This curve shows that large variation of output voltage results into minor variation in input voltage. [17][56] Difference between 802.11 standards viz.11-a,11-b,11-g and 11-n Since the detector would only function when the contact was made at certain spots on the crystal surface, the contact point was almost always made adjustable. [74] The vacuum tubes used as mixers at lower frequencies in superheterodyne receivers could not function at microwave frequencies due to excessive capacitance. Traditionally, in a crystal detector radio tuned circuits, a mechanical type variable capacitor is used. [31] The goal of researchers was to find rectifying crystals that were less fragile and sensitive to vibration than galena and pyrite. Discovery of the light emitting diode (LED), Development of the theory of semiconductor rectification. — Shortwaue Crystal Radio by Dave Schmarder A miniature, but selective and high performance CRYSTAL RADIO KIT [17], So during the 1920s vacuum tube receivers replaced crystal radios in all except poor households. and L. W. Austin invented a silicon–tellurium detector. [8][11] In 1907 he formed a company to manufacture his detectors, Wireless Specialty Products Co., and the silicon detector was the first crystal detector to be sold commercially. A breakthrough came when it was realized that the rectifying action of crystalline semiconductors was not due to the crystal alone but to the presence of impurity atoms in the crystal lattice. at Siemens & Halske research laboratory in Germany and Nevill Mott[76] [41] Instead spark gap transmitters transmitted information by wireless telegraphy; the user turned the transmitter on and off rapidly by tapping on a telegraph key, producing pulses of radio waves which spelled out text messages in Morse code. A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio.It uses only the power of the received radio signal to produce sound, needing no external power. [5] Researchers investigating the effect of radio waves on various types of "imperfect" contacts to develop better coherers, invented crystal detectors. [17][40] These transmitters were unable to produce the continuous sinusoidal waves which are used to transmit audio (sound) in modern AM or FM radio transmission. The coherer was used as detector for the first 10 years, until around 1906. With an intact crystal, the DC voltage at the base of the transistor T2 is high enough to cause the transistor … [44] The 1918 edition of the US Navy's manual of radio stated: ", The 1920 "British Admiralty Handbook of Wireless Telegraphy" stated that: ", Schottky, W. "Halbleitertheorie der Sperrsschicht." Some semiconductor diodes have a property called negative resistance which means the current through them decreases as the voltage increases over a part of their I–V curve. [8] [70] Crystal radio sets Crystal radio circuits Crystal detector Crystal types Crystal radio components In the heyday of the crystal radio set there were many stockists supplying a wide variety of the different components and other parts needed to make or build one of these sets. For modern crystal detectors, see, Circuit of a simple crystal radio. This law has been mathematically explained in the below section. The antenna absorbs transmitted radio signals (b) which flow to ground via the other components. The galena detector is inside the horn antenna. The received sound is best obtained over a crystal earphone. Semiconductor Devices: Pioneering Papers. Pickard, an engineer with the American Wireless Telephone and Telegraph Co. invented the rectifying contact detector,[49][50] discovering rectification of radio waves in 1902 while experimenting with a coherer detector consisting of a steel needle resting across two carbon blocks. = a1*(A*cos(w*t)) + a2* (A2/2) *(1+cos(2*w*t)) ... Equation-4. The German word halbleiter, translated into English as "semiconductor", was first used in 1911 to describe substances whose conductivity fell between conductors and insulators, such as the crystals in crystal detectors. In contrast, an Anger scintillation camera is stationary, with a number of photomultiplier tubes receiving gamma rays through a collimator with many holes, and an electronic data-processing circuit. How to build Crystal tester circuit. While investigating crystal detectors in the mid-1920s at Nizhny Novgorod, Oleg Losev independently discovered that biased carborundum and zincite junctions emitted light. Circular Cavity Resonator Calculator Germanium diodes are more sensitive than silicon diodes as detectors, because germanium has a lower forward voltage drop than silicon (0.4 vs 0.7 volts). [7] Crystals were first used as radio wave detectors in 1894 by Jagadish Chandra Bose in his microwave experiments. Here’s my first version of the crystal tester circuit, actually a meliorated adaption of a timeworn circuit I took from the net. Crystal radios had no amplifying components to increase the loudness of the radio signal; the sound power produced by the earphone came solely from the radio waves of the radio station being received, intercepted by the antenna. [63][65][68] Therefore, the sensitivity of the detector was a major factor determining the sensitivity and reception range of the receiver, motivating much research into finding sensitive detectors. Abstract in English as "Semiconductor Theory of the Blocking Layer" in Sze, S.M. Therefore, carborundum detectors were used in shipboard wireless stations where waves caused the floor to rock, and military stations where gunfire was expected.