Audion
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 A historical Audion receiver. An audio tube is attached (left) |
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| Device / component | |||
| Class: | Straight-ahead receiver | ||
| Invention: | 1st half of the 20th century | ||
| technology | |||
| Power supply: | Operating current and, for tubes, additional heating current | ||
| Active components: | Minimum 1 tube triode or transistor | ||
| Playback via: | Headphones or speakers | ||
| Frequency band: | Depending on the attached or built-in antenna coils, long / medium and short wave (VHF possible to a limited extent) | ||
 Circuit example of a simple Audion receiver |
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The Audion is a straight-ahead radio receiver and is often a single circle . Lee De Forest , the inventor of audion, formed the word from the Latin word audio , I hear. In 1907 De Forest patented the audio tube and the audio circuit. From 1909 De Forest sold the Audion RJ-4. The amplifier component in the audio circuit amplifies the received high frequency and converts it into an audible low frequency ( demodulation ). With feedback audio or regenerative receivers, part of the amplified high frequency is fed back to the input of the amplifier component for further amplification. The audion was more sensitive than the detector receiver , but less sensitive than the heterodyne receiver . In Germany from 1926 the Audion OE333 and later the feedback audio RO433 from Loewe were very successful because of their low price. Later the Volksempfänger VE301 and DKE used an audio circuit with one to three tubes. After the Second World War, the Heinzelmann was built as an Audion in the FRG and the 1 U11 in the GDR .
A few years after the Second World War, the need for more powerful radio receivers for medium and ultra-short waves increased more and more, so that the more powerful - but more complex - superhet or heterodyne receivers were built. With the subsequent switch from tube radios to transistor radios , audion almost completely disappeared from industrial production for high-performance radio receivers.
Definitions
The term audion is used in electronics and electronic circuit technology in various and sometimes overlapping meanings, which are shown below.
Component
The term audion goes back to the name Lee De Forest chose for the gas-filled triode he invented and used in an audion circuit. With the first audio tubes, the directly heated cathode - a tungsten filament - was in the middle, the control grid on the left and the anode on the right. The arrangement of the filament, control grid, anode one behind the other resulted in better reinforcement. The amplification was further increased in the double wing audion. A control grid was attached to the left and right of the filament and an anode behind it. The two control grids were connected to each other, as were the two anodes. At first only the gas-filled triode according to de Forest was understood by the audio tube. Later, a high vacuum electron tube, which was used in an audio circuit, was also called an audio tube.
Electronic switch
In the De Forest patent of 1907, in addition to the audio tube, the audio circuit, which was later called grid audion, was presented . Without an input signal, the grid operating point of the electron tube between the starting current area and the space charge area is approximately 0 V. There are several causes for the envelope curve demodulation . Once the grid current I g occurs only with a positive grid voltage U g . See the electron tube characteristics of the RE064 on the right. The grid is more highly resistive for negative grid voltages than for positive grid voltages, and the grid voltage U g characteristic curve is curved to the anode current I a . Higher grid voltages are amplified better than lower grid voltages. The audio stage is a high frequency amplifier that amplifies positive and negative half waves differently. The amplified high frequency at the output is fed back to the input during a feedback audio . A low pass at the output supplies a voltage which corresponds to the envelope curve of the high frequency.
The audio circuit with triode shown on the right works with a grid combination . The grid combination allows a small negative voltage to develop on the grid, see starting current law . This grid bias results in a grid operating point that puts less load on the resonant circuit. The grid combination has another effect for high input voltages. The tube diode between grid TG and cathode TK, together with smoothing capacitor C2 and load resistor R1, forms a rectifier circuit . Due to the polarity of the diode, the right side of the capacitor carries a negative voltage compared to the left side. This voltage becomes more negative as the HF input voltage rises and ensures an operating point shift ( sliding operating point ) through the peak value rectification of the tube diode.
The grid combination is not absolutely necessary for the audio function. According to de Forest, the grid combination increases the sensitivity. Whether this is the case depends on the characteristics of the amplifier component and the rest of the circuit.
