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GNU Radio and Gqrx SDR Receiver

grc logoIn my last post, I was using the RTL2832 TV tuner dongle to get a simple Software Defined Radio (SDR) operational.  I wanted to use the SDR# program as my receiver but found that the MS Windows tool would not work and so I targeted Gqrx as an alternative. Gqrx is dependent on the GNU Radio.  So in this post, I plan to get Gqrx and GNU Radio up and operational with the RTL-SDR dongle.  I spend some time with other tools to help further verify (with mixed success) that GNU Radio is working.

The contain here comes from multiple source and I attempt to list those sources below.  For a good video to get a sense of what your in for, check out this video. Also, this post covers many of the topics here.

GNU Radio is a free & open-source software development toolkit that provides signal processing blocks to implement software defined radios. It can be used with readily-available low-cost external RF hardware to create software-defined radios, or without hardware in a simulation-like environment. It is being used in hobbyist, academic, and commercial environments to support both wireless communications research and real-world radio systems. 

Gqrx is an experimental AM, FM and Single Side Band (SSB) software defined receiver implemented using GNU Radio and the Qt GUI toolkit. Currently it works on Linux and can use the RTL_SDR dongles as input source.

Also within this post, I venture out from gqrx to examine a few other tools.  I don’t cover much territory, nor have much success.  The insperation to examine these other tools comes mainly from the lengthy post “RTL-SDR and GNU Radio with Realtek RTL2832U [Elonics E4000/Raphael Micro R820T] software defined radio receiver“.  Also check out “Getting Started with GNU Radio and RTL-SDR (on Backtrack)“.

Build GNU Radio on Ubuntu

The GNU Radio web site has specific instructions and a build script for installing it on Ubuntu (I’m using version 13.04).  This process claims it may take 1-2 hours to do the install (for me it ran in 1 hour 14 minutes).  The steps are as follows:

cd ~/src
mkdir ~/gnuradio
cd ~/gnuradio
wget http://www.sbrac.org/files/build-gnuradio && chmod a+x ./build-gnuradio && ./build-gnuradio --verbose

When prompted, tell it to proceed and give it sudo privilege by typing “Y”. Because of the --verbose option, you will see a lot of text whizzing by as the build-gnuradio script does its thing. You’ll also see a percentage complete indicator as the script works its way down it tasks.

The GNU Radio build creates a large variety of tools which get installed into /usr/local/bin.  You also notice that tools not directly related to GNU Radio are also created. I’ll leave it for another time to understand and explain the GNU Radio environment.

The “Hello World” of GNU Radio

To verify that the software is working, best thing is to create the typical “Hello, World” program, just we might have done for our first foray into C++, Python, or other programming language.  In the world of GNU Radio, this program has come to be the phone dial tone. To do this, I followed the video The “Hello World” of GNU Radio: Dial Tone and the gnuradio.org.  I did this using the GNU Radio Companion (executable located at /usr/local/bin/gnuradio-companion).  GNU Radio Companion (GRC) is a graphical tool for creating signal flow graphical models and generating Python source code for the model created.

GRC’s generated flow and code for the “Hello, World” program is listed below. The Python code for the dial tone program was placed in the home directory, and in my case, it was called dail_tone.py. While it can be executed via the gnuradio-companion, it can also be executed via python dial_tone.py. The user interface for the GRC and the corresponding Python code it generated is listed below:

dial_tone.grc - -home-jeff - GNU Radio Companion_006

#!/usr/bin/env python
##################################################
# Gnuradio Python Flow Graph
# Title: Dial Tone
# Author: Jeff Irland
# Description: "Hello, World" program - produces phone dial tone
# Generated: Sat Jun 22 21:24:56 2013
##################################################

from gnuradio import analog
from gnuradio import audio
from gnuradio import blocks
from gnuradio import eng_notation
from gnuradio import gr
from gnuradio import window
from gnuradio.eng_option import eng_option
from gnuradio.gr import firdes
from gnuradio.wxgui import fftsink2
from gnuradio.wxgui import forms
from gnuradio.wxgui import scopesink2
from grc_gnuradio import wxgui as grc_wxgui
from optparse import OptionParser
import wx

class dial_tone(grc_wxgui.top_block_gui):

	def __init__(self):
		grc_wxgui.top_block_gui.__init__(self, title="Dial Tone")
		_icon_path = "/usr/share/icons/hicolor/32x32/apps/gnuradio-grc.png"
		self.SetIcon(wx.Icon(_icon_path, wx.BITMAP_TYPE_ANY))