[5][22]. The crystal detector is widely used in Rf and microwave field due to their sensitivity and simple design. For those of you who would like to eliminate this mechanical component, here is a modern version of the classic detector set. [3][5][23][26] The contact between the tip of the wire and the surface of the crystal formed a crude unstable point-contact metal–semiconductor junction, forming a Schottky barrier diode. Dissatisfied with this detector, around 1897 Bose measured the change in resistivity of dozens of metals and metal compounds exposed to microwaves. – The instrument measures relative power up to 200 mW and has a BNC female connector for the In 1907–1909, George Washington Pierce at Harvard conducted research into how crystal detectors worked. They noticed that when their detectors were biased with a DC voltage to improve their sensitivity, they would sometimes break into spontaneous oscillations. i = a0 + a1*v + a2*v2 + a3*v3 ...Equation-1 [8][10] This is often considered the first patent on a semiconductor device. [18][53] Until the triode vacuum tube began to be used during World War 1, crystals were the best radio reception technology, used in sophisticated receivers in wireless telegraphy stations, as well as in homemade crystal radios. Losev died in World War 2. Losev did extensive research into the mechanism of light emission. ", Sarkar, Tapan K.; Sengupta, Dipak L. "An appreciation of J. C. Bose's pioneering work in millimeter and microwaves" in, Some biographical information on General Henry H.C. Dunwoody is available at. You may use the stop function to get the relevant data. Bluetooth vs zigbee [22][26] In Pickard's commercial detector (see picture), multiple zincite crystals were mounted in a fusible alloy in a round cup (on right), while the chalcopyrite crystal was mounted in a cup on an adjustable arm facing it (on left). a2*A2/2, which flows through mA meter. So it can be soldered onto the perforated board, easy to save money and time. 4. Glancing over at my circuit, I discovered to my great surprise that instead of cutting out two of the cells I had cut out all three; so, therefore, the telephone diaphragm was being operated solely by the energy of the receiver signals. This would have the advantage of using a quiet place RF-wise for the detector. [63] However his achievements were overlooked because of the success of vacuum tubes. The silicon detector had some of the same advantages as carborundum; its firm contact could not be jarred loose by vibration, so it was used in commercial and military radiotelegraphy stations. The birth of quantum mechanics in the 1920s was the necessary foundation for the development of semiconductor physics in the 1930s, during which physicists arrived at an understanding of how the crystal detector worked. The crystal detector was the most successful of many detector devices invented during this era. This radio, as shown on Figure 1, uses a varactor diode instead of the usual mechanical rotary device. Hence current is proportional to the applied voltage. Crystal Set c 0m P/N IN34 Detector un ing oil Capac i looopF Tap Earth Terminal Coi': 1.6 inch o.d. The figure-1 depicts crystal detector circuit with its characteristics. [1][5] Before a radio wave was applied, this device had a high electrical resistance, in the megohm range. Pickard invented his silicon detector in 1906. This allows a diode, normally a passive device, to function as an amplifier or oscillator. [8][74] Hans Hollmann in Germany made the same discovery. [5] The wire was suspended from a moveable arm and was dragged across the crystal face by the user until the device began functioning. 381, List of historic technological nomenclature, "Carborundum and silicon detectors for wireless telegraphy", "Ueber die Stromleitung durch Schwefelmetalle", "Crystal rectifiers for electric currents and electric oscillations, Part 1: Carborundum", "The work of Jagadish Chandra Bose: 100 years of mm-wave research", "The Discovery of the Oscillating Crystal", "Section 14 – Expanded Audio and Vacuum Tube Development (1917–1924)", "The Crystal as a Generator and Amplifier", Lee, Thomas H. (2004) The Design of CMOS Radio-Frequency Integrated Circuits, 2nd Ed., p. 20, "The life and times of the LED – a 100-year history", "1931: "The Theory Of Electronic Semi-Conductors" is Published",, Creative Commons Attribution-ShareAlike License, This page was last edited on 16 December 2020, at 20:39. During the first three decades of radio, from 1888 to 1918, called the wireless telegraphy or "spark" era, primitive radio transmitters