In the circuit shown, internal resistance R i between anode TA and cathode TK of the tube and C3 form a low-pass filter for low frequency. In this case, the anode resistor with an impedance of 4000 Ω is a pair of headphones, labeled “HOERER” in the illustration, with which the fluctuations in the anode current caused by the amplitude modulation can be heard.
A low-frequency amplifier is connected to the anode resistor of the audio stage via a coupling capacitor. This RC coupling is common with a pentode as an audio tube. When using a triode as an audio tube, the transformer coupling was used first. The transformer had a voltage transfer ratio of 1: 4 and matched the low-resistance anode circuit of the triode to the high-resistance grid circuit of the LF amplifier tube. The transformer was an expensive component with a rather poor frequency response, which is why the RC coupling was later used for triodes as an audio tube, even if a higher voltage gain could be achieved with transformer coupling.
Radio receiver
An audion is a receiving device as a whole, in which an audion stage or circuit is used and this is often supplemented by an RF amplifier before the audion stage and an AF amplifier afterwards to achieve greater volume. A common name was 0-V-2. That meant zero RF amplifier stages, audio stage and two LF amplifier stages.
The circuit diagram of the Loewe-OE333-Audion shown on the right contains three triode systems. Together with the resistors and coupling capacitors C2, C3 and R1 to R4, they were housed in a common glass bulb (multiple tube 3NFB). The left triode works as an RF amplifier, the middle one as an audio stage (grid demodulation) or LF preamplifier and the right one as an LF output amplifier. With the 3NFB it was also possible to set up a feedback audio , whereby an RC grid combination was used in front of the first grid and a tapped input circuit was required for the correct phase feedback. The first triode thus worked as an audion (HF amplification, demodulation and NF amplification).
The Loewe 3NF tube from 1926 can be seen as the first "integrated circuit". Like today, the tricky construction included all "integrable" components. Since the resistors were not suitable for high vacuum, they were encapsulated in glass.
Exceptions
Occasionally there is talk of an audion arrangement, although in connection with an amplifier effect it is not a question of simultaneous demodulation: in other circuits that work with tubes, the principle of generating grid bias by rectifying the input signal can also be found - especially in various oscillator circuits and in In special cases, even with amplifier stages (especially transmitter stages), the operating point is set by means of grid rectification in accordance with the audio stage. Whether demodulation or only bias voltage generation or operating point setting is present depends on the time constant of the grid combination. If it is sufficiently small, it can be used to demodulate a low-frequency signal.
Controversial definitions
The definition of audion accepted today is amplification and demodulation in one and the same amplifier component. If the term audion is understood as an amplifier stage with feedback, then the de Forest Audion circuit from 1907 is not an audion because it works without feedback. If audion is understood as an amplifier stage that performs several functions at the same time, the audion cannot be separated from the reflex receiver . Since the demodulating audio stage in principle amplifies both the low frequency demodulated at the grating and the high frequency, such a combination is possible ( feedback audio ).
history
see also → Invention of the radio
The beginning of broadcasting
In 1907 de Forest patented the Audion (see circuit on the right). The antenna and earth are connected to coil I 1 . The resonant circuit I 2 , C is coupled inductively. The grid combination consists only of the capacitor C '. With gas-filled tubes, the ion current between the grid and cathode makes a grid bleeder resistor unnecessary. In the audio tube D, F denotes the directly heated cathode, a the control grid and b the anode. The headphone T is in the anode circle. The heating battery is designated A, the anode battery B. The designations A-battery and B-battery are likely to go back to this patent drawing.
The de Forest RJ-4 contained an audio stage, but no oscillating circuit, and was sold from 1909. The American radio amateur Paul E. Wallace sold the Wallace Valve Detector , the first Audion radio receiver , from 1911 .
In 1913 Irving Langmuir and William C. White were able to manufacture the high-vacuum triode Pliotron with a vacuum pump designed by Wolfgang Gaede . The audio circuit for high vacuum tubes had an additional grid leakage resistor and was otherwise identical to the circuit for the audio tube.
