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is added back into the input of the amplifier, and is amplified again. 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. The amplifier could be a single stage or multiple stages. It can be seen that since each active
45:(sound) signal (AF). It was first invented in 1914 by German scientists Wilhelm Schloemilch and Otto von Bronk, and rediscovered and extended to multiple tubes in 1917 by Marius Latour and William H. Priess. The radio signal from the antenna and tuned circuit passes through an amplifier, is
176:
The most common application of the reflex circuit in the 1920s was in inexpensive single tube receivers, because many consumers could not afford more than one vacuum tube, and the reflex circuit got the most out of a single tube, it was equivalent to a two-tube set. During this period the
136:
signal is fed back from the output of the amplifier to its input. In the reflex circuit it is only the audio extracted by the demodulator which is added to the amplifier input, so there are two separate signals at different frequencies passing through the amplifier at the same time.
148:. Since the two signals have different frequencies, they can be separated at the output with frequency selective filters. Therefore the proper functioning of the circuit depends on the amplifier operating in the linear region of its
203:
stage was also the first audio frequency stage using a reflex arrangement. That arrangement provided similar performance, in a four-tube radio, as one with five tubes. Often, but not always, such reflex receivers did not have
403:
normally has enough parasitic capacitance. The audio signal is applied to the grid of the tube and amplified. The amplified audio signal from the plate passes easily through the low inductance RF primary winding
20:
Reflex receiver from the 1914 Schloemilch and Von Bronk patent. The single triode vacuum tube amplifies the radio signal, then also amplifies the audio modulation signal extracted from it by the detector.
74:, required in the circuit, to reduce the cost. The economical reflex circuit was used in inexpensive vacuum tube radios in the 1920s, and was revived again in simple portable tube radios in the 1930s.
65:
through the same amplifier for audio amplification before being applied to the earphone or loudspeaker. The reason for using the amplifier for "double duty" was to reduce the number of active devices,
208:, and it was usually not possible to reduce the volume completely to zero, even at the minimum volume setting. At least one type of tube was specially designed for this kind of receiver design.
351:
which is tuned to the input frequency, serves as a second bandpass filter as well as blocking the audio signal in the plate circuit from getting to the detector. Its output is rectified by
123:
device (tube or transistor) is used to amplify the signal twice, the reflex circuit is equivalent to an ordinary receiver with double the number of active devices.
561:
164:
which can cause a shrieking in the earphone. The presence of the audio return circuit from the amplifier output to input made the reflex circuit vulnerable to such
594:
394:
provides more protection against feedback, blocking the pulses of RF from the diode, but is usually not needed since the transformer's winding
199:
The reflex principle was used in compact superheterodyne radio receivers from the 1930s and continued into the 1950s, until at least 1959; the
809:
196:
Low cost mains-powered radios that used a reflex TRF design, with only three tubes, were still being mass produced in the late 1940s.
509:
140:
The reason the two signals, the RF and AF currents, can pass simultaneously through the amplifier without interfering is due to the
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whose iron core serves as a choke to help prevent RF from getting back into the grid circuit and causing feedback. The capacitor
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which would block it. The amplified signal from the plate of the tube is applied to the RF transformer
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extracted by the diode from the RF signal is coupled back into the grid circuit by audio transformer
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shows one of the most common single tube reflex circuits from the early 1920s. It functioned as a
90:
The block diagram shows the general form of a simple reflex receiver. The receiver functions as a
182:
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Single tube reflex AM receiver, one of the most common reflex circuits, from the early 1920s
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controlled the filament current, and in these early sets was used as a volume control.
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is used to amplify the high-frequency radio signal (RF) and low-frequency
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receiver with one stage of RF and one stage of audio amplification. The
161:
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model F40 radio, a Super-Heterodyne receiver first manufactured in 1937.
333:
bypasses the RF signal around the headphone coils. The tuned secondary
276:
215:
178:
81:
628:"Baby GR Radio Astor brand, Radio Corporation Pty., Ltd.;, build"
608:(17). New York: Hennessey Radio Publications Co.: 3 July 8, 1933
102:) is amplified, then passes through the high pass filter to the
725:"Panoramic 11-60 Radio Kriesler Radio Company; Newtown, Sydney"
193:
were also made with some of their amplifier stages "reflexed".
