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The Autodyne or Self-Heterodyne Long-Wave Receiving Set.—This is the simplest type of heterodyne receptor and it will receive periodic waves from spark telegraph transmitters or continuous waves from an arc or vacuum tube telegraph transmitter.

The connections for the autodyne, or self-heterodyne, receiving set are shown in Fig.

With a long wave autodyne, or self-heterodyne receptor, as this type is called, and a two-step audio-frequency amplifier you can clearly hear many of the cableless stations of Europe and others that send out long waves.

The Autodyne, or Self-Heterodyne Receiving Set.—Where only one vacuum tube is used for producing both frequencies you need only a regenerative, or feed-back receptor; then you can tune the aerial wire system to the incoming waves and tune the closed circuit of the secondary coil so that it will be out of step with the former by 1,000 oscillations per second, more or less, the exact number does not matter in the least.

From this you will see that any regenerative set can be used for autodyne, or self-heterodyne, reception.