Alex - PA1FOX
The diode will short out if reverse polarity is done. Normally PSU have fuses and that will blow.
But yes an in line fuse would be advisable.
I prefer to use a a relay with a diode that will engage if the supply is reversed. the contacts can also be use to trigger an alarm or buzzer.
Yes, I use this relay method with my uBitx as well. The same relay is used to switch the rig to the built in batteries when unplugged from the external power supply. And in case of reverse polarity applied, the rig keeps on working on the built in batteries. I also plan to add an under/overvoltage protection: the relay will not switch when less then 11 volts or more than 15 volts are applied. This will keep the rig in a controlled supply voltage range whatever power supply is used. (ok.. don't use an AC power supply directly....)