Loose Contact Devices

Updated June 2019

Loose Contact Devices or the Loose Contact Principle  or Imperfect Contact – yes, you got it – permanently arcing contacts have been a mystery to science since at least 1879 when David Hughes first studied them… AND YET WE USE THEM EVERY DAY.

David Hughes’ carbon microphone, the first wireless detector, was debunked by the Royal Society – would you believe? See below

Note: any reference to radio or wireless on this page refers to Morse code transmissions and not audio (speech) transmissions unless more recent technology is discussed.

David Edward Hughes

When I started to write this page I had no idea where it would lead. I had no idea that the microphone used in the first wireless transmission/reception would lead to the diode the transistor, the memristor and the scanning tunnelling microscope (STM). In fact I found only one other person who had followed the same path.


The microphone is so commonly used  that few of us ever give it a second thought. Microphones are essential for the operation of most of our modern technology (I must admit that its importance never occurred to me until I started researching this page). It was David Hughes (above) who found that a *carbon microphone* could not only transmit audible sounds but that it could also be used to detect wireless signals. As a direct result it was he who made the first transmission and reception of a wireless signal in 1879. The rest is over a hundred years of history; the carbon mic became the coherer and the coherer was replaced by the cat’s-whisker diode for crystal radio. Followed by the triode vacuum tube radio that was eventually replaced by the transistor. All of the above were what’s called Loose Contact Devices and each was dependant upon the one that went before it. No one, not science, not engineering, has ever had a complete or even plausible explanation as to how or why any of them work. Science will tell you what they do but has no explanation as to why they do it.

The Carbon Button Microphone and possibly the telegraph key were the first ‘known’ Loose Contact Devices. Something never mentioned by the mainstream.

An early telephone with carbon mic of the type used in the Bell system. The name Bell is Alexander G Bell, the same company as Bell Labs (or Hells Bells) of transistor fame, can be found lower down this page.

Early Telephone – Alexander Graham Bell
Wiki misinformation: Alexander Graham Bell (1847 – 1922) was a Scottish-born scientist, inventor, engineer, and innovator who is credited with patenting the first practical telephone and founding the American Telephone and Telegraph Company (AT&T) in 1885.

Bell was a teacher of the deaf, not an academic scientist nor was he a qualified engineer. Wiki editors think that being able to use the imagination has to be something to do with a scientific qualification – when it suits the purpose.

moah.org is better – they almost get it right: While working on devices to help the hearing-impaired in 1876, Alexander Graham Bell developed a simple combination receiver (earphone) and transmitter (microphone) using a bar magnet, a coil of fine wire and a thin metal disk (diaphragm). Bell’s device worked both as a microphone and an earphone….  Unfortunately, the sound was quite weak and could not serve as the basis of a commercial telephone. However, the (later) receiver portion of his device (carbon microphone) worked very well and was used in virtually all commercial telephones around the world.

The missing element was a better transmitter or microphone. A device that would generate a strong electrical equivalent of the voice would complete a telephone that could be used for long distance communication. This device, the carbon microphone, was invented by both Edison and Francis Blake in 1877 and patented by Edison.

The identity of the inventor is still a cause for much controversy. It may have been invented by David Hughes, who appears to have invented things to entertain himself rather than for commercial purposes.


Emile Berliner was credited with inventing the carbon-button microphone patented by him on the 16-12-1879. Alexander Graham Bell was so impressed with the microphone that he bought the rights for $50,000 (1.1 million dollars in today’s money), so he could use it in his telephone prototypes.

Microphone Wars – Will the Inventor Step Forward?

Berliner called his microphone a “loose-contact transmitter” because it was composed of two electrical contacts separated by a thin layer of carbon. Thomas Edison claimed that the patent should be his and a legal challenge ensued that ruled in Edison’s favour. In fact neither of them could claim credit as the ‘carbon button mic’ had been known and demonstrated for some time before either had claimed it. The ‘Loose Contact’ description seems to have been conveniently forgotten by the mainstream and such devices became unclassified.