701:"11-29 Reflex Radio Kriesler Radio Company; Newtown Sydney, b"
677:"556 Radio Stromberg-Carlson Australasia Pty. Ltd. Sydney, bu"
469:
The Design of CMOS Radio-Frequency
Integrated Circuits, 2nd Ed
450:
US Patent no. 1087892, Wilhelm
Schloemilch and Otto von Bronk
297:
bypasses the RF signal around the audio transformer winding
749:"6AD8, Tube 6AD8; Röhre 6AD8 ID21843, Double Diode-Pentode"
86:
Block diagram of a simple single-tube reflex radio receiver
595:"Reflexing Today: Operating economy with the newer tubes"
177:
demodulator was usually a carborundum point contact
550:, filed December 28, 1917; granted February 7, 1922
472:. UK: Cambridge University Press. pp. 15–18.
275:and is applied to the grid of the directly heated
126:The reflex receiver should not be confused with a
456:, filed March 14, 1913; granted February 17, 1914
152:. If the amplifier is significantly nonlinear,
360:, which was a carborundum point contact type.
236:(RF) signal from the antenna passes through the
654:Hill, John; Champness, Rodney (February 1996).
446:
444:
786:radio, a reflectional receiver from the 1920s.
534:. Wireless Press for RCA. pp. 1140–1141.
8:
547:Audion or lamp relay or amplifying apparatus
453:Means for receiving electrical oscillations
562:"The Story of Reflex and Radio Frequency"
493:
491:
489:
185:. However multitube receivers like the
61:, and the resulting audio signal passes
15:
504:. Murray Hill Books. pp. 283–284.
440:
544:US Patent no. 1405523, Marius Latour
528:Radiotron Designer's Handbook, 4th Ed
156:will occur and the audio signal will
7:
649:
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98:(RF) signal from the tuned circuit (
160:the RF signal, resulting in audio
14:
656:"The basics of reflex receivers"
413:and is applied to the earphones
201:intermediate frequency amplifier
181:, but sometimes a vacuum tube
1:
206:Automatic Gain Control (AGC)
810:History of radio technology
525:Langford-Smith, F. (1953).
836:
560:Grimes, David (May 1924).
154:intermodulation distortion
501:Radio's Conquest of Space
144:because the amplifier is
37:design in which the same
498:McNicol, Donald (1946).
29:, occasionally called a
466:Lee, Thomas H. (2004).
142:superposition principle
221:
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22:
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166:parasitic oscillation
129:regenerative receiver
106:, which extracts the
94:(TRF) receiver. The
92:tuned radio frequency
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31:reflectional receiver
27:reflex radio receiver
19:
753:www.radiomuseum.org
729:www.radiomuseum.org
705:www.radiomuseum.org
681:www.radiomuseum.org
632:www.radiomuseum.org
353:semiconductor diode
53:which extracts the
288:. The capacitor
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183:grid-leak detector
114:) signal from the
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820:Radio electronics
569:Radio in the Home
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815:Receiver (radio)
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663:Silicon Chip
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172:Applications
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120:audio signal
116:carrier wave
89:
78:How it works
68:vacuum tubes
62:
55:audio signal
30:
26:
24:
612:January 16,
602:Radio World
579:January 24,
168:problems.
104:demodulator
72:transistors
47:demodulated
804:Categories
784:neutrodyne
782:model 160
758:2020-03-10
734:2023-04-30
710:2019-04-07
686:2021-01-14
637:2022-07-10
575:(12): 9–10
479:0521835399
435:References
112:modulation
790:Schematic
776:Schematic
39:amplifier
665:: 88–91.
421:rheostat
162:feedback
158:modulate
51:detector
419:. The
226:(right)
212:Example
118:. The
59:carrier
33:, is a
508:
476:
324:while
277:triode
146:linear
110:(AF) (
659:(PDF)
598:(PDF)
565:(PDF)
532:(PDF)
179:diode
63:again
49:in a
43:audio
780:FADA
614:2016
581:2016
506:ISBN
474:ISBN
189:and
134:same
792:of
778:of
230:TRF
187:TRF
70:or
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646:^
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488:^
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25:A
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348:5
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