		##################################################
		# Variables
		##################################################
		self.samp_rate = samp_rate = 32000
		self.noise_slider = noise_slider = .005

		##################################################
		# Blocks
		##################################################
		_noise_slider_sizer = wx.BoxSizer(wx.VERTICAL)
		self._noise_slider_text_box = forms.text_box(
			parent=self.GetWin(),
			sizer=_noise_slider_sizer,
			value=self.noise_slider,
			callback=self.set_noise_slider,
			label='noise_slider',
			converter=forms.float_converter(),
			proportion=0,
		)
		self._noise_slider_slider = forms.slider(
			parent=self.GetWin(),
			sizer=_noise_slider_sizer,
			value=self.noise_slider,
			callback=self.set_noise_slider,
			minimum=0,
			maximum=.1,
			num_steps=1000,
			style=wx.SL_VERTICAL,
			cast=float,
			proportion=1,
		)
		self.Add(_noise_slider_sizer)
		self.wxgui_scopesink2_0 = scopesink2.scope_sink_f(
			self.GetWin(),
			title="Scope Plot",
			sample_rate=samp_rate,
			v_scale=0,
			v_offset=0,
			t_scale=0,
			ac_couple=False,
			xy_mode=False,
			num_inputs=1,
			trig_mode=gr.gr_TRIG_MODE_AUTO,
			y_axis_label="Counts",
		)
		self.Add(self.wxgui_scopesink2_0.win)
		self.wxgui_fftsink2_0 = fftsink2.fft_sink_f(
			self.GetWin(),
			baseband_freq=0,
			y_per_div=10,
			y_divs=10,
			ref_level=0,
			ref_scale=2.0,
			sample_rate=samp_rate,
			fft_size=1024,
			fft_rate=15,
			average=False,
			avg_alpha=None,
			title="FFT Plot",
			peak_hold=False,
		)
		self.Add(self.wxgui_fftsink2_0.win)
		self.blocks_add_xx_0 = blocks.add_vff(1)
		self.audio_sink_0 = audio.sink(32000, "pulse", True)
		self.analog_sig_source_x_1 = analog.sig_source_f(samp_rate, analog.GR_COS_WAVE, 350, .1, 0)
		self.analog_sig_source_x_0 = analog.sig_source_f(samp_rate, analog.GR_COS_WAVE, 440, .1, 0)
		self.analog_noise_source_x_0 = analog.noise_source_f(analog.GR_GAUSSIAN, noise_slider, 0)

		##################################################
		# Connections
		##################################################
		self.connect((self.blocks_add_xx_0, 0), (self.wxgui_scopesink2_0, 0))
		self.connect((self.blocks_add_xx_0, 0), (self.audio_sink_0, 0))
		self.connect((self.analog_sig_source_x_0, 0), (self.blocks_add_xx_0, 2))
		self.connect((self.analog_sig_source_x_1, 0), (self.blocks_add_xx_0, 1))
		self.connect((self.analog_noise_source_x_0, 0), (self.blocks_add_xx_0, 0))
		self.connect((self.blocks_add_xx_0, 0), (self.wxgui_fftsink2_0, 0))

	def get_samp_rate(self):
		return self.samp_rate

	def set_samp_rate(self, samp_rate):
		self.samp_rate = samp_rate
		self.analog_sig_source_x_0.set_sampling_freq(self.samp_rate)
		self.analog_sig_source_x_1.set_sampling_freq(self.samp_rate)
		self.wxgui_fftsink2_0.set_sample_rate(self.samp_rate)
		self.wxgui_scopesink2_0.set_sample_rate(self.samp_rate)

	def get_noise_slider(self):
		return self.noise_slider

	def set_noise_slider(self, noise_slider):
		self.noise_slider = noise_slider
		self.analog_noise_source_x_0.set_amplitude(self.noise_slider)
		self._noise_slider_slider.set_value(self.noise_slider)
		self._noise_slider_text_box.set_value(self.noise_slider)

if __name__ == '__main__':
	parser = OptionParser(option_class=eng_option, usage="%prog: [options]")
	(options, args) = parser.parse_args()
	tb = dial_tone()
	tb.Run(True)

When the GRC flow execution button is pressed, the scope and FFT plots are are created as shown below:

Dial Tone_005

The build for GNU Radio also installs the RTL-SDR software, so it would be wise to test GNU Radio with the RTL_SDR hardware and make sure everything is operating as expected.  I want to make a simple FM receiver, comparable to what was done via rtl_fm in RTL-SDR – Software Defined Radio (SDR) for $20. Something equivalent to:

rtl_fm -W -f 99.5M | play -r 32k -t raw -e signed-integer -b 16 -c 1 -V1 -

Using the following postings as a guide:

I had sufficient success to convince myself that GNU Radio was work.

