266,178. Jackson, L. Mellersh-, (Lorenz Akt.-Ges., C.). May 14, 1926. Frequency, changing.-In wireless signalling systems, harmonics, side frequencies, and other undesired frequencies are eliminated from a circuit bv an ironcored transformer, the primary coil of which is in the said circuit, the secondary coil being tuned to the desired frequency. The Figure shows the device applied to a wireless transmission system employing a frequency-multiplier Tr feeding an aerial through a circuit comprising a condenser C, a coupling coil K and the primary coil w1 of the iron-cored transformer F. The secondary coil w2 is in circuit with an additional coil Land a tuning-condenser Cs, by which the secondary circuit is tuned to the desired signalling-wave. It is stated that unwanted frequencies are eliminated by the losses in the iron core whilst for the desired wave the resonance current in the secondary coil annuls the field of the primary coil, The transformer F should have low leakage. The secondary coil may be constituted by a portion of the primary coil.
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