Issue 8 of the Radio Amateur magazine for 1924 was dedicated to Losev's "kristadin". The word "cristadin" was made up of the words "crystal" and "heterodyne", and the "cristadyne effect" was that when a negative bias was applied to the zincite (ZnO) crystal, the crystal began to generate undamped oscillations.
The effect had no theoretical justification. Losev himself believed that the effect was due to the presence of a microscopic "voltage arc" at the point of contact between the zincite crystal and the steel wire.
The discovery of the "cristadyne effect" opened up exciting prospects in radio engineering ...
... but it turned out as always ...
In 1922, Losev demonstrates the results of his research on the use of a crystal detector as a generator of undamped oscillations. In the publication on the topic of the report, schemes of laboratory tests and a mathematical apparatus for processing research material are given. Let me remind you that Oleg at that time was not yet 19 years old.
The figure shows the test circuit of the "cristadin" and its "N-shaped" current-voltage characteristic, typical for tunnel diodes. That Oleg Vladimirovich Losev was the first to put into practice the tunnel effect in semiconductors became clear only after the war. It cannot be said that tunnel diodes are widely used in modern circuitry, but a number of solutions based on them successfully work on microwaves.
A new breakthrough in radio electronics did not happen: all the forces of the industry were then thrown into improving radio tubes. Radio tubes successfully replaced electric machines and arc gaps from transmitting radio equipment. Radios on lamps worked more and more steadily and became cheaper. Therefore, professional radio engineers "kristadin" was then considered as a curiosity: a heterodyne receiver without a lamp, wow!
For radio amateurs, the design of the “cristadin” turned out to be rather complicated: a battery was required to supply a bias voltage to the crystal, it was necessary to make a potentiometer to adjust the bias, it was necessary to make another inductor to search for the generating points of the crystal.
In the NRL, the difficulties of radio amateurs were well understood, so they published a brochure where the design of the “kristadin” and the design of the Shaposhnikov receiver were published together. Radio amateurs first made the Shaposhnikov receiver, and then supplemented it with "kristadin" as a radio signal amplifier or local oscillator.
Some theory
At the time of the publication of the “cristadin” design, all types of radio receivers already existed:
1. Detector radios, including direct amplification receivers.
2. Heterodyne radio receivers (also known as direct conversion receivers).
3. Superheterodyne radio receivers.
4. Regenerative radio receivers, incl. autodynes and synchrodynes.
The simplest of the radio receivers was and remains a detector:
The detector receiver operates extremely simply: when exposed to a negative carrier half-wave selected on the L1C1 circuit, the detector resistance VD1 remains high, and when exposed to a positive one, it decreases, i.e. detector VD1 "opens". When receiving amplitude modulated signals (AM) with the “open” detector VD1, the blocking capacitor C2 is charged, which is discharged through the headphones BF after the detector is “closed”.
The graphs show the process of AM signal demodulation in detector receivers.
The shortcomings of the detector radio receiver are obvious from the description of the principle of its operation: it is not able to receive a signal whose power is not enough to “open” the detector.
To increase the sensitivity, in the input resonant circuits of the detector receivers, "self-induction" coils were actively used, wound "turn by turn" on cardboard sleeves of large diameter with thick copper wire. Such inductors have a high quality factor, i.e. the ratio of reactance to active. This made it possible, when tuning the circuit to resonance, to increase the EMF of the received radio signal.
Another way to increase the sensitivity of a detector radio receiver is to use a local oscillator: the signal of an oscillator tuned to the carrier frequency is "mixed" into the input circuit of the receiver. In this case, the detector is “opened” not by a weak carrier signal, but by a powerful generator signal. Heterodyne reception was discovered even before the invention of radio tubes and crystal detectors and is still used today.
"Kristadin", used as a local oscillator, is indicated in the figure by the letter "a", the letter "b" indicates a conventional detector receiver.
A significant drawback of heterodyne reception was the whistle, which occurs due to the “frequency beats” of the local oscillator and the carrier. This "flaw", by the way, was actively used to receive "by ear" radiotelegraph (CW), when the receiver's local oscillator was tuned in frequency by 600 - 800 Hz from the transmitter frequency and when the key was pressed, a tone signal appeared in the phones.
Another disadvantage of heterodyne reception was the periodic “attenuation” of the signal, noticeable by ear, when the frequencies coincided, but the phases of the local oscillator and carrier signals did not match. The regenerative tube radio receivers (Reinarz receivers) that reigned supreme in the mid-20s were deprived of this shortcoming. With them, too, everything was not easy, but that's another story ...
About "superheterodynes" it should be mentioned that it became economically feasible to produce them only from the mid-30s. Currently, "superheterodynes" are still widely used (unlike "regenerators" and "detectors"), but are being actively replaced by heterodyne devices with software signal processing (SDR).
Who is Mr Losev?
The story of the appearance of Oleg Losev in the Nizhny Novgorod radio laboratory began back in Tver, where, after listening to a lecture by the head of the Tver receiving radio station, staff captain Leshchinsky, the young man lights up the radio.
After graduating from a real school, a young man goes to enter the Moscow Institute of Communications, but somehow arrives in Nizhny Novgorod and tries to get a job at the NRL, where he is taken by courier. There is not enough money, he has to sleep in the NRL on the landing, but this is not an obstacle for Oleg. He conducts research on physical processes in crystal detectors.
Colleagues believed that prof. VC. Lebedinsky, whom he met back in Tver. The professor singled out Losev and liked to talk with him on research topics. Vladimir Konstantinovich was invariably benevolent, tactful and gave a lot of advice disguised as questions.
Oleg Vladimirovich Losev devoted his whole life to science. I preferred to work alone. Published without co-authors. Was not happy in marriage. In 1928 he moved to Leningrad. Worked at CRL. Worked with ac. Ioffe. Became Ph.D. "on the basis of work." He died in 1942 in besieged Leningrad.
From the collection "Nizhny Novgorod Pioneers of Soviet Radio Engineering" about Losev's "kristadin":
Oleg Vladimirovich's research in its content at first had a technical and even amateur radio character, but it was with them that he won world fame by discovering in a zincite (mineral zinc oxide) detector with a steel tip the ability to excite undamped oscillations in radio circuits. This principle formed the basis of a tubeless radio with signal amplification, which has the properties of a tube. In 1922, it was called "cristadin" (crystalline heterodyne) abroad.
Not limiting himself to the discovery of this phenomenon and the constructive development of the receiver, the author develops a method for artificially refining second-rate zincite crystals (by melting them in an electric arc), and also seeks a simplified method for finding active points on the crystal surface for touching the tip, which provided excitation of vibrations.
The problems that arose in this case did not have a trivial solution; it was necessary to conduct research in as yet undeveloped areas of physics; amateur radio failures stimulated physics research. It was completely applied physics. The simplest explanation for the oscillating phenomenon then looming was its relation to the thermal coefficient of resistance of the zincite detector, which, as expected, turned out to be negative.
Used sources:
1. Losev O.V. At the origins of semiconductor technology. Selected works - L .: Nauka, 1972
2. "Radio amateur", 1924, No. 8
3. Ostroumov B.A. Nizhny Novgorod pioneers of Soviet radio engineering - L .: Nauka, 1966
4.
5. Polyakov V.T. Radio technology. Simple receivers of AM signals - M .: DMK Press, 2001
Source: habr.com