FAQ RTL SDR

Help and Support

I get a -3 error when using an RTL dongle.

usb_open error -3
Please fix the device permissions, e.g. by installing the udev rules file rtl-sdr.rules
Failed to open rtlsdr device #0.

If you are getting the above error, like I was on the ASUS Tinkerboard, you can fix this by running the following.

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

This installs the rtl-sdr.rules file from the Osmocom RTL-SDR source code into your system. It's a fairly quick install and always fixes the underlying problem. Plus you get the updated RTL packages direct from source, so that's a nice bonus.

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On the Raspberry Pi 4 I get -7 errors

If you're getting the following ...

Found 2 device(s):
  0:  MimoCAD, MimoSDR, SN: 000005410
  1:  MimoCAD, MimoSDR, SN: 000005411

Using device 0: Generic RTL2832U OEM
Detached kernel driver
rtlsdr_read_reg failed with -7
rtlsdr_write_reg failed with -7
rtlsdr_read_reg failed with -7
rtlsdr_write_reg failed with -7

The fix for this is to upgrade the firmware. That will get around the heat issue with the release firmware on the Raspberry Pi 4 as well as fixing the quirk of the VLI VL805 PCIe to USB controller where the RTL dongles (Of the RTL2838U type) return a -7 error.

• sudo apt update
• sudo apt upgrade
• sudo apt install rpi-update
• sudo apt dist-upgrade
• sudo rpi-update
  • When asked press y to confirm you wish to update the firmware and press Enter.

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RPI Swap File

Follow this link to set up a swap file when running the make command. You do not need to edit the fstab as you only need the swap during the software development stage.

https://www.tecmint.com/create-a-linux-swap-file/

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RPI4 ffmpeg

I used this to setup ffmpeg for RPI4 - https://gist.github.com/jjangsangy/058456fe2d04e3c5f6107d62b60542e3