The feedback audio without RF amplifier will be sent to the transmitter if the feedback is set too strong. The transmitted signal generated disturbs neighboring receivers. In order to limit the problems, Germany needed an audion attempt permit from the Reichspost until 1925 .
The first electron tubes had tungsten filaments. The gain of these early tubes was modest. During the First World War, Western Electric and General Electric in the USA, Siemens & Halske and AEG in Germany, Marconi in England, and Grammont and Compagnie Générale des Lampes in France developed high-vacuum triodes. After the war, these tubes and their successors were used in audions for radio reception. These radios were operated with a lead accumulator for heating and a dry cell battery for the anode voltage.
An audion with one or two triodes provided enough volume for headphones. Early audions for loudspeaker operation had up to eight triodes. After the introduction of the pentode in 1927, two to three tubes were sufficient for an audion with loudspeaker operation. The output power was modest. The pentode RES164d had 0.5 W speech power with 10% distortion factor at 100 V anode voltage.
A variety of feedback audio circuits have been developed. The superhet receiver is not, however, a direct further development of the audio. One of the first superhets, the RCA Radiola Superheterodyne AR812 from 1924, contained an audio stage for demodulation. At that time there were no composite tubes with a diode and triode system. Later, tube diodes were mainly used as demodulators in the heterodyne receiver , so that the audio circuit lost its importance here.
Significance at the time of the 3rd Reich
Although the state of receiver technology was more advanced in the 1930s, the audion principle continued to be of great importance, as it was mainly to be found in the various types of popular receivers . One advantage was that the devices were cheap to manufacture at that time and could therefore be offered at a low price, so that an ever larger part of the population could participate in radio reception.
In this sense, the poorer reception performance compared to the superhet should have been desired in order to at least make it more difficult to receive stations from other countries. However, popular receivers produced later were more sensitive than their predecessors. This product improvement contradicts the above assumption.
The post-war audion
After the Second World War, the audion initially retained a certain importance, mainly due to the shortage. Radios that were not confiscated by the victorious powers were repaired in many places and several defective devices were merged into a functional one. The audio circuit had the advantage that it was easy to see through and that hardly any special components were required.
Until the post-war period, feedback audio with fixed feedback was found in radio receivers known as dwarf or small super as an intermediate frequency stage for amplification and demodulation.
The legendary “ Heinzelmann ” radio kit from Max Grundig from 1947 was also an audion and the basis for the economic success of what would later become Grundig AG .
present
The first commercial transistor radio with bipolar transistors Regency TR-1 from 1954 already used the superhet circuit. Even later, only a few transistor radios were built using the Audion circuit. Still available today, however, are the MFJ-8100K from MFJ Enterprises and the 1253 from Ten-Tec, both of which are designed to receive shortwave. Both devices are supplied as a kit, the first is available in the W version (wired), but also fully assembled.
A number of “Audion circuits” with bipolar transistors have been presented in specialist books and journals. The demodulation takes place on the curved characteristic of the base-emitter diode of the transistor. In individual cases, circuits were also referred to as “audions” in the literature, in which a separate diode was used for amplitude demodulation , with a direct current coupling then generally being present between the diode and the amplifier component.
The field effect transistor is to be regarded as an equivalent component to the electron tube. Both components are voltage-controlled (powerless controlled) amplifier components. The bipolar transistor, on the other hand, requires input power. The JFET gate has a very high resistance (no power) for negative input voltages, because the PN junction in the JFET is then operated in reverse direction. The JFET gate has a low resistance for positive input voltages because the PN junction works in the forward direction. An audio stage with JFET hardly differs from an audio stage with an indirectly heated pentode.
In addition to various kits - such as those already mentioned by MFJ and Ten-Tec - you can find innumerable instructions for building transistorized Audion receivers in the literature and on the Internet , so that a certain importance of the Audion in hobby electronics has been retained.
