The satellite dish is designed for the 4Ghz band up to the 11Ghz band. If you have an 8` diameter dish, at 4Ghz the beamwidth is about 2.5deg. or so. With this in mind, you will be able to do some radiotelescoping with the dish from about 1Ghz (beamwidth of about 10deg.) to about 20Ghz (for the best of the dishes for shape with a beamwidth of about 1/2deg.).
Willmann-Bell has some books about radioastronomy and I bought one (and promptly got it stolen from me at work) that went through how to do a interfrometric array of antennas. If you can keep the phase of the two antennas good then you can do this. This means that you can`t do downconversion at the dish but must rather do it later in the signal path.