called spark gap transmitters were used, which generated radio waves by an electric spark. His technology was dubbed "Crystodyne" by science publisher Hugo Gernsback[64] one of the few people in the West who paid attention to it. [8] By about 1942 point-contact silicon crystal detectors for radar receivers such as the 1N21 and 1N23 were being mass-produced, consisting of a slice of boron-doped silicon crystal with a tungsten wire point pressed firmly against it. A GDO tuned to 12 MHz acting as signal generator, placed within about 5 cm of the detector. at Bristol University, UK. Pierce originated the name crystal rectifier. Difference between TDD and FDD Crystal earphones can be used. At that time you could get a chunk of silicon... put a cat whisker down on one spot, and it would be very active and rectify very well in one direction. Selective, Fixed Detector Crystal Set. This was before radio waves had been discovered, and Braun did not apply these devices practically but was interested in the nonlinear current–voltage characteristic that these sulfides exhibited. [2][3] It was the first type of semiconductor diode,[2][4] and one of the first semiconductor electronic devices. [22], Another category was detectors which used two different crystals with their surfaces touching, forming a crystal-to-crystal contact. Like other scientists since Hertz, Bose was investigating the similarity between radio waves and light by duplicating classic optics experiments with radio waves. Naturwissenschaften Vol. Another desired property was tolerance of high currents; many crystals would become insensitive when subjected to discharges of atmospheric electricity from the outdoor wire antenna, or current from the powerful spark transmitter leaking into the receiver. [5][22] The device was very sensitive to the exact geometry and pressure of contact between wire and crystal, and the contact could be disrupted by the slightest vibration. square of amplitude A of microwave voltage. If the crystal being tested is intact, the circuit oscillates. Crystal Radio Receiver basics and circuit, difference between FDM and OFDM The temperamental, unreliable action of the crystal detector had always been a barrier to its acceptance as a standard component in commercial radio equipment[1] and was one reason for its rapid replacement. [22][26][36][35] The voltage was adjusted with the potentiometer until the sound was loudest in the earphone. Bose's millimeter wave spectrometer, 1897. [56] Building a crystal set remained a popular educational project to introduce people to radio, used by organizations like the Boy Scouts. This article is about historical crystal detectors. [26][37] The surface of the silicon was usually ground flat and polished. Thirty years after these discoveries, after Bose's experiments, Braun began experimenting with his crystalline contacts as radio wave detectors. Following are the applications of crystal detector. It consists of just four components: inductor and variable capacitor (to form the tuned circuit); diode (to act as the envelope detector); and headphones. [3] It was not sensitive to vibration and so was used in shipboard wireless stations where the ship was rocked by waves, and military stations where vibration from gunfire could be expected. [65] Nobel Laureate Walter Brattain, coinventor of the transistor, noted:[74]. AM radio broadcasting spontaneously arose around 1920, and radio listening exploded to become a hugely popular pastime. [35] Although Pierce didn't discover the mechanism by which it worked, he did prove that the existing theories were wrong; his oscilloscope waveforms showed there was no phase delay between the voltage and current in the detector, ruling out thermal mechanisms. In the regenerodyne circuit the LO is crystal controlled and fixed frequency, the detector is variable frequency. [65][69] Losev designed practical carborundum electroluminescent lights, but found no one interested in commercially producing these weak light sources. [17][40], The coherer was a very poor detector, motivating much research to find better detectors. Microwave crystal detector uses silicon chip (1/16 inch square) and tungsten whisker wire (3/1000 inch diameter). He wrote to Einstein about it, but did not receive a reply. [12][13] He patented the silicon detector 30 August 1906. • Second component i.e. One crystal was zincite (zinc oxide, ZnO), the other was a copper iron sulfide, either bornite (Cu5FeS4) or chalcopyrite (CuFeS2). [3][5] Since at the time they were developed no one knew how they worked, crystal detectors evolved by trial and error. [59][60][61][62][63] [22], Patented and first manufactured in 1906 by Pickard,[11][35] this was the first type of crystal detector to be commercially produced. • Used as video detector which produces DC output based on input signal frequency (unmodulated or modulated). In 1877 and 1878 he reported further experiments with psilomelane, (Ba,H2O)2Mn5O10. The theory of rectification in a metal-semiconductor junction, the type used in a cat whisker detector, was developed in 1938 independently by Walter Schottky[75] A generalised crystal radio circuit is shown in Fig. This version was deliberately made to look and function like a human eyeball, with a lens focusing millimeter waves on the galena contact. [5][7][14] Therefore, a usable point of contact had to be found by trial and error before each use. Braun did investigations which ruled out several possible causes of asymmetric conduction, such as electrolytic action and some types of thermoelectric effects.