February 9, 2015

New software rtl_heatmap: Web based waterfall plotter for rtl_power

Over on GitHub a new heatmap plotter for rtl_power has been released. The software is called rtl_heatmap and is software that can be used to create a heatmap from the csv data produced by rtl_power. The software creates the heatmap and also adds frequency marker information to the plot. Rtl_heatmap is written in JS and HTML5 and is a web browser based app.

Rtl_power is a tool that can scan a large chunk of bandwidth with an RTL-SDR dongle and record signal power levels over time.

A demo of the software in action can be found at http://heat.wq.lc/.

rtl_heatmap is a web based heatmap plotter for rtl_power

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February 4, 2015

Building a Simple Downconverter for the RTL-SDR

Over on YouTube Adam Alicajic, seller of the LNA4ALL low noise amplifier has uploaded a video showing how to create a simple downconverter using a 1.3 GHz local oscillator and an LNA4ALL. A downconverter extends the frequency range of the RTL-SDR to frequencies higher than the RTL-SDR’s 1.7 GHz limit.

Adam capacitively connects the 1.3 GHz local oscillator to the input of the LNA4ALL, which causes the input signal to be mixed with the input signal from the antenna. This moves a test 2.8 GHz signal down to 1.5 GHz, which is receivable by the RTL-SDR.

DIY poor guy SDR Downconverter

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February 3, 2015

New SDR# RTL-SDR Driver with LNA/Mixer/VGA Gain Settings and Decimation

A new SDR# driver for the RTL-SDR that comes with manual settings for the LNA/Mixer and VGA gain stages as well as software decimation (in Russian use Google Translate) has been released on rtl-sdr.ru. The three seperate gain stages offer much greater control over optimization of signal SNR and interference management. The decimation feature allows you to sacrifice some bandwidth for increased ADC bit resolution. This means that using the decimation feature can significantly improve the SNR of a signal. Update: It turns out that decimation is already used in the existing SDR# code, so using decimation in the new driver won’t improve the real SNR, only the visible SNR – so there will be no audible improvement. It will however allow you to effectively zoom in on the spectrum without loosing visible resolution. Also it allows you to use a higher sample rate (2.8 MSPS) which will improve SNR, whilst maintaining a reasonably sized (small enough) visible bandwidth for narrowband signals.

The driver is based on Oliver Jowet’s modified driver so it should also have the capability to tune down to 13 MHz or lower. To use the plugin simply download the zip file and copy the files into the SDR# folder, replacing all existing files. Previously we posted about another driver with similar capabilities, but this driver was never released to the public. There was also another driver with just the three gain settings released earlier which this driver appears to be based on.

New RTL-SDR Driver with LNA/Mixer/VGA Gain Settings and Software Decimation

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February 3, 2015

Testing the built in IF Filter on the R820T RTL-SDR

As seen in this previous post, the R820T tuner chip used on most RTL-SDR’s has a built in hardware tunable IF filter. Leif, the programmer of the Linrad SDR software has been experimenting with this filter and has uploaded a video of his experiments to YouTube.

In the video he shows how the R820T IF filter can be set to be as narrow as 300 kHz. Using a narrow IF filter can help to reduce the interference from strong nearby stations by up to 30 dB. Leif uses a modified RTL-SDR driver that comes with Linrad which allows the IF filter to be manually modified.

Update: Leif has posted some extra details in the Osmocom mailing list. He writes that the modified driver can be found at https://github.com/dl8aau/librtlsdr and a Windows version is at https://drive.google.com/file/d/0B9m6SAaGpewQeWtyS0lzdW1xVmM/view?usp=sharing.

R820T with IF filtering

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February 3, 2015

Mods and Performance of an R820T2 RTL-SDR

Over on his blog, RTL-SDR experimenter Laidukas had added a post showing how he modded his R820T2 RTL-SDR for improved noise performance. The mods he applies are:

Addition of 100nF, 1nF and 100pF bypass capacitors on the power supply rail.
Added a common mode choke to the 5V line.
Added a MuRata NFM21 EMI suppression filter to the 5V line.
Replaced the oscillator with a 0.3 ppm temperature controlled oscillator (TCXO).
Disabled the internal RTL2832U 1.2V switching supply and provided external 3.3V and 1.2V supplies.
Replaced the MCX connector with an SMA female connector.
Enclosed circuit in a metal box.

In addition to the mods, Laidukas also made some measurements on the performance of the R820T2 on some metrics. In the first test he measured the input insertion loss or SWR. He found that the SWR was below 2 between frequencies of 25 MHz to 1076 MHz. At higher frequencies the SWR reached levels up to about 8.

Another test showed that with the LNA disabled the R820T2 had a lower noise floor by about 7dB, when compared to the R820T.

SWR Plot of the RTL-SDR Antenna Input with LNA disabled

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January 31, 2015

Spying on Keyboard Presses with a Software Defined Radio

Last year Milos Prvulovic, a computer science researcher uploaded some videos to YouTube showing how he was able to remotely and covertly record the keystrokes of a target laptop in another room wirelessly using just a software defined radio, magnetic loop antenna and some custom software.

The target laptop was first modified with special drivers that cause increased and unique memory and processor activity for each key that is pressed. As computers emit unintentional RF emissions, the modified memory and processor activity causes the target laptop to emit a unique RF signature for each key pressed. Milos used this fact to create a program that can detect the RF emissions from the target laptop, and show the key presses made from the target laptop on the spying PC.

EM Covert Channel Attack Setup and Explanation

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EM Covert Channel Attack Through a Wall

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EM Covert Channel Attack from Nearby Desk

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January 29, 2015

Designing a Low Noise UHF Front End with Sharp Filtering for SDR

Most wideband SDR’s do not come with any front-end filtering built in. This limits their ability to receive weak signals in the presence of strong signals. Recently Sivan, a reader of RTL-SDR.com wrote in to let us know about a paper he published through the ARRL detailing how to design a concrete front-end unit for SDR use. A front-end helps to filter out signals that are outside of the desired passband, thus reducing interference from nearby strong signals significantly. Although Sivan uses a USRP with WBX daughtercard in his paper, he writes that the same front-end design principals can be applied to the RTL-SDR as well.

In the paper he designs a 431 – 435 MHz front-end using low cost SAW filters, a low noise amplifier (LNA) and a limiter to protect the radio. He writes that the design could easily be adapted for other bands as well.

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January 29, 2015

SDR# Frequency Scanner Plugin Updated

The popular frequency scanner plugin for SDR# has recently been updated (in Russian, use Google Translate). The frequency scanner plugin allows you to quickly scan through a definable slice of spectrum, stopping to listen on active signals. The new features are outlined below

1. Added the selection of multiple ranges to scan. Ranges can be different modulation and bandwidth scanning step. To select multiple ranges, use Ctrl .

2. The scanner operates completely independently of native squelch SDR #. To determine the end of the activity, a new parameter Hysteresis – is the level below which the signal is considered inactive. When using the option Use Mute , you can disable the squelch SDR #.

3. In setting the added options – choose the scanning signal with the maximum level and the width of the spectrum used.

4. Parameter Detect moved from the window in the panorama scanner settings.

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