Hi, Well it's nothing so special the idea is from a book called Homebrew Cookbook by a fellow Radio Amateur called Eamon Skelton EI9GO it's of modular construction,and consists of Noise Source,Mixer-Product Detector,Crystal Oscillator ,AF amp. I built this one for checking the response of Crystal filters, the best software is the registered version of Zeloscope.
With that behind me I'm building a version of poor-mans spectrum analyser, using the block diagram as a map, with my own versions of the blocks, it's the only way to learn. as with the first S/A the building blocks I changed to make my own versions I want it to work with my scope,rather than software, it's a great way you learn especially when it works.
There is a Vector Network Analyser home brew, that fascinates me a lot .hope this helps a bit, I found just concentrating on a small part of the circuit at a time helps.