[44]. i = a1*(A*cos(w*t)) + a2*(A*cos(w*t))2 CRYSTAL SET. Difference between SISO and MIMO [3][22] Crystals that required a light pressure like galena were used with the wire cat whisker contact; silicon was used with a heavier point contact, while silicon carbide (carborundum) could tolerate the heaviest pressure. Marconi used carborundum detectors beginning around 1907 in his first commercial transatlantic wireless link between Newfoundland, Canada and Clifton, Ireland. Also in 1906 Henry Harrison Chase Dunwoody,[51] [74] This for the first time created semiconductor junctions with reliable, repeatable characteristics, allowing scientists to test their theories, and later making manufacture of modern diodes possible. The 8472B crystal detector is a 50 W (nominal) device designed for measurement use in coaxial systems. Although the zincite-chalcopyrite "Perikon" was the most widely used crystal-to-crystal detector, other crystal pairs were also used. Figure 1: circuit diagram of the RF diode detector with audio amplifier. This curve is approximated by Taylor series as shown by following equation-1. The crystal earpiece has such high impedence that it presents virtually no load to the CD4024. Graphing the current as a function of voltage across a contact made by a piece of mineral touched by a wire cat whisker, he found the result was a line that was flat for current in one direction but curved upward for current in the other direction, instead of a straight line, showing that these substances did not obey Ohm's law. At the time scientists thought that radio wave detectors functioned by some mechanism analogous to the way the eye detected light, and Bose found his detector was also sensitive to visible light and ultraviolet, leading him to call it an artificial retina. Greenleaf Whittier Pickard may be the person most responsible for making the crystal detector a practical device. The Felix Bloch and Rudolf Peierls around 1930 applied quantum mechanics to create a theory of how electrons move through a crystal. [24][25] The carborundum junction saw some use as a detector in early vacuum tube radios because it was more sensitive than the triode grid-leak detector. [17] But lacking amplification, crystal radios had to be listened to with earphones, and could only receive nearby local stations. Goofus uses waveg… [72] The maddeningly variable activity of different pieces of crystal when used in a detector, and the presence of "active sites" on the surface, was due to natural variations in the concentration of these impurities throughout the crystal. The first person to exploit negative resistance practically was self-taught Russian physicist Oleg Losev, who devoted his career to the study of crystal detectors. A crystal detector is an[1] electronic component used in some early 20th century radio receivers that consists of a piece of crystalline mineral which rectifies the alternating current radio signal and was employed as a detector (demodulator) to extract the audio modulation to produce the sound in the earphones. This refers to higher sensitivity of the crystal detector. OFDM vs OFDMA This crystal size limits power handling capabiliy of crystal detector to about 100 mWatt. Until the triode vacuum tube began to be used around World War 1, radio receivers had no amplification and were powered only by the radio waves picked up by their antennae. The first person to use crystals for radio wave detection was Indian physicist Jagadish Chandra Bose of the University of Calcutta in his landmark 60 GHz microwave optics experiments from 1894 to 1900. [5][26] The "Perikon" detector, invented 1908 by Pickard[38] was the most common. [73] In 1931, Alan Wilson created quantum band theory which explains the electrical conductivity of solids. It is the test circuit. The amplifier must have a high impedance input, as well as phono or guitar. Its function was to act as a demodulator, rectifying the radio signal, converting it from alternating current to a pulsing direct current, to extract the audio signal (modulation) from the radio frequency carrier wave. This can be a detector circuit of a 2 circuit receiver. crystal detector characteristics and mathematical equations. although at the microwave frequencies he used these detectors did not function as rectifying semiconductor diodes like later crystal detectors, but as a thermal detector called a bolometer. Difference between SC-FDMA and OFDM Around 1907 crystal detectors replaced the coherer and electrolytic detector to become the most widely used form of radio detector. He patented the detector 30 September 1901. This results into following equation. Module 2. Using Crystal Earphone. Instead spark gap transmitters transmitted information by wireless telegraphy; the user turned the transmitter on and off rapidly by tapp… Long before Beavis and Butthead provided wholesome entertainment, Goofus and Gallant were teamed in a magazine called Children's Highlights that your parents would subscribe to if they were afraid that you were in danger of being a juvenile delinquent. 