1927 The Carbon Microphone is an amplifier

Carbon Button Microphone used as an amplifier. Can someone explain how a carbon mic amplifies?  http://onetuberadio.com/2017/03/20/carbon-button-microphone-amplifier/

Wiki: Carbon microphones can be used as amplifiers. This capability was used in early telephone repeaters, making long distance phone calls possible in the era before vacuum tube amplifiers. In these repeaters, a magnetic telephone receiver (an electrical-to-mechanical transducer) was mechanically coupled to a carbon microphone. Because a carbon microphone works by varying a current passed through it, instead of generating a signal voltage as with most other microphone types, this arrangement could be used to boost weak signals and send them down the line. These amplifiers were mostly abandoned with the development of vacuum tubes, which offered higher gain and better sound quality. Even after vacuum tubes were in common use, carbon amplifiers continued to be used during the 1930s in portable audio equipment such as hearing aids. The Western Electric 65A carbon amplifier was 1.2″ in diameter and 0.4″ high and weighed less than 1.4 ounces. Such carbon amplifiers did not require the heavy bulky batteries and power supplies used by vacuum tube amplifiers. By the 1950s, carbon amplifiers for hearing aids had been replaced by miniature vacuum tubes (only to be shortly after replaced by transistors). However, carbon amplifiers are still being produced and sold.

Yes, that’s all very good but how did it amplify? You see the problem?

Below someone has built a recent version – note the reference to “working like a transistor”:

The Beam Amplifier

A beam Amplifier – with a balanced steel beam – The carbon rod is on the right

The theory behind a carbon beam amplifier is straight forward, a rounded carbon rod supported on the end of a balanced beam rests lightly on a moving diaphragm and as the diaphragm moves the resistance changes. In doing so, it varies the current flowing through it. Like the transistor it uses a relatively small current to control a larger one.
Read it all here: http://makearadio.com/visitors/nick-carbon-amplifier.php

The beam amplifier in the above instance is a modern experimental version of the original carbon microphone used as an amplifier. This is just the first of a catalogue of unusual properties that loose contact devices display. There are more references below to the coherer/microphone working in the same way as a transistor.

David Edward Hughes

The carbon microphone becomes a coherer (wireless detector)

Carbon pieces in a glass tube initially used in D E Hughes’ microphone, he also used it as a radio frequency detector (coherer) in his wireless experiments.

In 1879 David Hughes, like many others in his day, was experimenting using a Bell telephone (that had a carbon button microphone) He found that although there was no connection between the two, it was reacting to another piece of equipment that was sparking. He was listening to the sparks via radio waves, or wireless as it was know in the early days. Hughes seems to have come across the phenomenon of wireless radio waves nine years before they were ‘proven’ to exist by Heinrich Hertz in 1888.
See also:

Another Hughes Carbon Microphone – mounted on a sounding board

Anyone with only a smattering of radio knowledge will know that radio frequency signals cannot be heard through an electromagnetic (dynamic) earphone or speaker alone. It’s a type of earphone and loud-speaker used up-until the present day. All that is heard is a hum, but here was Hughes listening to sparks. A coherer (See below) was normally required to make the sound audible to the earphone, but this was before anyone knew anything about wireless. It transpired that Hughes was listening through a Bell telephone that had a carbon microphone and an electromagnetic earphone. The carbon mic was acting as if it were a coherer (wireless detector) although such things were not understood.

Hughes carbon microphones. (top) Vertical carbon rod (A) suspended by its pointed ends (bottom) Much Much like the “Beam Amplifier” above. Carbon rod resting on carbon blocks. Sensitivity can be adjusted by the spring (S) Thanks to Wiki

Hughes used a modified clockwork driven spark gap transmitter and a modified version of his Bell telephone microphone, built into a portable receiver in order to continue his experiments. He would leave his transmitter running some Morse code-like sounds and walk around London with his portable receiver – the first radio transmission and reception.

