The rtlizer: low-cost spectrum analyzer using RTL2832U SDR

The Equalizer: 1985 TV Series

"Got a problem? Odds against you? Call the Equalizer. 212 555 4200." - The Equalizer

A spectrum analyzer is a serious piece of kit for an electronics engineer. You can easily spend over RM10,000 on one, although you can get generic ones online for RM4000. The RTL2832U DVB-T USB dongle SDR can be used to make a basic spectrum analyzer for RM39.

It is the great equalizer (after the 1985 TV Series), leveling the playing field for students, hobbyists and Third World engineers.

OZ9AEC has made an everyman's spectrum analyzer using a Raspberry Pi and the RTL2832U dongle. Happily, his design runs without modification on my Slackware 14.2 laptop.

rtlizer required rtl-sdr, which I had previously installed. Here we just need to tell rtlizer where to find it:

$export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/lib/pkgconfig

And add '/usr/local/lib' to the file /etc/ld.so.conf. If you had just installed rtl-sdr it helps to also do:

$ldconfig

I downloaded rtlizer, and built it thus:

$unzip rtlizer-master.zip
$rtlizer/rtlizer-master/src$make

If necessary, unload (or even better, blacklist) the dongle's kernel drier:

$modprobe -vr dvb_usb_rtl28xxu

rmmod dvb_usb_rtl28xxu

rmmod dvb_usb_v2

rmmod rc_core

And it runs, right out of the box (with a complaint or two):

$./rtlizer 1024x720

(rtlizer:22436): Gtk-WARNING **: gtk_window_parse_geometry() called on a window w

ith no visible children; the window should be set up before gtk_window_parse_geom

etry() is called.

window size: 1024x720 pixels

SCALE: 7.20 / Y0: 216 / TXTMARG: 21

Found Fitipower FC0012 tuner

rtlizer responds to the the arrow keys. And wneh I centered rtlyzer on 330MHz, my autogate remote's frequency, I got the spike in the center, with the upper and lower sidebands when the button was pressed:

rtlizer centered on 330MHz

There you have it: an RM39 spectrum analyzer, courtesy of OZ9AEC. Happy Trails.

Software Defined Radio: installing rtl-sdr in Slackware 14.2

RTL2832U 

I got a generic no-name RTL2832U TVB-T USB dongle for just RM39. Plug it into a Slackware 14.2 with a recent kernel (I have 4.16.0) and if you did a 'dmesg -T':

[Fri Mar 30 00:12:58 2018] usb 1-2: new high-speed USB device number 57 using xhci_hcd
[Fri Mar 30 00:12:58 2018] usb 1-2: New USB device found, idVendor=0bda, idProduct=2838
[Fri Mar 30 00:12:58 2018] usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[Fri Mar 30 00:12:58 2018] usb 1-2: Product: RTL2838UHIDIR
[Fri Mar 30 00:12:58 2018] usb 1-2: Manufacturer: Realtek
[Fri Mar 30 00:12:58 2018] usb 1-2: SerialNumber: 00000001
[Fri Mar 30 00:12:59 2018] usb 1-2: dvb_usb_v2: found a 'Realtek RTL2832U reference design' in warm state
[Fri Mar 30 00:12:59 2018] usb 1-2: dvb_usb_v2: will pass the complete MPEG2 transport stream to the software demuxer
[Fri Mar 30 00:12:59 2018] dvbdev: DVB: registering new adapter (Realtek RTL2832U
 reference design)
[Fri Mar 30 00:12:59 2018] i2c i2c-11: Added multiplexed i2c bus 12
[Fri Mar 30 00:12:59 2018] rtl2832 11-0010: Realtek RTL2832 successfully attached
[Fri Mar 30 00:12:59 2018] usb 1-2: DVB: registering adapter 0 frontend 0 (Realtek RTL2832 (DVB-T))...
[Fri Mar 30 00:12:59 2018] i2c i2c-12: fc0012: Fitipower FC0012 successfully identified
[Fri Mar 30 00:12:59 2018] lirc_dev: IR Remote Control driver registered, major 237
[Fri Mar 30 00:12:59 2018] IR LIRC bridge handler initialized
[Fri Mar 30 00:12:59 2018] Registered IR keymap rc-empty
[Fri Mar 30 00:12:59 2018] rc rc0: Realtek RTL2832U reference design as /devices/
pci0000:00/0000:00:14.0/usb1/1-2/rc/rc0
[Fri Mar 30 00:12:59 2018] input: Realtek RTL2832U reference design as /devices/p
ci0000:00/0000:00:14.0/usb1/1-2/rc/rc0/input132
[Fri Mar 30 00:12:59 2018] rc rc0: lirc_dev: driver ir-lirc-codec (dvb_usb_rtl28xxu) registered at minor = 0
[Fri Mar 30 00:12:59 2018] usb 1-2: dvb_usb_v2: schedule remote query interval to
 200 msecs
[Fri Mar 30 00:13:00 2018] usb 1-2: dvb_usb_v2: 'Realtek RTL2832U reference design' successfully initialized and connected
[Fri Mar 30 00:13:00 2018] usbcore: registered new interface driver dvb_usb_rtl28xxu

            This means the device is working and ahs been recognized by the kernel:
root$ls -lt /dev/dvb
total 0
drwxr-xr-x 2 root root 120 Apr  2 09:33 adapter0

The SDR software of choice for Linux Slackware 14.2 has got to be rtl-sdr. I simply followed the steps for Linux listed in their 'Quick Start Guiide', and are relisted here as tested steps for Slackware 14.2.

My download was from osmocom.