3.8 TV Cas- cade Sync Clipper. CDMA vs GSM RP represents the losses in coil L and tuner capacitor C1 [2] In 1906 he obtained a German patent on a galena cat whisker detector, but was too late to obtain patents in other countries. During the next four years, Pickard conducted an exhaustive search to find which substances formed the most sensitive detecting contacts, eventually testing thousands of minerals,[8] and discovered about 250 rectifying crystals. Only certain sites on the crystal surface functioned as rectifying junctions. [28][29] The spark produced by the buzzer's contacts functioned as a weak radio transmitter whose radio waves could be received by the detector, so when a rectifying spot had been found on the crystal the buzz could be heard in the earphones, at which time the buzzer was turned off. 3.10 TV Vertical Pulse Separator. [3] Therefore, it was the most common type used in commercial radiotelegraphy stations. Crystal oscillator and other types of oscillators What is Quartz Crystal a2* (A2/2)*cos(2*t) flows through capacitor (C). [47] He first used a coherer consisting of a steel spring pressing against a metal surface with a current passing through it. The circuit shown below shows the most basic form of crystal radio circuit. [36] Carborundum, an artificial product of electric furnaces produced in 1893, required a heavier pressure than the cat whisker contact. Carborundum proved to be the best of these;[36] it could rectify when clamped firmly between flat contacts. The curve is square law in nature and hence output voltage is proportional to square of input voltage.This law has been mathematically explained in the below section.This curve shows that large variation of output voltage results into minor variation in input voltage.This refers to higher sensitivity of the crystal detector.This curve is approximated by Taylor series as shown by following equation-1. Crystal radio detector biasing. Phones 3-22 47k Ohm Tunes 5-7 mhz anmox. [12][13][50] On 29 May 1902 he was operating this device, listening to a radiotelegraphy station. [22] In a crystal radio, the user would tune the radio to a strong local station if possible and then adjust the cat whisker until the station or radio noise (a static hissing noise) was heard in the radio's earphones. Short circuit description: Diodes D1 and D2 rectify the RF input signal. "...crystal detectors have been used [in receivers] in greater numbers than any other [type of detector] since about 1907. Then press S1 to see the LED1 brightness. The given circuit, designed to work from 5-12V dc supply input, can be used to evaluate standard crystals having got frequency around 20MHz. [13][59] [1][5][6], The "asymmetric conduction" of electric current across electrical contacts between a crystal and a metal was discovered in 1874 by Karl Ferdinand Braun. In 1949 at Bell Labs William Shockley derived the Shockley diode equation which gives the nonlinear exponential current–voltage curve of a crystal detector, observed by scientists since Braun and Bose, which is responsible for rectification .[72]. [1] The device which did this was called a detector. Vacuum tubes temporarily put an end to crystal detector research. [8] Such point-contact diodes are still being manufactured, and may be considered the first modern diodes. After ten years he abandoned research into this technology and it was forgotten.[63]. Coherers required an external current source to operate, so he had the coherer and telephone earphone connected in series with a 3 cell battery to provide power to operate the earphone. The circuit is simple and easy to build, here is the schematic diagram: This crystal tester circuit use only two transistor, the first transistor is used as an oscillator, and the second one is employed as the detector. This amplifier can exhibit negative resistance for low settings of the 500 ohm pot which results in extra gain or even oscillation. Features – The instrument converts RF power levels applied to the 50 W input connector into proportional values of DC voltage. 4. This circuit, whilst easy to make did not provide any matching for the antenna and therefore the performance would not have been as good as some. Tuned Crystal-Type Signal Tracer. [12] Long distance radio communication depended on high power transmitters (up to 1 MW), huge wire antennas, and a receiver with a sensitive detector.