Hughes clockwork actuated spark transmitter

Below is a later coherer that is not used as a microphone but just to detect wireless waves.
Above is a typical (non-microphone) coherer of the day consisting of an evacuated glass tube with two electrodes (P) spaced a few millimetres apart, with loose metal filings or carbon granules in the space between. This needed mechanical tapping to de-cohere or separate the particles.

citizendium.org Coherer: Although the filings coherer was the best known version, there was also significant investigation and development of other materials and coherer designs. A variety of alternatives used electrically conducting materials in various light-contact configurations, including stacking steel balls, using a steel needle with each end resting on a carbon block, a metal tripod sitting lightly on a flat metal plate, and a rotating wheel, slightly immersed in liquid mercury that contained a floating, insulating wax film. In some of the later designs, the coherer was self-restoring — instead of having to be physically jarred to be de-cohered, as soon as the intermittent signal from the transmitter ceased, the coherer automatically returned to its normal state.


The Royal Society hand-waves away pre-Hertzian radio wave detection
Some background on the times

Wiki: On February 20, 1880 he (Hughes) demonstrated his technology to representatives of the Royal Society including Thomas Henry Huxley, Sir George Gabriel Stokes, and William Spottiswoode, then president of the Society. Stokes was convinced the phenomenon Hughes was demonstrating was merely electromagnetic induction, not a type of transmission through the air.

Hughes was not a physicist and seems to have accepted Stokes observations and did not pursue the experiments any further. A connection with Hughes phenomenon and radio waves seems to show up 4 years after Heinrich Hertz’s 1888 proof of their existence when Sir William Crookes mentioned in his 1892 Fortnightly Review article on Some Possibilities of Electricity that he had already participated in “wireless telegraphy” by an “identical means” to Hertz, a statement showing Crookes was probably another attendee at Hughes’ demonstration. (Ed: There was likely more than one demonstration)

(Note: The phenomenon on which the coherer is based was discovered around the mid 1800’s  by a number of investigators independently prior to Hughes but not for wireless detection – this makes Hughes the first person to observe the transmission of electromagnetic waves using a coherer. Reading the Wiki version, it appears that the Wiki editor was hard pressed to admit that the Royal Society got it wrong and throws in the name ‘William Crookes’ as a diversion (since deleted).  Wiki: “A connection with Hughes phenomenon and radio waves seems to show up 4 years after Heinrich Hertz’s 1888 proof”. This and other remarks makes it appear that the discovery by Hughes was inferior to that of Hertz, by it being 4 years late when he was a decade in advance of Hertz. Also note the grudging respect given to David Hughes’ discovery. Wiki bias is not uncommon.

Alternate version from Hughes’ notebooks: Mr Spottiswoode, President of the Royal Society, Professor Stokes and Prof Huxley, visited me today at half past three p.m. and remained until quarter to 6 p.m., in order to witness my experiments with the Extra Current Thermopile, etc. The experiments were quite successful, and at first they were astonished at the results, but at 5 p.m. Prof Stokes commenced maintaining that the results were not due to conduction but to induction, and that results were then not so remarkable, as he could imagine rapid changes of electric tension by induction…

George Gabriel Stokes

Note: Wiki: Sir George Gabriel Stokes, 1st Baronet, PRS 1819 – 1903), was an Irish physicist and mathematician.
Awards: he became a fellow in 1851, he received the Rumford Medal in 1852 in recognition of his inquiries into the wavelength of light, and later, in 1893, the Copley Medal.

Electromagnetic induction only works when conductors are in close proximity, like the windings of a transformer. George Stokes should have known better as such things were common knowledge among physicists at the time. Are we to believe he knew nothing of the work of Michael Faraday also FRS  (1791-1867). The Huges demonstration was in 1880.
Two years after the death of Davy, in 1831, he (Faraday) began his great series of experiments in which he discovered electromagnetic induction, recording in his laboratory diary on 28 October 1831 he was; “making many experiments with the great magnet of the Royal Society”.
In 1833, Michael Faraday became the first Fullerian Professor of Chemistry at the Royal Institution of Great Britain, a position to which he was appointed for life without the obligation to deliver lectures.
(But George Stokes, physicist had never asked him to explain induction?)

Back to Hughes’ notebooks
: Although I showed several experiments which pointed conclusively to its being conduction, he would not listen, but rather pooh-poohed all the results from that moment. This unpleasant discussion was then kept up by him, the others following suit, until they hardly paid any attention to the experiments, even to the one working through gaspipe in Portland Street to Langham Place on roof. They did not sincerely compliment me at the end on results, seeming all to be very much displeased because I would not give at once my Thermopile to the Royal Society so that others could make their results. I told them that when Prof Hughes made an instrument of research, it was for Prof Hughes’s researches and no one else.