By switching off many powerful radio transmitters in the medium wave range, fewer radio stations from Europe can now be received with audio receivers than 25 years ago.
Mode of action
The functions of the Audion as a receiver stage or circuit are:
- the demodulation of the amplitude-modulated high frequency received by the antenna in the active component, for example on the curved characteristic of the control electrode.
- an LF amplification of the demodulated signal.
- usually also a high-frequency amplification of the reception frequency , this purpose being served by a feedback that can usually be set externally . With suitable adjustment, it improves the effective circular quality of the tunable resonant circuit used for frequency selection as a result of the associated undamping , so that the selectivity is increased at the same time.
The principle is the demodulation of an amplitude-modulated signal with an envelope detector in combination with an amplification. The purpose of this multiple use of a stage can be to save (at that time more expensive) amplifier components (tubes, transistors), but also to obtain a simple circuit that is better suited for demonstration purposes, building instructions and kits.
Grid audion
After further circuits for simultaneous demodulation and amplification by means of radio tubes were worked out, some authors used the terms grid rectification (grid audion), anode rectification (steep audion) and rectification as a result of current distribution (braking audion) to distinguish them. The grid audio is the audio circuit described above .
The grid combination can be implemented in different designs for grid audion. A parallel connection of C and R was common with indirectly heated tubes. In the case of directly heated tubes, the resistor was placed between the grid and the negative or positive filament end. The capacitor should be ten times larger than the input capacitance of the amplifier component. Values of 100 pF and 220 kΩ are suitable.
The grid audion is better suited for small input voltages than the anode rectifier. The grid voltage is higher than with the anode rectifier, which means that the gain is also higher. At higher input voltages, in addition to grid rectification, anode rectification occurs, which distorts the LF signal.
Anode rectifier
The steep audion or the directional amplifier are treated under anode rectification . Compared to the grid audion, the steep audion is less suitable for small input voltages because it is less sensitive, but better for larger input voltages because these can be demodulated with little distortion. The audio stage in a superhet after the IF amplification was mostly an anode rectifier. Because of the working point of the steep auditory, the use of feedback is tough. If you change the feedback adjuster slightly, the audio will abruptly switch between amplification and oscillation. The steep audion requires a negative grid tension. A sliding working point and thus also a grid combination is not sensible for a steep audion.
Brake audion
According to Barkhausen, the input signal is at the anode during brake audion and the output signal is tapped at the grid. The cathode current I k was typically 0.5 mA, and the anode voltage was 3.5 V too. The grid voltage was high and the heating current so low that the cathode supplies the saturation current. This works best with a tungsten cathode. The demodulation takes place on the curved characteristic curve from anode current I a to anode voltage U a . See also Barkhausen-Kurz oscillation and Dynatron for further circuits with U a <u g .
Feedback audio
The feedback audion, the regenerative receiver or the ultra audion was the audio circuit with the greatest importance. In addition to the two functions of amplification and demodulation, there was also positive feedback. The positive feedback increased the amplification of the audio level by a factor of 10 to 20 as well as the selectivity by de-attenuating the resonant circuit. The triode UX199 from 1925 had a voltage gain of only 6.6. At a time when a typical radio receiver consisted of one or two triodes, this gain increase was therefore very welcome.
The feedback was patented almost simultaneously by different people. Alexander Meißner's oscillator used feedback and was patented in April 1913. The high-frequency amplification with feedback and subsequent demodulation was patented by Telefunken in July 1913 . In October 1913 Edwin Howard Armstrong registered his regenerative receiver , which also uses the tube for demodulation. Lee de Forest called his circuit ultra audion . After all of these patents were recognized by the patent offices, litigation began. Armstrong and de Forest argued until 1934. In the end, the Audion patent was awarded to de Forest. The company Western Electric registered several Audion circuits in 1915 as US Patent 1330471 through its employee Burton W. Kendall. The Fig 2 Audion shown on the right uses the Hartley oscillator circuit and adjusts the feedback with a potentiometer.