[12]. He realized that amplifying crystals could be an alternative to the fragile, expensive, energy-wasting vacuum tube. [12][44] Using an oscilloscope made with Braun's new cathode ray tube, he produced the first pictures of the waveforms in a working detector, proving that it did rectify the radio wave. CHAPTER IV Experimental Applications 4.1 Amplitude Modulator. 23awg Wre Antenna: 5 turns Detector: 30 turns tapped at 20 turns. [12] Silicon required more pressure than the cat whisker contact, although not as much as carborundum. The circuit below is a simple but effective amplifier which will give surprising performance improvement. After the war, germanium diodes replaced galena cat whisker detectors in the few crystal radios being made. The cat whisker contact did not require adjustment, and these were sealed units. Besides having a longer transmission range, these transmitters could be modulated with an audio signal to transmit sound by amplitude modulation (AM). [28] This required some skill and a lot of patience. These slowly replaced the old damped wave spark transmitters. crystal oscillator vs frequency synthesizer In 1922 working at the new Nizhny Novgorod Radio Laboratory he discovered negative resistance in biased zincite (zinc oxide) point contact junctions. [5], Guglielmo Marconi developed the first practical wireless telegraphy transmitters and receivers in 1896, and radio began to be used for communication around 1899. AT cut vs SC Cut Quartz crystal The chalcopyrite crystal was moved forward until it touched the surface of one of the zincite crystals. This detector was also sometimes used with a small forward bias voltage of around 0.2V from a battery to make it more sensitive.[22][36]. Cavity resonator basics It was found that, unlike the coherer, the rectifying action of the crystal detector allowed it to demodulate an AM radio signal, producing audio (sound). and the 16 papers he published on LEDs between 1924 and 1930 constitute a comprehensive study of this device. • Used in RF mixers for super heterodyne circuit. However he just published a brief two paragraph note about it and did no further research.[66]. [2][8][9] Bose first patented a crystal detector in 1901. [36], Silicon carbide is a semiconductor with a wide band gap of 3 eV, so to make the detector more sensitive a forward bias voltage of several volts was usually applied across the junction by a battery and potentiometer. In addition to its main use in crystal radios, crystal detectors were also used as radio wave detectors in scientific experiments, in which the DC output current of the detector was registered by a sensitive galvanometer, and in test instruments such as wavemeters used to calibrate the frequency of radio transmitters.[21]. The crystal detector, Pictorial diagram from 1922 showing the circuit of a cat whisker crystal radio. A crystal radio uses only tuned circuits to select the stations, and a crystal detector to rectify the radio station's signal to enable it to be heard with a set of headphones. When creating a Crystal tester circuit is complete. Resonator basics and Resonator types The semiconductor chip and metal whisker are two essential parts of a crystal detector. A second Pierce crystal oscillator acting as BFO, placed within about 5 cm of the detector (no electrical connection). Circuit diagram 1 Circuit diagram of the crystal receiver, which we are going to design for maximum sensitivity at weak signals. The detector consists of a special center-tapped transformer feeding two diodes in a full wave DC rectifier circuit. When a sensitive spot was located, the arm was locked in place with the setscrew. It consisted of a pea-size piece of crystalline mineral in a metal holder, with its surface touched by a fine metal wire or needle (the "cat whisker"). Here crystal behaves as simple resistor with negligible amount of He used biased negative resistance crystal junctions to build solid-state amplifiers, oscillators, and amplifying and regenerative radio receivers, 25 years before the invention of the transistor. Figure 1-4 is the circuit of a video detector employing the This circuit will be of interest to builders of home-made television receivers who wish to reduce the amount of tube space on the chassi- while at the same time taking advantage of the additional improvements offered by the crystal detector. 1.6 CRYSTAL DC RESTORER FOR TELEVISION. i = a1*(A*cos(w*t)) Semiconductor devices like the crystal detector work by quantum mechanical principles; their operation cannot be explained by classical physics. and Pickard. Bose's galena detector from his 1901 patent. [5][12][13] In 1906 he obtained a sample of fused silicon, an artificial product recently synthesized in electric furnaces, and it outperformed all other substances. Crystal radio with detector diode bias. [72][73][74] Mott received the 1977 Nobel Prize in Physics. Annoyed by background "frying" noise caused by the current through the carbon, he reached over to cut two of the battery cells out of the circuit to reduce the current[12][13], The frying ceased, and the signals, though much weakened, became materially clearer through being freed of their background of microphonic noise.