With particular reference to Trio/Kenwood rigs

This idea has appeared a number of times in QRP magazines, including Sprat and the particular article I quote from was in Sprat 61, by G4MYB, when he describes how, by applying a negative voltage to the ALC pins of the TS520S's ancillary socket, power control down to milliwatts is possible. The circuit is as above, and it can be seen that only a 9 volt battery and a 220k potentiometer are needed, plus a bit of cable and a suitable box. The positive side of the PP3 goes to earth. The latter need not be screened as only DC is enclosed. The battery life will be long, a typical current being 34 microamps, passing through the pot. As the ALC arrangement is pretty standard in the range of Kenwood/Trio, it may be applied to other rigs than the TS520S used by G4MYB. In the case of the '520S, the negative voltage is applied to pin 6, whilst pin 4 is earth.

Other authors have described using a similar set up for various transceivers.

Frank G3YCC

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