Over on YouTube user Jay Moore has uploaded a video explaining how to connect an RTL-SDR dongle to the IF stage of a hardware radio in order to create a panadapter. In the video Jay briefly explains how a radio with an IF stage works and then shows how he tapped into his Sansui 2000 hardware radio’s IF stage directly from the circuit board. The IF stage then connects to a ham-it-up upconverter which connects to the RTL-SDR.
By connecting the IF stage of a hardware radio to the RTL-SDR it is possible to use the hardware radio as the receiver while using the RTL-SDR to still maintain the benefits of a spectrum display. Most purpose built hardware radios will have better reception than the RTL-SDR.