Tune (tuning) indicator: a lamp in series with an adjustable inductance connected across a short length of the earth wire.

The lamp indicates by its brightness the current in the aerial circuit. The inductance is wound with 35 turns of bare copper wire on a grooved wooden core and a switch arm regulates the amount inductances in the circuit. In practice a position can be found where the flow of the lamp will increase to a maximum as the aerial circuit gets into tune, decreasing as the resonance point is reached.

The tune indicator was connected across about six feet of the earth lead from the jigger secondary, ST 021412. By adjusting the inductance until the lamp was brightest, it ensured resonance.

Tune indicator ST 021416 achieves the same result as ST 21422 but in a different way.

Physical Description

Wooden baseboard with two terminals and a lamp in a socket. A moveable arm connects the lamp to a slide contact on a coil.

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