They left very coldly and with none of the enthusiasm with which they commenced the experiments. I am sorry at these results of so much labour but cannot help it. (Geddes, from Hughes’s notebooks) Source: http://blogs.ucl.ac.uk/library-rnid/2013/05/03/the-hughes-microphone-and-a-telephone-for-the-deaf/

Wiki Bias

William Crookes

William Crookes may or may not have been present at the demonstration as inferred by Wiki (and then deleted), there would have likely been more than one, but why single him out? Crookes, a major pioneer of particle physics, radioactivity, who also did all the experiments later used by J J Thomson to ‘discover the electron’, is unpopular with modern science due to his involvement in the paranormal and his not being an academic physicist – he was a chemist. But it was in fact Crookes who brought Hughes’ name to the fore because of his discovery of the first wireless transmissions. In a speech before the Royal Academy in England, William Crookes commented upon electromagnetic waves: “Here is unfolded to us a new and astonishing world, one which is hard to conceive should contain no possibilities of transmitting and receiving intelligence.”










The Royal Society waved-away the discovery of not only wireless transmissions, but (unknown at the time) the coherer wireless detector, crucial to early wireless and delayed the benefits of radio transmissions for a decade. Nothing new there, they do the same thing today. But let us not forget folks, that this was the Royal Society, the veritable creme de la creme on the scientific cake – the best that science had to offer… blind to discovery!


Wiki: The basis for the operation of the coherer is that metal particles cohere (cling together) and conduct electricity much better after being subjected to radio frequency electricity. The radio signal from the antenna was applied directly across the coherer’s electrodes. When the radio signal from a “dot” or “dash” came in, the coherer would become conductive.
(This is not strictly true but it will do for now.)

Wiki: In 1879 the Welsh scientist (he was professor of music) David Edward Hughes found that loose contacts between a carbon rod and two carbon blocks as well as the metallic granules in a microphone he was developing responded to sparks generated in a nearby apparatus. https://en.wikipedia.org/wiki/Coherer#History
(Again Wiki gets it wrong – see below)

The credit for the coherer invention is often given to Frenchman Edouard Branly, but he only confirmed the the observations made previously by Hughes.

Below we have some comments from ‘Wiki Coherer’ The coherer is doing various different operations, although Wiki has nothing to say about that:

Wiki Coherer History- First Use: The coherer was known but not as a detector.
Wiki: “The idea that particles could react to electricity was used in English engineer Samuel Alfred Varley’s 1866 lightning bridge, a lightning arrester attached to telegraph lines consisting of a piece of wood with two metal spikes extending into a chamber. The space was filled with powdered carbon that would not allow the low voltage telegraph signals to pass through  but it would conduct and ground a high voltage lightning strike.”

Temistocle Calzecchi-Onesti
Temistocle Calzecchi Onesti (1853 – 1922)

Temistocle Calzecchi-Onesti of Italy began studying the anomalous change in the resistance of thin metallic films and metal particles at Fermo/Monterubbiano. He found that copper filings between two brass plates would cling together, becoming conductive, when he applied a voltage to them. He also found that other types of metal filings would have the same reaction to electric sparks occurring at a distance, a phenomenon that he thought could be used for detecting lightning strikes.[4] Calzecchi-Onesti’s papers were published in il Nuovo Cimento in 1884, 1885 and 1886. https://www.secret-bases.co.uk/wiki/Coherer (Clinging particles is something of a red herring, as we will see)

Lightening is a spark, bigger but the same as in Hughes experiments.

Wiki Coherer Operation:
The basis for the operation of the coherer is that metal particles cohere (cling together) and conduct electricity much better after being subjected to radio frequency electricity. The radio signal from the antenna was applied directly across the coherer’s electrodes. (Note: Some coherers did not use metal particles)


Tripod coherer, built by Branly in 1902, another imperfect contact type. No carbon or metal particles

Definition of a coherer











merriam-webster.com: Coherer: a radio detector in which an imperfectly conducting contact between pieces of conductive material loosely resting against each other is materially improved in conductance by the passage of high-frequency current.
(Note: Again we see that the coherer of choice is the one with metal particles, because other types of coherer cannot be explained away.)

