I've been making some progress in re-building what I am now calling the Junk Box SDR. As I mentioned the other day, I have built a small 5v power supply. I have since added another zener diode on the 5v side to protect that side of the supply (from what I don't know, but it's there nonetheless). I have also started wiring up the connections to the power supply board.
I'm trying to reduce USB noise as much as possible, so in addition to adding a number of ferrite beads to the USB cable, I am bringing it into its own small compartment. The two power wires and the cable's shield are dead-ended and covered with heat-shrink, and the two data wires are connected to a female USB connector that will be supporting the actual SDR dongle. I've also brought power wires from the power supply board into this small compartment, so that the SDR dongle can now be unplugged and removed more easily, should it need replacement (I'd still have to unsolder the antenna lead).
I've finalized the filtering scheme: I have one high-pass filter with a cutoff frequency of 1.5 MHz to reduce interference from local AM radio stations. I have a low-pass filter with a cutoff frequency of 30 MHz to reduce front-end overload from the many local FM radio stations. Lastly I have a 50dB pi attenuator. All of these are switchable, so they can be used as needed. The only issue I have is that there is no easy way to make these work from the front panel. Actually, the Junk Box SDR doesn't really have a front panel. This is somewhat annoying to me, and if I ever do one of these again I will design it from the ground up so that all of the controls are on one side and all of the wiring is on the opposite side. It's a bit messy as it is now, but it is a junk box project, so I've had to make do with what I could get my hands on. With the exception of the SDR, the upconverter, and the switches, everything in the Junk Box SDR actually came from my junk box, hence the name.
More photos to come.