Engineering Dictionary of Terms
"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"

Autodyne Circuit

An Autodyne circuit combines three functions normally found in different stages in an RF Receiver into a single circuit. However the three stages which are the RF amplifier, the Mixer and the Local Oscillator are normally found concatenated together. Although each stage in a normal receiver would have an individual amplifier. In the case of an Autodyne design, the RF amplifier, mixer and oscillator use the same transistor amplifier

Transistor Autodyne Amplifier Circuit
Autodyne Circuit

The RF amplifier stage is that portion of an RF receiver that receives a signal from the antenna and amplifies the signal so that it is usable by the following circuitry. In regards to this example the RF amplifier would have been a low-noise high-gain transistor amplifier circuit.

The Mixer Circuit would be attached, and follow the RF amplifier and use its own transistor [or other device] to combine the RF signal with the signal generated from the local oscillator. The mixer stage would then output its signal to the IF stage.

The Local Oscillator circuit is designed to output a frequency that when mixed with the incoming RF will produce the correct Intermediate Frequency [IF] used by the rest of the circuit. Normally the Local Oscillator [LO] is designed to function as a stand-along circuit.

The Autodyne circuit shown above combines all three functions into a single design, using one transistor as both the amplifier and combiner. The circuit amplifiers the RF, functions as an oscillator and mixes the two signal together.

Autodyne Circuit Variations

The Autodyne schematic is just an example. The PNP transistor could just as well be an NPN type, a FET or any other amplifying component. In addition, the Common-Emitter circuit used is just one of three possible configurations for a transistor.

The style and type of oscillator could also take any form, this one appears to be a Hartley Oscillator. Also the methods of feed-back could be altered as shown on the Armstrong Oscillator page.

Finally the resistors used to bias the circuit could change position, or bypass capacitors could be added. No values are provided because they would have to change depending on the frequencies involved, the in coming RF, the LO frequency and so on. So in general the schematic is only meant to advance the definition of an Autodyne circuit, without going through the steps needed to design such a circuit.

Editor Comment: Use the dictionary links above or to the right to research any terms or functions used on the pages, or terms that might be related. Each dictionary is it's own section, with individual links near the top of their pages. Many entries show additional graphics, or variations to different circuits.

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