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In Howtos Posted by

Nov 13

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RTL-SDR Spectrum Analyzer

Recipe for successfull FPV is good video link, and there is no such with bad antennas. Most of the stock antennas we are getting with the video transmitters and receivers are usually totally out of tune and building your own requires certain tools. One important tool that is frequently mentioned on forums is spectrum analyzer but so far it was too expensive and few have them, but not anymore. Solution is RTL-SDR Spectrum Analyzer.

SDR (software defined radio) hardware is usually too expensive, but thanks to few guys and their discovery that cheap Realtek 2832U tuners actually can receive much more than originaly wanted some of them ranging from 22 to 2200Mhz.

One thing led to another and rtl-sdr project is born. With DVB-T USB dongles priced under $20 its possible to make cheap rtl-sdr spectrum analyzer.

There is wide variety of dongles that could be used, these are the frequently used

Tuner Frequency range
Elonics E4000 52 - 2200 MHz with a gap from 1100 MHz to 1250 MHz (varies)
Rafael Micro R820T 24 - 1766 MHz
Fitipower FC0013 22 - 1100 MHz (FC0013B/C, FC0013G has a separate L-band input)
Fitipower FC0012 22 - 948.6 MHz
FCI FC2580

146 - 308 MHz and 438 - 924 MHz (gap in between)

For the test I'm going to use Rafael Micro R820T bough from ebay seller nooelec but you can also find it from wide variety of sellers including aliexpress.

Since you will most surely want to use other antennas its handy to also get MCX to SMA adapter.

Linux installation instructions

My OS of choice is Linux so thats what I'm going to use in this tutorial. Down below you can find the Windows howto.

Ok, so the package arrived, initial thrill of unpacking is over, usb dongle is plugged in and kernel module dvb-usb-rtl28xxu is automaticaly loaded together with few other modules. Remove the module from kernel together with other dvb modules and add it to the blacklist:

# echo "blacklist dvb-usb-rtl28xxu" > /etc/modprobe.d/rtlsdr.conf

Download the latest rtl-sdr code and build it, instructions can be found here and don't forget to use

# cmake ../ -DINSTALL_UDEV_RULES=ON

Its pretty much done. You have the rtl-sdr installed and luckily running rtl_test will give you something like this:

# rtl_test
Found 1 device(s):
  0:  ezcap USB 2.0 DVB-T/DAB/FM dongle

Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle
Found Rafael Micro R820T tuner
Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6

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...

GNURadio

Most of the software I'm going to use like rtl-sdr spectrum analyzers is actually realying on gnuradio.
We could install it from packages repository of the Linux distribution used but the best method is to get the latest version of the software and install it from source.
Easies way to do this is to run well written build-gnuradio script from gnuradio.org which you can find here. Script will take care of the dependencies too.
More details on the installation from source can be found here.

RTLSDR-Scanner

There are several different software solutions for rtl-sdr spectrum analyzer and one of the simple and good starting point is RTLSDR-Scanner.
Installation instruction together with dependencies can be found on the project page and the result is

Windows installation instruction

  1. SDRSharp is most commonly used software defined radio software for RTL-SDR and thats what we are going to install now. Its available for download on sdrsharp.com downloads page but before that make sure you have .NET redistributable installed since its required by SDRSharp. Now go down the sdrsharp downloads page and download sdr_install.zip.



  2. Extract sdr_install.zip to a folder.

  3. Execute install.bat by clicking it. Its going to open terminal window, download the software, install it and close on finish.


  4. Plug in the dongle and skip the automatic installation of the driver and software. You are going to install this later. This step is important and if you already installed the driver go a head and uninstall it.

  5. Open the sdrshark folder, find the zadig.exe executable and run it as administrator (right click, run as administrator), this is for Windows 7

  6. Once Zadig is started, go to Options and check List all devices.


  7. Now, under device select "Bulk-In, Interface (Interface 0)" and under Driver Target select "WinUSB"


  8. Click "Install Driver" and "Install this driver software anyway" on the pop-up window.


  9. Now close Zadig and execute SDRSharp.exe from the same directory. Near the play button in the top left corner select "RTLSDR / USB" from drop-down menu.


  10. Now click the play button and enjoy the view.
    Here is my LRS UHF.



    This is video transmiter on 1360MHz with untuned receiver antenna.

Android version

There is software for android working with same DVB tuners and can be found here.

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