OpenWRT is a special custom Linux based firmware designed to create a fully functional Linux system on a internet router by replacing the stock firmware. Since OpenWRT is Linux based, it is possible to install the RTL-SDR software and run it on the router itself. On his blog Tom Jones has posted a brief tutorial showing how he got the RTL-SDR working on a WR703N router that is running OpenWRT. Basically he just installs the RTL-SDR package which is available through the OpenWRT package manager and runs rtl_tcp, but he talks about a few adjustments he had to make to the rtl_tcp buffers to make it run smoothly. The WR703N is a mini wireless router that goes for about $30 USD on Amazon.
We also looked around for more information about running RTL-SDR on OpenWRT and found this older post from Yuval Adams showing how he got dump1090 and the flightradar24.com feeder running also on an OpenWRT’d WR703N router.