updated his RTL Bridge software to use Oliver Jowetts patched drivers, which allow the RTL-SDR to receive below its usual 24 MHz limit.

Noise burst from Jupiter captured with an RTL-SDR
Noise burst from Jupiter captured with an RTL-SDR

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.

An NE612 based upconverter
An NE612 based upconverter
NE612 RTL SDR Upconverter

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
The two new SDR# plugins demonstrated on an AM signal

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

Phasing Out IBOC Hash From A Strong Local On Adjacent Channel

Phasing out LF/NDBs With Closely Spaced Vertical Antennas

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

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.

QSpectrumAnalyzer GUI for rtl_power
QSpectrumAnalyzer GUI for rtl_power