I've been looking into this for a couple of weeks.
I came into a little bit of money and was able to buy a Spectrum Analyser. Tuning into a local Radio FM Station was an unexpected thrill. Probably the most expensive FM Radio going but it proved a point that I could use it to analyse a signal and use the instrument.

I am following this set of pages

Hydrogen Line Radio Telescope

I've got hold of some LNA boards and the components but also I've decided to get hold of the pre built units as described in these pages.
The reason being as I am completely new to this arena and it's best to start to something I know works to help in the debugging of the inevitable issues that will appear.
So let the adventure begin ! :)