Few weeks ago I stumbled upon some topic on one of FPV forums about checking frequency, spectrum, antennas etc. I realized that people are using cheap DVB-T tuner based on Realtek RTL2832U chip as spectrum analyzer, SDR (software defined radio) and even as osciloscope.
There were many situations in my hobby when this brilliant device could help a lot. This discovery was so hot, so I decided to buy such usb dongle ASAP, even at slightly bigger price (55zł ~ $16) than directly from China. I found it in one shop in my town and next day I became happy owner of this tuner
It’s equipped with a little different tuner than described on rtlsdr/osmocomSDR site, Fitipower FC0013 capable of working within 22-1100MHz frequency range:
To be clear: I use Linux
First step was to download and install rtl-sdr library from http://sdr.osmocom.org/trac/wiki/rtl-sdr . In this package there are also ready made udev rules to install, so root access is not required later for using it.
On this web page one can find also links to some related projects using this library.
Next step was to get pyrtlsdr library for Python as most of these project are written in that language. After installation of few more dependencies as wxPython, numpy, matplotlib etc I started testing software
My first application was RTLSDR-Scanner. Kind of old school, well known spectrum analyzer:
Easy to operate, with zoom but capable to scan only within range of whole MHz, so scan in narrower range than 1MHz is not possible (you could zoom, but it doesn’t enhance frequency resolution).
So, it was quite good, but I needed more
Waterfall applications is a real power of computerized spectrum analyzer!
This very easy Python script is more than useful.
You could select and measure frequency range, make pan and zoom (but on lower frequencies application crash during zooming), change sesnsitivity of tuner to remove clipping and additional strips caused by this.
Yes, you are reading right: Audacity – well known audio editing program. I made a little patch (not perfect) to allow change sample rate up to 10MHz because default maximum was 100kHz and typical rtl-sdr sample rate is about 2MHz, so selection tool and fft features are not working correctly.
Using rtl_sdr utility from rtl-sdr library, I dumped raw samples near desired frequency and then I imported it as raw 8 bit stereo samples into Audacity. Below are results:-)
- this is 5 channels radio (6 peaks of synchronization pulses)
- main frequency is shifted by about 5kHz from sampling base i.e. channel frequency – and it’s cause of poor reception
- deviation is about 3kHz (to about 8kHz from center of channel)
Very tempting looks SDR# (available also on Windows) but require a lot more weird dependencies, so I put it for later.
But I’m sure that this topic will return some day with more new cool informations
Update 2013.06.22: second part is here.