Reflex receiver

[2][3][4] It was first invented in 1914 by German scientists Wilhelm Schloemilch and Otto von Bronk,[1] and rediscovered and extended to multiple tubes in 1917 by Marius Latour[5][3][6] and William H.

At the output of the amplifier the audio is separated from the RF signal by the low pass filter and is applied to the earphone.

Therefore the proper functioning of the circuit depends on the amplifier operating in the linear region of its transfer curve.

Low cost mains-powered radios that used a reflex TRF design, with only three tubes, were still being mass produced in the late 1940s.

The radio frequency (RF) signal from the antenna passes through the bandpass filter C1, L1, L2, C2 and is applied to the grid of the directly heated triode, V1.

The resulting audio signal extracted by the diode from the RF signal is coupled back into the grid circuit by audio transformer T1, T2 whose iron core serves as a choke to help prevent RF from getting back into the grid circuit and causing feedback.

The capacitor C4 provides more protection against feedback, blocking the pulses of RF from the diode, but is usually not needed since the transformer's winding T1 normally has enough parasitic capacitance.

Reflex receiver from the 1914 Schloemilch and Von Bronk patent. [ 1 ] The single triode vacuum tube amplifies the radio signal, then also amplifies the audio modulation signal extracted from it by the detector.
Block diagram of a reflex radio receiver
Block diagram of a simple single-tube reflex radio receiver
Single tube reflex AM receiver, one of the most common reflex circuits, from the early 1920s