A Useful ATU Circuit

This simple aerial tuning unit was described by Doug G4RGN in Sprat 78 and is a useful modification of the Z match. It uses a parallel circuit for 30 - 80 and a series tuned arrangement for the bands up to 10 metres The mode of operation is selected by a DPDT switch.

The outer inductor is 12 turns of 20 swg spaced one wire diameter on a polythene 35mm film canister, with the inner coil fitting inside of it. The latter was wound on a 20mm diameter former - a syringe body in the prototype, but other formers of the same size can be pressed into service. The capacitor on the TX side of the circuit is insulated from metal box.

Doug warns of RF the tingles from the grub screw of the knob on this control. It might also be worthwhile pointing out the risks involved in using syringes in this day and age!

The prototype matches a G5RV with a 1:1 SWR on all bands and such a unit would be a useful addition to the ham shack.

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