I refer to Jim Sky's post about his "RTL Bridge" software:
http://cygnusa.blogspot.com/2014/07/rtl-meets-radio-skypipe-and-rs.html
http://radiosky.com/spec/RTL_Bridge_Help.html
http://www.rtl-sdr.com/radio-astronomy-rtl-bridge-radio-sky-spectrograph/
"...I have written an application that allows you to use inexpensive RTL dongle radios to feed my strip chart program, Radio-SkyPipe (RSP), and my Radio-Sky Spectrograph (RSS), with wideband data. The program is called RTL Bridge...I consider this experimental as of now, and invite others to test RTL Bridge with RSS and RSP. If you think you want to try it read the help file here. You will need to install RSS if you have not done so and if you already have it installed, you will need the new update. It is all in that help file. RSS is free by the way. This could be the start of a nice hydrogen line study for very little money."