In the circuit below the coherer seems to be driven (biased) by a low voltage battery.

A Marconi coherer circuit for transmitter and receiver Note the low voltage battery for the coherer circuit when Wiki tells us that the coherer will not conduct low voltages.
Note also that the Marconi circuit is tuned by Nikola Tesla’s patented “Four Tuned Circuits

The coherer changes to low resistivity when there is a high voltage or a radio frequency signal applied…
No one has ever adequately explained how the coherer detects (demodulates) a radio signal.

The Marconi (Ernest Rutherford) magnetic detector needs some explaining, no coherer or crystal detector  http://www.sparkmuseum.com/MAGGIE.HTM

Some documents and video’s – Coherer

Coherers a_review_TOC_Fixed This document tells us the coherer is a MOM diode or MIM transistor and, by only a slightly more circuitous route, it appeared as the forerunner to the STM (Scanning Tunnelling Microscope).
This one is the most interesting as it suggests other theories and applications of the coherer without the usual pseudo-theorising.

The Coherer This is a video that demonstrates how a coherer works but fails to say why it works. All the demonstrations show that the coherer conducts a DC current when a high frequency current is introduced. They do not explain how a modulated low frequency audio signal is extracted from a high frequency (radio frequency) signal.

The Return of the Maggie?
geojohn.org: The Magnetic detector never returned as a radio detector, but it did return, first as a wire voice recorder and later the basis for the tape recorder. Its later incarnations included the “floppy disk” and now as the principle behind the magnetic hard disk that can store hundreds of billions of bytes of digital data inside our personal computers.

J C Bose and his Semiconductor Diode

J C Bose Detector


J C Bose and his Semiconductor Diode

Derived directly from the coherer: “Although it was known that certain substances had rectification properties since Braun 1874 it was not known that these properties included radio frequency detection. To give some idea of the mainstream scientific grasp of the phenomenon, in 1931, physicist Wolfgang Pauli advised that “one shouldn’t work on semiconductors, that is a filthy mess; who knows whether any semiconductors exist.”

Extract from Patent No. 755,840, dated March 29, 1904: “According to another way of carrying the first part of the invention into effect I may dispense with mechanical means for producing recovery of the coherer or detector by using sensitive substances in which the recovery is automatic.

I have discovered that substances of a certain class possess the property of self-recovery—namely, those which give a characteristic curve representing relative resistances. With such substances if the relation between a continuously-increasing electromotive force and the resulting current be represented by a curve (in which the abscissæ represent the impressed electromotive force and the ordinates the corresponding values of the current) it will be found that such a curve will not be straight, but either convex or concave to the axis of electromotive force. On describing such a curve of variation (the electromotive force rising from zero to a maximum and falling back from maximum to zero) it will be found that with certain substances the ascending and descending or outgoing and return curves coincide. I find that such substances exhibit automatic and rapid self-recovery from the effects of Hertzian waves. I have found that by employing any substance of this class as the sensitive substance of coherers or detectors for electrical disturbances, Hertzian waves, light-waves, and other radiations I can dispense with mechanical means for effecting the recovery of the coherer or detector—that is to say, these substances possess the property of rapid self-recovery.

Of the substances which give a characteristic curve, such as just described, some have the property of presenting a decreasing resistance to the passage of the electric current with an increasing impressed electromotive force, while others have the opposite property—namely, that of presenting an increased resistance as the impressed force increases. For simplicity’s sake I will call the substances of the former class “positive” and those of the latter class “negative.” I may according to this part of my invention use either class of substances as the sensitive substance of coherers or detectors. As examples of such substances I will mention galena, tellurium, magnesium; (these substances are positive, in the sense just described, and are self-recovering;) halogenated metals—for example, lead and tin; potassium; allotropic silver—namely, silver in a form such as can be obtained by reducing silver chlorid by zinc or by electrolysis; (these substances are all of the negative class and are all self-recovering.) Or I may use chromium, manganese, or zirconium as the sensitive agents in coherers and detectors. These substances are very sensitive and belong to the positive class, as before defined, but are possibly not self-recovering. They may, however, be used with advantage.