The circuit of the feedback audio Loewe RO433 from 1928 shown on the right uses feedback according to Gustav Engelbert Leithäuser . The resonant circuit coil L 2 has an additional feedback winding. The amplifier component has a phase reversal (180 °) between input and output. The feedback winding is connected in such a way that there is a further phase shift of 180 °. A phase shift of 360 ° results in positive feedback. The variable capacitor C 5 is used as an adjustable attenuator and controls the strength of the feedback. The correctly set feedback compensates for the oscillating circuit losses (undamping). However, if the feedback is set too strong, the circuit works as an oscillator and sends out radio waves itself, so that reception in the neighborhood can be disturbed.
The feedback audio has been displaced by the overlay receiver . The reasons were the difficult operation of the audio (2-button operation), the imprecise frequency scale , the dependency on the antenna , the distortion ( harmonic distortion ) with strong transmitters, the lack of automatic fading , the relatively low selectivity , the feedback-dependent audio frequency response as well the risk of undesired and forbidden radio wave emission if the feedback is set too strong, which leads to so-called feedback whistling. However, it is precisely this kind of feedback that makes it possible to receive Morse code and single sideband telephony (SSB). The “feedback whistling ” in the headphones is caused by the difference between the audio oscillation frequency and the carrier frequency of the transmitter to be received: if both frequencies match, the difference frequency is zero and there is no longer any whistling sound. This was used by the user as a coordination aid (“whistling”), but led to the aforementioned disturbances for the neighborhood.
The transmission as a result of excessive feedback can be prevented by limiting the feedback, decoupling the audio stage from the antenna using high-frequency preamplifiers and shielding the audio stage. The frequency of the natural oscillation was very dependent on the environment in simple devices without a high-frequency pre-stage or in devices without shielding, so that the pitch changed as soon as the hand of the radio listener moved towards the device. This effect is also used for one of the first electronic musical instruments - the theremin - in which a second oscillator leads to superimposition instead of the transmitter frequency.
Pendulum Audion
The pendulum audion or the pendulum receiver are treated under super regenerative receivers . The greatest advantage of the pendulum receiver is the one-button operation. There is no feedback adjuster. The working point of the feedback audio in the pendulum receiver changes constantly. This also changes the receiving frequency. Because a larger reception bandwidth is recorded and converted into a smaller low-frequency bandwidth, the noise in the headphones is greater than in feedback audio. The higher sensitivity of the super regenerative receiver is an advantage over the other audio circuits.
Transistor audion
The transistor Audion uses transistors as an amplifier components. A transistor audion was first set up with bipolar transistors , after the appearance of the field effect transistors also with these. With transistors, audio circuits without feedback and with feedback as well as pendulum receivers were built. In the case of bipolar transistors, the demodulation results from the curvature of the base-emitter-diode characteristic, similar to a steep audion. The JFET behaves almost like an indirectly heated pentode. Negative half waves bring the PN junction in the reverse direction, positive half waves bring the PN junction in the forward direction. According to radio amateur Charles Kitchen, transistor audions with JFET work better than those with bipolar transistors. Today radio amateurs and amateur electronics enthusiasts also build superhet receivers or software-defined radio receivers in addition to audions because the necessary components such as integrated circuits and quartz filters are available at low cost.
The Audion shown on the right with a bipolar transistor works without feedback. The resonant circuit consists of L1, L2 and C1. The two coils L1 and L2 form an autotransformer. The HF voltage at L2 is only a fraction of the HF voltage at C1. For this, a higher current can be drawn from the resonant circuit at L2. The bipolar transistor has a low input impedance in common emitter circuits. The base is adapted to the resonant circuit by the autotransformer. The grid combination consists of R1, R2 and C2. The best possible demodulation is set with the adjustable resistor R1. The resistors are connected to the positive terminal of the battery BAT. An npn transistor requires a positive voltage at the base. The capacitances in the transistor can form unwanted resonant circuits with inductances outside the transistor. R3 is a series resistance in these oscillating circuits and dampens wild oscillations of the undesired oscillating circuits. R4 is the working resistance. R4 turns the fluctuating collector current into a fluctuating voltage at the collector. The low pass L3, C3 only allows the low frequency to pass. Via the coupling capacitor C4, the NF is fed to the consumer RL without direct voltage.
