Reflex Radio Receivers

A reflex radio is one in which a single amplifier is reused to first amplify an RF (or IF) signal, and then amplify the AF produced by a separate  detector.  As long as the amplifier operation remains linear, there is no interference between the RF and AF signals.

The original circuit was patented by a couple of Germans in early 1914.  Later the U.S. Navy siezed the patent, and released it to to the public after WWI.

Obviously, this reduces the number of active devices required, and cuts cost and power consumption.

The Story of Reflex
and Radio Frequency

An interesting article by David Grimes, inventor of the Grimes Inverse-Duplex radio, from Radio in the Home, May, 1924.
A Short-Wa4ve Reflex from 1924

The N3FRQ - "Skyflex"

A one-tube reflex set using a single 12-volt auto-radio tube, desined in 2002.

Homebrewers in other  parts of the world have paid more attention to reflex radios than we in the U.S.
  Here a collection of articles from UK publications;

Reflex Transistor Radios

Tne Sinclair Micro-6

A Truly Amazing Reflex Circuit from Russia - 1993

Radio, 1993, 9

This is a very simple reflex radio receiver for Middle Wave band. It needs no adjustment and consumes very low current (1..2 mA) in operational mode. The receiver is based on direct amplification circuit with one tuned tank circuit (fig. 1). The induction coil L1 and L2 is wound on a ferrite rod (a loopstick antenna) or a frame (a loop antenna). Variable capacitor C1 is used for tuning radio receiver....

English Article Here.

Article from the Russian journal
Radio, September 1993

Reworked schematic using Western components.

The N3FRQ solar version

LT-Spice file - Russian Reflex CK2.asc

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