Building Gqrx on Ubuntu

Gqrx is a software defined AM, FM and SSB software defined radio receiver for RTL-SDR based dongles (as well as the Universal Software Radio Peripherals and Osmo SDR devices).  It features a  Qt GUI.  As a QT program, you’ll need to make sure you have QT4 installed (version 5 will not work) and that you have the qtcreator tool is installed:

sudo apt-get install qt4-default
sudo apt-get install phonon-backend-gstreamer

Now download the source for Gqrx via its page on GitHub  and extract it into your target directory. The posting Getting Started With RTL-SDR and the README on the GitHub site where useful in understanding how to do the install.  I did the following:

cd ~/src
git clone git://github.com/csete/gqrx.git
cd gqrx
qmake gqrx.pro
make

At this point, you should find the gqrx executable in ~/src/gqrx directory.  Start up via ./gqrx and you’ll get the screen below (or set your values to equal this):

Configure I-O devices_001

Click “OK” and the screen below will pop up.  Make sure you have the RTL-SDR dongle plugged in and select the button on the top left to start processing data.  I have tuned the radio to a local FM station at 85.7MHz and listen to Washington Nationals vs. Phillies baseball!

Gqrx 0.0 - rtl=0_004

Building Multimode Radio Receiver

This radio receiver is capable of demodulating muitiple modes, specifically AM, FM, USB, LSB , WFM. TV-FM, PAL-FM. It’s easy to use and  has an automated scanning and spectral zoom features where clicking on the spectrogram or panorama to tune to the frequency of interest.

Multimode documentation is sparse to non existent. The posts “Using the Realtek RTL2832 USB “dongle” as a gnuradio multimode receiver” and “RTL-SDR and GNU Radio with Realtek RTL2832U [Elonics E4000/Raphael Micro R820T] software defined radio receiver” and “Getting Started with GNU Radio and RTL-SDR (on Backtrack)” gave some important hints on how to install multimode and get it operational.  I did the following:

cd ~
svn co https://www.cgran.org/svn/projects/multimode/trunk/ ~/src/multimode
make install

When I executed multimode.py, it didn’t product a display.  I suspect its some subtle Python code problem, or more likely.  incompatibility with the latest GNU Radio libraries.  For now, I’m going to abandon this.

GNU Radio Signal Scanner

gr-scan is a program  built upon GNU Radio, rtl-sdr, and the OsmoSDR Source Block.  This receiver constantly changes frequencies in a set order looking for a frequency that has someone transmitting. It is intended to scan a range of frequencies and print a list of discovered signals.  Installation involved the following steps:

cd ~./src
mkdir gr-scan
cd gr-scan

with your browser, download: http://www.techmeology.co.uk/gr-scan/gr-scan-2012082301.tar.gz
gzip -d gr-scan-2012082301.tar.gz
tar -xvvf gr-scan-2012082301.tar
cd gr-scan-2012082301
make

When I attempted to do the make, it complained about missing Gun Radio files.  I suspect the GNU Radio libraries and include files are layed out differently since the time gr-scan was designed (August of 2012).  I’m leaving fixing this to another time.

What’s Next

In this and the previous SDR posts, I focused on getting a taste of the technology without committing myself to much of an effort.  I really need to study and understand the tools that I have assembled. I still need to do a great deal more studying of  the radio spectrum itself … I feel like I’m wondering in the dark most of the time.

Also, I feel that I’m very limited by the antenna I’m presently using (the pitiful dipole that came with the RTL dongle).  I’m thinking of building a better antenna.  Maybe try to pickup a NOAA weather satellites, with its distinctive audio signal when demodulated, and decode one of its satellite weather photos …. maybe.

Another problem with the RTL-SDR is that its internal oscillator is cheap  and drifts, resulting in clock errors with  many kHz of frequency display error in SDR – depending on a band you’re listening to.  This is very annoying if you use your dongle as a radio scanner – what’s the point of knowing frequency of a transmitter if it’s almost random on your SDR?   This frequency error is linear across the spectrum, and can be adjusted in most SDR programs by entering a PPM (parts per million) offset value.  So I need to calculate this error offset so I can  calibrate the SDR software.

