Powering a hand held transceiver from an AC power supply

Do you have an FM 2 Metre hand held (or 70 or 23 Centimetre FM hand held), you wish to power your hand held from a well regulated and filtered power supply but there is only provision to power the unit from either a nickel-cadmium battery pack or a dry cell battery pack?

If your hand held includes a dry cell battery pack (or one is still available), then read on.

Firstly, ENSURE THAT YOUR REGULATED AND FILTERED POWER SUPPLY IS CAPABLE OF SUPPLYING THE NECESSARY CURRENT AND THAT ITS OUTPUT VOLTAGE IS WITHIN THE MAXIMUM LIMIT THAT YOUR HAND HELD TRANSCEIVER CAN SAFELY HANDLE. AND ALSO ENSURE THAT YOU OBSERVE THE CORRECT POLARITY!

As close as possible to the power connector strips, drill a hole adjacent to each strip and place a screw into both holes. After placing a nut onto the screw and tightening it, the edge of the nut should make good electrical contact with the strip on the proviso that you have put the hole close enough to it. For good measure, you could place an "eye terminal" under each nut to ensure good contact.

For the screw that is making contact with the -ve (negative) power connector strip, place an "eye terminal" under the screw head and connect this to the -ve lead from the power supply.

Drill a third hole in the battery pack case and insert a third screw with an eye terminal underneath the head and place a diode with sufficient current rating between this third screw and the screw making contact with the +ve (positive) power connector strip. The purpose of the diode is to protect your hand held from accidently connecting the power with the wrong polarity. The +ve lead from the power supply is now attached to this third screw. YOU SHOULD ALSO PUT A SUITABLE FUSE SOMEWHERE IN THE +VE LEAD!

And now you can power your FM hand held from an AC power supply.

Submitted by John L WICKHAM VK3ZK Cranbourne, Victoria, Australia.