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In case you decide to use a IRF9540N fo reverse polarity....

Mark Hatch
 

Ubitx.net has a lot of good suggestions to provide a solution to reverse polarity:

http://ubitx.net/ubitx-fix-reverse-polarity-protection/

But just a note on the last option (which I chose because it looked the easiest). The use of a p-fet like a F (bottom of page). In the diagram, the +Vin is attached to the Drain. Just be aware that the metal piece on the back of that device is also connected to the drain. So if you were to ground this....

I caught this before the magic smoke escaped. But thought I would pass this along.

73
Mark
AJ6CU

Mike Yancey
 

Oh, that's my preferred method, the P-FET.
Not only do you use an insulator, ya have to TEST it with a DVM. Sometimes if you (meaning ME, since i crank it) tighten down the attachment screw & nut enough, it'll cause some shorting to your case (or wherever you have it mounted.

I've used this on a Heathkit HW-8. Works a treat - nearly zero voltage drop.
On the BitX, I've chosen to Power-Poles, which are pretty good at keeping the bad polarities away...

Mike Yancey, KM5Z
Dallas, Texas, USA