I have a problem with the "Listen to Aircraft Transponders" section. When I run the rtl_test -t test, I get the following message: Kernel driver is active, or device is claimed by second instance of librtlsdr. In the first case, please either detach or blacklist the kernel module (dvb_usb_rtl28xxu), or enable automatic detaching at compile time.
Can you tell me what this means?
I'm the editor for this book, and I forwarded your question to the authors. Here's how they explained what's going on and how to fix the problem:
The original purpose of the RTL-SDR device was for receiving DVB-T
(worldwide standard for transmitting terrestrial digital video
broadcast). The device that the user is plugging in is supported by
Linux for that purpose, and thus, the default driver loaded by Linux
(dvb_usb_rtl28xxu) drives it as a DVB-T receiver.
This is not what we want when using the hardware as a software
configurable SDR, so we need to tell the Linux kernel never to load that
The obvious solution is to blacklist the troublesome driver:
Assuming you're using raspbian like we show in the book, you should
just add this line to /etc/modprobe.d/raspi-blacklist.conf
You'll need to reboot for the changes to take effect, but then things should work as you expect.
I hope this helps answer your question and helps you run the hack in the book.
Senior Editor, O'Reilly Media