RTL-SDR – Software Defined Radio (SDR) for $20

While researching the GNU Radio project, I came upon references to the RTL2832 TV tuners. These dongle are made to receive and decode the European standard digital television, Digital Video Broadcasting — Terrestrial (DVB-T). (By the way, the North American standard is Advanced Television Systems Committee (ATSC), and not  compatible with DVB-T, so this will not work in North America for TV reception.)  In 2012, Antii Palosaari, discovered that there is a device mode for the Realtek DVB-T device chip (RTL2832U) in which raw samples can be captured and transferred to a host computer. This feature enables this device to be used as an inexpensive “front end”  for a Software Defined Radio (SDR) that could be implemented on a PC or other device.

A SDR provide the ability to sample and record the electromagnetic energy (or radio frequency, called “RF” for short) with no preconceived idea as to the structure of the RF signal.  In a sense, you can interact with the RF signal in its must fundamental form.  In addition, a SDR allows you to implement, by means of software, a radio communication system where components that have been typically implemented in hardware.

SDR solutions for the professional-grade applications and amateur radio have been around for some time, but the appearance of cheap solutions for the hacker is new.  There are general purpose SDR platforms for over $1000, like the Ettus Research Universal Software Radio Peripheral (USRP), the $525 SDR-IQ Receiver, to the $450 bladeRF from the Kickstarter Nuand or Great Scott’s DARPA-Funded HackRF for an estimate $300, and now the $20 hacker grade dongle discussed here.  But unlike most of the other referenced solutions,  the dongle  requires a PC, or some sort of attached processor, to provide the signal processing.

In all SDR solutions, a significant amounts of the signal processing is handed over to a numerical processor, rather than being done in special-purpose RF hardware. Such a design produces a radio which can receive and transmit widely different radio protocols (referred to as a waveform) based solely on the software used.  So in a SDR solution, the electromagnetic waveform is rapidly sampled, the sample values are converted to numerical values, and these numbers are manipulated via a discipline called digital signal processing (DSP).  Ultimately, the resulting DSP numerical values produced are converted to an analog signal that goes to a speaker, TV, or other such output device.

The DVB-T dongles can provide a critical component of a cheap SDR, since the chip allows transferring the raw I/Q samples to the host. What I/Q samples are is well beyond what I wish to describe here, but let it be said that practical hardware design concerns make I/Q data the critical for signal processing.  So the fact the dongle does the digital sampling, called a analog-to-digital converter (ADC), and outputs I/Q samples, makes it a valuable asset for a SDR solution.

So how does one get your PC configured to take the dongles I/Q output and create a SDR?  There is GNU Radio (where this post first begun), but a simpler starting point would be the popular, easy, and open source SDR#.  SDR# can perform the required signal processing in an intuitive user interface (if your into Ham Radio, or bit of a RF hacker, and such).  Unfortunately, I couldn’t get SDR# (a MS Windows application) to operate under  Linux and I had to resorted to some simpler utilities.

The Dongle

All this sounds exciting to me (what a geek!) so I purchased from Amazon one of the dongles, specifically the NooElec TV28T v2 USB DVB-T,  FM+DAB & RTL-SDR Receiver, RTL2832U & R820T Tuner, MCX Input.

71RaTxr2WJL._SL1500_

NooElec TV28T

    • NooElec TV28T – This is the manufacture and model name for the device
    • DVB-T – This device is made to receive and decode the European standard digital television, Digital Video Broadcasting — Terrestrial (DVB-T)
    • FM+DAB & RTL-SDR Receiver – The device can also receive FM radio and Digital Audio Broadcasting (DAB) used in several countries, particularly in Europe. RTLSDR is the popular name give to this class of device, which contain the RTL2832U chip, which can be hacked for SDR use.
    • RTL2832U & R820T Tuner – These are the DVB-T demodulator and TV Tuner chips used in the device.
    •  MCX Input – Is a 3.6 millimeter (0.14 in) micro coaxial (MCX) coaxial RF connector 30% smaller that Sub-Miniature version B (SMB) connectors that are typically used in the USA.  MCX is a standard in Europe. It provides broadband capability from DC to 6 GHz.

