Signedon dial: GENERAL RADIO CO. / CAMBRIDGE, MA
FunctionThe frequency of transmission or reception of a radio circuit is inversely proportional to the square root of both its capacitance and inductance. Tuning coils are one of the methods used to alter a circuit's frequency, by altering the circuit's inductance.
In this particular case, the inductance of the coil (which would be part of the circuit) is changed by turning the lever, which makes one of the points of electric contact move to a different location on the coil wires, changing the effective size of the coil. Less wire and loops between the two electric contacts means a smaller inductance.
Historical AttributesCruft
ProvenanceFrom the Cruft Laboratory, Harvard University.