20100528

After a whole lot of fiddling and various non-working designs, I've come up with this!

It uses two Mini Circuits ADE-1LH+ mixers, Xpresso 50 and 100 MHz oscillator modules, two MAX2611 LNAs (front end and IF), and spits out 150-155 MHz-ish signals at baseband. The system gain is about -5 dB - it requires a high gain amplifier at baseband to be useful. The MAX2611s aren't particularly high gain and there are many losses in the passive mixers and all of the 3 dB pads. I'll build some sort of amplifier and will then be able to compare its performance to the dual SA602 design.

Key design point:

• Top layer ground plane fills are a huge, huge pain when you don't have a solder mask, especially when your PCB design software uses, by default, a clearance of only about 5 mil from tracks and pads! I spent more time hunting down and fixing bridges than actually placing components. In future, increase this margin massively.
• Use of sticky tape to affix toner transfer paper is fraught with danger - a missing strip of ground plane is evident toward the top of the board where the melting tape interfered with heat transfer in the laminator.