From the research I have done, I have found that this dongle provides an approximate tuning range of 25MHz-1700MHz for the SDR.  It has been demonstrated to be compatible with most SDR software, including SDR#.  You can pick up FM radio but  don’t expect to pick up long-wave or AM broadcasts since their spectrum lies below 25MHz. You can listen to the 12m 10m 6m 2m 1.25m 70cm 33cm and 23cm ham band, as well as CB, Marine VHF, RC Band, FRS, GMRS, and Airband (Aviation).

The dongle will not provide the desired SDR function out of the box.  It must first be configured (aka hacked) to stream the I/Q samples to the USB output.  This is where Antii Palosaari’s discovery comes into play.  The wiki’s rtlsdr.org and OsmoSDR are good sources for disparate information concerning RTL2832U based SDR, typically called RTL-SDR.  For my purposes, I wanted to get something initially working on my PC (Linux OS) but ultimately I wanted to have the dongle attached to a Raspberry Pi (RPi) and have the RPi be a server or archive of I/Q samples (sort of a intelligent wide band scanner as done in Raspberry Pi and DVB-T receivers and here Raspberry Pi as Remote Server for RTL2832u SDR and here SDR with Raspberry Pi and DVB-T receivers) that could be processed by my PC.  Therefore, the first step is to get the dongle and a good SDR processor working on my PC.

Building rtl-sdr Library and Capture Tools

The  OsmoSDR wiki has some good instructions on how to build the rtl-sdr software. I basically followed the wiki’s instructions but I had to first install cmake (sudo apt-get install cmake) and libusb (sudo apt-get install libusb-1.0-0-dev) to get a successful make.  I then using the following commands:

cd ~/src
git clone git://git.osmocom.org/rtl-sdr.git
cd rtl-sdr/
mkdir build
cd build
cmake ../
make
sudo make install
sudo ldconfig
cmake ../ -DINSTALL_UDEV_RULES=ON

The result is source code placed in ~/src/rtl-sdr/build/src and the executables are placed in /usr/local/bin: rtl_adsb, rtl_eeprom, rtl_fm, rtl_sdr, rtl_tcp, rtl_test.  The documentation for these utilities is nearly non-existent.  The only documentation I could fine is for the rtl_fm, a posting called Rtl_fm Guide: The long lost documentation.  If you use the command line option --help, you will get some description for each of the tools (see the very end of this post for some screen captures).  Here is a short description and some example usages:

    • rtl_sdr – This is an I/Q recorder for RTL2832 based DVB-T receivers. To send 10 samples to stdout, and sampled at 1.8Ms/s with frequency tuned to 392MHz: rtl_sdr -s1.8e6 -f392e6 -n10 -.
    • rtl_test – Bench-marking tool for RTL2832 based DVB-T receivers.  The -t option only works for Elonics E4000 tuners (Therefore, on non-E4000 tuners, you can not test for the tuning range).  To check the possible tuning range: rtl_test -t.  To check the maximum sample-rate possible on your machine (change the rate down until no sample loss occurs): rtl_test -s 2.5e6
    • rtl_fm – A simple narrow band FM demodulator for RTL2832 based DVB-T receivers.  Rtl_fm is a general purpose analog demodulator. It can handle FM, AM and SSB. It can scan more than a hundred frequencies a second. Make sure rtl_fm and the player are both set to use the same data rate.  Tune into a local FM radio station : rtl_fm -W -f 99.5M | play -r 32k -t raw -e signed-integer -b 16 -c 1 -V1 -
    • rtl_tcp –  An I/Q sample server for RTL2832 based DVB-T receivers.  I/Q samples are streamed to a specified IP address and port.
    • rtl_adsb – A simple Automatic dependent surveillance-broadcast (ADS-B) decoder.  ADS-B is a surveillance technology for tracking aircraft as part of the Next Generation Air Transportation System (NextGen).
    • rtl_eeprom – An EEPROM programming tool for RTL2832 based DVB-T receivers.

First Run of the Dongle

The first thing to do is to plug in the dongle and run the test rtl_test -t.  It gave me an error statement expressing “installing the udev rules file rtl-sdr.rules”.  The site “rtl-sdr on Ubuntu” provides some instructions on how to fix this.  The command lsusb | grep Realtek gives me the information I need to create the following entry into /etc/udev/rules.d:

SUBSYSTEM=="usb", ATTRS{idVendor}=="0bda", ATTRS{idProduct}=="2838", GROUP="adm", MODE="0666", SYMLINK+="rtl_sdr"

After another try, I got a successful test.  Next, I sent ten I/O samples to stdout and then tuned into a local FM radio station using these commands:

rtl_sdr -s1.8e6 -f392e6 -n10 -
rtl_fm -W -f 99.5M | play -r 32k -t raw -e signed-integer -b 16 -c 1 -V1 -

sdrsharp

SDR Sharp

Getting SDR# Running in Linux (didn’t work)

The  rtlsdr.org wiki has some instructions on how to get SDR# working within Linux.  Also, the SDR# home page has a link called One shot install script for Linux. Both these sites require you to build the software from source code. Mono is able to run Microsoft .NET applications in Linux.  I attempted this and got errors that I could not figure out (I’m not a MS Windows developer type and I’m not interested becoming one!).

