RPP-1 This is a useful yet simple project that is ideal as simple way to protect your QRP radio (or any other low power product) from a very common wring mistakes.This will automaticly remove power from your sensitive electronics in the case that the supply is wired backwards. Feel free to use the instructions here to make your own RPP device, just one word of warning. I purchased a small number of MOSFET from a China supplier. they came and had the correct part number on them but the voltage drop across the module was nearly 0.5v, better than a diode but still not good. in the end I used MOSFETS from a more trusted source (RS Components) these are much more expensive but the voltage drop was much lower (0.1V - 0.17V at max current of 5 Amps). Buying cheap parts can be a mistake, Make sure you trust the source of your parts!.
Reverse Polarity Protection Module
Full Kit Instructions can be downloaded here (Use these to make your own if you wish