For people already with expensive ham radios, the RTL-SDR can be used as a cheap panadapter. A panadapter is device that allows you to visually see the RF spectrum and waterfall being received by the ham radio. There are multiple (expensive) commercial panadapters available, but combined with a PC or laptop, the RTL-SDR will work just as well.
In this video YouTube user akdude47 shows a tutorial on setting up the RTL-SDR as a panadapter for a Yaesu FT-857. The setup involves connecting the IF output of the radio to the RTL-SDR, and putting in some settings into HDSDR.
How to setup a RTL SDR with HDSDR and a FT-857 for a panadapter and second receiver.
Over on the Radio Antics blog fellow RTL-SDR enthusiast Andrew has been using the RTL-SDR to receive Slow Scan Television (SSTV) amateur signals. SSTV is a method ham radio enthusiasts use to send small images to one another. The images often contain their ham call sign overlaid on the image.
Andrew was able to receive several SSTV images using an R820T dongle tuned to the 27 MHz (11 meter) band. He also used a Funcube Dongle+ and got similar results.
Check out his post for some of the images he received, and his video below for an example of the receiving process.
YouTube user opilarczyk has posted a video comparing HF performance of the rtl-sdr with the direct sampling mod at 7MHz with WebSDR, an online SDR streaming site. The comparison shows how the direct sampling mod is extremely susceptible to broadcast FM interference.
RTL-SDR gqrx direct sampling vs WebSDR on rtl2832u
Digital Radio Monodial (DRM) radio is a type of digital shortwave radio signal that is used by international shortwave radio broadcasters. It provides superior audio quality compared to AM signals by using digital audio encoding. With an upconverter, good antenna, and decoding software the RTL-SDR software defined radio can receive and decode DRM signals. This tutorial is also applicable to other software defined radios that can receive HF with or without an upconverter, such as the HackRF, Airspy, Softrock and Funcube dongle.
Examples of DRM Decoding
YouTube user Superphish shows DRM reception with his Ham-it-up upconverter, and rtl-sdr.
DRM REE Noblejas Radio with RTL SDR (RTL2832), Nooelec Ham It Up Upconverter, SDR Sharp and DREAM
The RTL-SDR software defined radio can be told to run in a mode called "direct sampling mode", which with a small hardware mod allows the dongle to tune to the HF frequencies where ham radio and many other interesting signals are found. This means that no upconverter circuit is required.
However, the difficulty with direct sampling is that a hardware modification to the dongle is required. Also, the performance can not be expected to be as good as an upconverter without the addition of extra filtering circuits. RTL-SDR Blog V3 Note: Note that our RTL-SDR Blog V3 already has the direct samping mod done and built in, so no hardware modifications are required for those units! Just see the V3 users guide for information on activating direct sampling mode.
The direct sampling mode was originally discovered and discussed in this Google groups thread.
YouTube user Superphish was able to receive HF AM broadcast radio, and a decode a HF weather fax signal at 5.8MHz using the direct sampling mod.
HF AM Radio with RTL SDR (RTL2832) in Direct Sampling Mode with SDR Sharp
Upconverters give the rtl-sdr the ability to receive frequencies below it’s minimum frequency. This allows reception of things like AM broadcasts, ham radio signals, weatherfax, international radio and much more.
There are dozens of upconverter designs and commercial products that work with the rtl-sdr. Luckily to help you choose one, blogger and amateur radio hobbyist KF7LZE has posted a rather extensive review of all the upconverter options available for the rtl-sdr.
The article can be found here.