TO: ALL WOOD COUNTY ARES MEMBERS (OFFICIAL)
ALL ARES AND NON-ARES AMATEURS ANYWHERE (INFORMATION)
FROM: KEN HARRIS WA8LLM ARRL DISTRICT 3 EMERGENCY COORDINATOR
WOOD COUNTY EMERGENCY COMMUNICATIONS INC.
WOOD COUNTY BULLETIN NR 16.46 DATE: November 13, 2016
SUBJECT: POWER PROTECT DIODE
What is a Power Protect Diode? It is a diode that has been placed across the Positive and Negative power leads of many two way radios. The diode is connected in a reverse bias direction. That means that current should never flow through it. If current should ever flow it, that means it is a dead short across the main power leads. Since it is a dead short across the main power leads, that means a lot of current is going to flow. With any luck there are fuses in the power leads, and they are going to operate, that is, blow.
What would cause the Power Protect Diode to have current flowing through it? Since the diode is reverse biased, the only thing that would cause it to pass current is a reversal of the Positive and Negative voltage on the main power leads, or and high voltage spike on the power leads. In either case the diode is now forward biased, and more than likely going to protect you radio, or whatever device has the diode in it.
When the diode is forward biased and high current flows through it, the diode will probably be destroyed and will stay as a dead short. If the diode has been destroyed, that is very cheap insurance, since it may have saved your radio. The diode may only cost 50 cents, but it gave it's life to save a hundred dollar radio.
With any luck, you should be able to replace the diode, put in new fuses and be back on the air. It is possible to just remove the diode, replace the fuse and be back on the air. But, without replacing the diode, the next time there is a high voltage spike, or the power leads get reversed, you may have to buy a new radio.
(Idea for this bulletin is from Brent Rice, KD8DLX)
Ken Harris WA8LLM
Wood County WV