Given this, I chose a different path. I found another posting that claim to get SDR# running in Linux. In this case, only executable will be loaded, not source code that needs to be compiled. You can download SDR# executable from this posting.  You’ll also need to install mono and PortAudio.  Here is how I did it:

sudo apt-get install mono-complete monodevelop
sudo apt-get install libportaudio2
cd ~/src
mkdir sdrsharp
cd sdrsharp

Within ~/src/sdrsharp, install the downloaded SDR# zip file and unzip it.

cd sdr-nightly
ln -s /usr/local/lib/librtlsdr.so librtlsdr.dll
ln -s /usr/lib/i386-linux-gnu/libportaudio.so.2 libportaudio.so

Note, for the above link, you may need to use locate libportaudio.so.2 to find the PortAudio library.

To test things out, I ran the application using mono sdrsharp.exe and got a core dump.  I attempted this again using the stable version of SDR# instead of the nightly build and got the same results.  After the typical thrashing about, I found a bug report for this problem.  Also see “SDR Software – Good, bad and very ugly“.  Also, there seems to be some sort of dispute between SDR# and a new group calling itself Open SDR#.  I’m not sure, but what appears to be at the heart of this is the level of support of SDR# within Linux.  All this is disappointing since SDR# is a very popular tool and I wish I could find away to make use of it within Linux.

The next logical SDR tool to try would be the Linux-based Gqrx SDR receiver, but in this case, it is dependent on GNU Radio.  I’m attempting to delay my conquest of GNU Radio until I do some experimenting with the dongle.  So lets turn our attention to a much simpler tool.

Getting RTLSDR Scanner Running

RTLSDR Scanner is a simple frequency scanning GUI using the OsmoSDR rtl-sdr library.  I more or less followed the installation instructions but they are confusing/out-of-date and you’ll needed to do some adjustments.  The OsmoSDR rtlsdr library has already been installed earlier in the text, so its not listed here.  To get the required files for RTLSDR Scanner:

sudo apt-get install python python-wxgtk2.8 python-matplotlib python-numpy
cd ~/src
git clone git://github.com/roger-/pyrtlsdr.git
cd pyrtlsdr
sudo setup.py
cd ~/src
git clone git://github.com/EarToEarOak/RTLSDR-Scanner.git

With this, I found I could run ~/src/pyrtlsdr/demo_waterfall.py.  Make sure to read the comments in the file to understand how to change the center frequency, gain, etc.  The image below is demo_waterfall.py tuned to the amateur radio 6 meters band.  The image is called a spectrogram (sometimes call spectral waterfall) is a dynamic, visual representation of the spectrum of frequencies in the RF signal.  Blue is low signal strength, where yellow, and red are higher strengths.

demo_waterfall.py

demo_waterfall.py

To get ~/src/RTLSDR-Scanner/src/rtlsdr_scan.py to work, I had to do some coping of files as shown below:

cp ~/src/pyrtlsdr/rtlsdr/rtlsdr.py  ~/src/RTLSDR-Scanner/src/rtlsdr.py
cp ~/src/pyrtlsdr/rtlsdr/librtlsdr.py  ~/src/RTLSDR-Scanner/src/librtlsdr.py

The image below is from rtlsdr_scan.py, again tuned to the amateur radio 6 meters band.  Here again you see the signal strength of the individual amateur radios as vertical spikes.

rtlsdr_scan.py

rtlsdr_scan.py

So we now have auditory and visual proof the dongle is doing its job. Now its on to GNU Radio!

Command-Line Options for RTLSDR Capture Tools

For reference purposes, below are screen shots of the RTLSDR capture tool’s command line options.

rtl_test -s

rtl_test -s

rtl_test

rtl_test

rtl_tcp

rtl_tcp

rtl_sdr

rtl_sdr

rtl_adsb

rtl_adsb

rtl_fm

rtl_fm

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