The feedback audio with JFET works in the circuit presented by FH Schnell. The resonant circuit consists of L1A, L1B and C1. The antenna is coupled via C2. As with the Audion with a bipolar transistor, the coils L1A and L1B form an autotransformer. Due to the low-resistance connection of the antenna, the antenna capacitance has less of an effect on the resonant circuit than if the antenna were connected to C1 with high resistance. The grid combination consists of R2 and C4. The feedback is from the drain of the FET through capacitor C3 to feedback coil L1C. The adjustable resistor R1 determines the strength of the feedback. With the quick connection, the components for setting the frequency and for feedback are each connected to ground. This reduces the sensitivity to hand capacity. The HF choke L2 prevents the high frequency at the drain from being short-circuited via R3 or C7. R3 is the working resistance at which the low frequency is coupled out via C7. R4 ensures a small positive voltage at the source or a negative gate bias, similar to the automatic grid bias generation or operating point setting for electron tubes. C5 and C6 are used to block or prevent current negative feedback from R4.
Reflective audio
The amplifier component in the feedback audio is switched in such a way that a negative differential resistance or a falling characteristic curve results. With the reflex receiver , different signals (HF and LF) are amplified in the same amplifier component. The signals are superimposed at the input and separated again at the output. A separate component (diode) is used for demodulation. With a linear amplifier the superimposed signals do not influence each other. In addition to amplification, audion also means demodulation in the same component, and demodulation requires a curved characteristic. A reflection audio is a bad compromise from times when transistors were still very expensive. The amplification must be linear enough so that the reflex principle still works, and at the same time it must be sufficiently non-linear so that the audion principle already works.
The "Reflexaudion" shown on the right shows a reflex receiver with feedback. The use of the term reflex audion is controversial. There are indications that this designation could originally refer to circuits that change from reflex to audio reception depending on the signal strength.
literature
- H. Barkhausen: electron tubes 4th volume. Rectifier and receiver . 6th edition. S. Hirzel, Leipzig 1951.
- Friedrich Benz: Introduction to radio technology . 3. Edition. Springer Verlag, Vienna 1944.
- Rolf Wigand: Correct radio tinkering, Part 1. Simple receivers from the detector to the feedback audio . 5th edition. Hachmeister & Thal, Leipzig 1942.
- Radio technology annual folder 1948: circuit descriptions, market overview.
Web links
swell
- ^ L. de Forest, US Patent 879532 , Space Telegraphy, filed Jan. 29, 1907
- ↑ RJ-4 receiver, Roger DeForest Collection
- ↑ OE333 receiver, H.-T. Schmidt
- ↑ L. de Forest, US Patent 841387 , Device for Amplifying Feeble Electrical Currents, filed Oct. 25, 1906, Fig. 2
- ^ L. de Forest, US Patent 879532 , Space Telegraphy, filed Jan. 29, 1907, Fig. 1
- ↑ Wolfgang Holtmann, Die Geradeaus-Receiver , Section 4. The Function of the Audion
- ↑ Helmut Schweitzer, Funkschau, Heft 22/1988, Audion - Kleinsuperhet , section physical basics
- ^ L. de Forest, US Patent 879532 , Space Telegraphy, filed Jan. 29, 1907, p. 1, line 104: find that the presence of said condenser produces a great increase in the sensitiveness
- ↑ https://www.radiomuseum.org/tubes/tube_3nfb.html Wolfgang Holtmann: Description of the 3NFB in Radiomuseum.org
- ↑ Patent US879532 : Space Telegraphy. Registered on January 29, 1907 , inventor: Lee de Forest (The Audion).