~/sdr/rtl-sdr$unzip rtl-sdr-master.zip

~/sdr/rtl-sdr/rtl-sdr-master$autoreconf -i

~/sdr/rtl-sdr/rtl-sdr-master$./configure

~/sdr/rtl-sdr/rtl-sdr-master$make

~/sdr/rtl-sdr/rtl-sdr-master$su -c "make install"

Since rtl-sdr is mainly a library; at this point it will list some instructions on linking to it:

----------------------------------------------------------------------

Libraries have been installed in:

   /usr/local/lib

If you ever happen to want to link against installed libraries

in a given directory, LIBDIR, you must either use libtool, and

specify the full pathname of the library, or use the '-LLIBDIR'

flag during linking and do at least one of the following:

   - add LIBDIR to the 'LD_LIBRARY_PATH' environment variable

     during execution

   - add LIBDIR to the 'LD_RUN_PATH' environment variable

     during linking

   - use the '-Wl,-rpath -Wl,LIBDIR' linker flag

   - have your system administrator add LIBDIR to '/etc/ld.so.conf'

See any operating system documentation about shared libraries for

more information, such as the ld(1) and ld.so(8) manual pages.

----------------------------------------------------------------------

~/sdr/rtl-sdr/rtl-sdr-master$su -c "ldconfig"

Now you will need to remove (or better yet blacklist) the kernel driver for RTL2832U:

root@aspireF15:/home/heong/sdr$modprobe -vr dvb_usb_rtl28xxu

rmmod dvb_usb_rtl28xxu

rmmod dvb_usb_v2

rmmod rc_core

A quick test (Ctrl-C to exit):

$rtl_test

Found 1 device(s):

  0:  Realtek, RTL2838UHIDIR, SN: 00000001

Using device 0: Generic RTL2832U OEM

Found Fitipower FC0012 tuner

Supported gain values (5): -9.9 -4.0 7.1 17.9 19.2

Sampling at 2048000 S/s.

Info: This tool will continuously read from the device, and report if

samples get lost. If you observe no further output, everything is fine.

Reading samples in async mode...

Signal caught, exiting!

^CSignal caught, exiting!

User cancel, exiting...

Samples per million lost (minimum): 0

The next command to use is rtl_power. Aim it at some known frequency, perhaps your local FM radio station. In my case it aimed it at my autogate remote at 330MHz:

$rtl_power -f 320000000:340000000:1000 -e 10m -g 40 -i 1s persona.csv

Number of frequency hops: 8

Dongle bandwidth: 2500000Hz

Downsampling by: 1x

Cropping by: 0.00%

Total FFT bins: 32768

Logged FFT bins: 32768

FFT bin size: 610.35Hz

Buffer size: 16384 bytes (3.28ms)

Reporting every 1 seconds

Found 1 device(s):

  0:  Realtek, RTL2838UHIDIR, SN: 00000001

Using device 0: Generic RTL2832U OEM

Found Fitipower FC0012 tuner

Tuner gain set to 19.20 dB.

Exact sample rate is: 2500000.107620 Hz

User cancel, exiting...

This produces a massive data file persona.csv.

Now we need to visualize the data. keenerd has a simple python script, heatmap.py. Download it, rename it to heatmap.py and make it executable:

$chmod +x heatmap.py

We aim it at persona.csv:

$./heatmap.py --offset 1000 --ytick 0.001s --palette charolastra persona.csv persona.png

The output is an image file persona.png, which looked something like this:

x-axis is frequence, y-axis is time. The 8 red smudges correspond to two buttons on the autogate remote, 4 presses each

There you have it: instant gratification SDR. 

Happy Trails.

Software Radio Ga Ga

Philips transistor radio, circa 1970

"I'd sit alone and watch your light
My only friend through teenage nights
And everything I had to know
I heard it on my radio ...

You had your time, you had the power
You've yet to have your finest hour
Radio, radio" - Queen, Radio Ga Ga 

Back in 1974, Mum bought a transistor radio, and it was a technical marvel. Older radios used vacuum tubes, took minutes to warm up, failed often and were the size of a coffee table. The new radio lasted over 10 years despite being knocked off the mantelpiece more than once.

Eventually I learned in Uni this marvel is of a new superheterodyne design. And such a satisfying word it was- it rolls off your tongue guaranteed to impress those 1960s era dinosaurs still clinging to their relay logic computers.

Transistor Radio

  

Superheterodyne receiver

Radio signal at various stages

Then in 1992 there was this incredible IEEE paper "Software Radio: Survey, Critical Analysis and Future Directions" by Joe Mitola, describing a radio largely implemented in software, a Software Defined Radio, and everything changed again.

Software allowed the audio signal to be digitally encrypted; security is now much stronger. The military was an enthusiastic early adopter. It was also more resistant to jamming, used its radio spectrum much more efficiently, and more than one radio protocol can be supported. This was a great boon to cellphones, especially the base stations. 

But SDR was not really my specialty - it was far removed from the superheterodyne of yore, and so for the next 20 years SDR remained an exotic technical curiosity, extolled in the IEEE. 

In 1998 Digital Terrestrial Television DVB-T started replacing regular analog TV worldwide. Realtek, a Taiwan IC maker introduced the RTL2832U, and IC meant for DVB-T. In 2010 Eric Fry, while writing a Linux driver for the RTL2832U discovered that it was possible to read raw I/Q data from it. This meant the RTL2832U-based TVB-T USB dongle can be used as a cheap general-purpose SDR. 

The RM39 RTL2832-based TVB-T USB Dongle au naturel

And everything changed again. Like the superheterodyne, SDR is suddenly within reach.

In the next few posts I shall show how to install SDR software for Slackware 14.2. Some of the uses for SDR are a low-cost spectrum analyzer, lightning detector and autogate remote hacker. All far better things to do than watching TV with it. 

Life is good- Happy trails.