- ↑ L. de Forest, US Patent 841387 , Device for Amplifying Feeble Electrical Currents, filed Oct. 25, 1906, page 2, line 54: "an evacuated vessel inclosing a sensitive conducting gaseous medium"
- ^ Roger Deforest website link
- ^ Advertisement for Wallace Valve Detector, Modern Electronics . November 1912, p. 843 .
- ^ Pliotron, Udo Radtke Collection
- ↑ Rainer Steinführ, "At least at night Europe reception was often possible". link
- ↑ Otto Kappelmeyer: straight-ahead receiver repair internship. Jacob Schneider Verlag, Berlin-Tempelhof 1947.
- ↑ Helmut Schweitzer: Funkschau. Issue 22/1988, Audion - Kleinsuperhet
- ↑ Werner W. Diefenbach: Standard circuits of broadcast technology. 1942.
- ↑ Karl Schultheiss: The shortwave amateur. Franckh'sche Verlagsbuchhandlung W. Keller & Co., Stuttgart 1955.
- ↑ Heinz Richter : Transistor Practice. Franckh'sche Verlagsbuchhandlung, 1959, p. 129.
- ↑ Hans-Joachim Fischer: Amateur radio - a manual for the shortwave amateur. Franckh'sche Verlagsbuchhandlung W. Keller & Co., Stuttgart 1962.
- ↑ MFJ Enterprises MFJ-8100W product page (English) Link
- ↑ Ten-Tec 1253 product page (English) Link
- ↑ Heinz Richter: New Bastelbuch for Radio + electronics. Franckh'sche Verlagshandlung, Stuttgart 1957.
- ^ Karl-Heinz Schubert: Amateur radio. Military Publishing House of the German Democratic Republic, Berlin, 5th edition 1978.
- ^ Siegfried Wirsum: "Radio tinkering with field-effect transistors" . Radio RIM . Munich, 1973. Page 7ff.
- ^ H. Barkhausen : Electron tubes. 4th volume. Rectifier and receiver. S. Hirzel Verlag, 1937, p. 97 ff.
- ^ I. Gold: Radio internship. Verlag Hallweg Berlin, 3rd edition 1948, pp. 162/163.
- ^ H. Barkhausen : Electron tubes. 4th volume. Rectifier and receiver. S. Hirzel Verlag, 1937, p. 181, formula (149).
- ↑ Telefunken, Alexander Meissner, DE Patent 291604 , “ Device for generating electrical vibrations”, patented April 10, 1913
- ↑ Telefunken, DE Patent 290256 , receiving device for wireless telegraphy, patented from July 16, 1913
- ↑ EH Armstrong, US Patent 1113149 , Wireless Receiving System, filed October 29, 1913, page 1, line 58: "transfer of energy from the wing circuit to the grid circuit, thereby reinforcing the high frequency oscillations in the grid circuit"
- ↑ Patent US1330471 : High-Frequency Signaling. Registered November 29, 1915 , published February 10, 1920 , Applicant: Western Electric Company, Inventor: Burton W. Kendall.
- ↑ Johannes Wiesent: Wireless telegraphy. Verlag von Ferdinand Enke, 1919, p. 28 Der Schwebungsempfang
- ↑ Kirk A. Kleinschmidt: ARRL Handbook. American Radio Relay League, 1990, ISBN 0-87259-167-0 , pp. 12-7.
- ^ HJ Hicks: Principles and Practice of Radio Servicing. McGraw-Hill Book Company, 1943, Second Edition, p. 176.
- ↑ Heinz Richter: New Bastelbuch for radio and electronics. Franckh'sche Verlagsbuchhandlung, Stuttgart 1957, pages 23, 24 and 25.
- ↑ Charles Kitchin: N1TEV. Regenerative Receivers Past and Present. Communications Quarterly, Fall 1995, "Bipolar detectors ... the devices I've built never seem to work as well as any of my JFET designs"
- ↑ Link to: Hagen Jakubaschk : Radio tinkering - made easy. Children's book publisher of the GDR, 1964, page 318, fig. 200 (The author describes this circuit on page 319 as reflex audion and as a single circle )