According to my invention I may also use ammonia-vapor or carbonic-acid gas in small proportions to stimulate the action of the sensitive agent in coherers or detectors—that is to say, to increase their sensitiveness, the gas being confined in the tube or chamber with the sensitive agent. The ammonia or carbonic-acid gas may also be used in large proportions to produce a depressing action upon the sensitive agent—that is to say, to reduce the sensitiveness thereof…

Explain how this one works?    http://www.geojohn.org/Radios/MyRadios/Coherer/Coherer.html

A Curious, but Seldom Used Radio Detector
geojohn.org: The De Forest Flame Diode
Around 1903, Dr. Lee De Forest invented and experimented with a flame diode. De Forest was rather impressed with the performance of the flame diode as a radio detector, but he realized it had no real practical application. On the other hand, De Forest claimed that he got the idea for his audion tube (1906) while he was experimenting with ionized gases in a flame acting as a radio detector. In this respect the flame diode was a precursor to the audion tube which was a precursor to the triode tube which was a precursor to the multi-element tubes which made modern electronics possible. 

In this video from the Edison Tech Center the guy is quite confident that he knows how it all works. But Hughes tells us that he used his carbon microphone (above) and he also used beads of carbon as detectors and so this rules-out a magnetic process as suggested.

Memristor Nothing is new, it’s a coherer


The Coherer is the elusive Memristor

The memristor’s electrical resistance is not constant but depends on the history of current that had previously flowed through the device, i.e., its present resistance depends on how much electric charge has flowed in what direction through it in the past; the device remembers its history — the so-called non-volatility property.[2] When the electric power supply is turned off, the memristor remembers its most recent resistance until it is turned on again. https://en.wikipedia.org/wiki/Memristor

This video demonstrates that the Coherer is a Memristor?

ieeexplore.ieee.org: In the current paper, it has been demonstrated through experimental results, historical citations and technical arguments that coherer (including cat’s whisker) is the elusive memristor. The current paper draws parallel between the research pursued by scientists in the field of memristor and that in coherer, around a century back. The paper discusses various important milestones in the research of that era along with memristor research and how the scientific community missed to identify the memristor despite being very close to the discovery. The paper demonstrates that the first radios were made of memristor and provides novel applications of the same.

The coherer is a much maligned and neglected device.

The Spark-gap – another early loose contact device


The spark gap has close ties with loose contact devices, used on the original wireless transmitters by Hughes and by Marconi as we see above and by Hertz who got all the credit (but didn’t want it) and a host of other names. A spark gap is a disruptive discharge device that like a switch causes voltage spikes that are considered to be a nuisance by today’s engineers – electrical interference. Spark gaps are now mainly used as safety devices and few are aware of their usefulness in the past. I had to scour the web to find an engineer who admits to the voltage surge effect caused by switching:

Divyang Singhal, electrical engineer writing on Quora
Answered Mar 22 2016 · Author has 334 answers and 717.5k answer views
As the name suggests, switching means the sudden interruption in any circuit and surges means the over-current spikes that are caused in the circuit.
Combined together, switching surges are the over-current/over-voltage spikes that are experienced in the highly inductive circuits at the time of sudden interruption I.e. switching period.
As the magnetic field about the inductive conductor collapses, a brief very high voltage can be generated at that point. These switching surges can be highly dangerous for the electrical system and thus require proper control and protection devices.https://www.quora.com/What-is-switching-surges

It was this “nuisance” that alerted Hughes to the existence of wireless transmissions. The disruption of electric current by the spark and subsequent oscillations enabled modulated electromagnetic radiation from the original circuit and led to wireless telegraphy.

Semiconductors  – Cat’s Whisker, Crystal Detector and audio reception

Crystal Detectors were found to be more reliable than the coherer but were even more mysterious.

Karl Ferdinand Braun, (and several others), was looking for proofs and discrepancies  in Ohm’s law when he noticed that the law did not apply to crystals. They had variable resistance depending on where on the crystal he applied a point contact.
According to Wiki: The “asymmetric conduction” of crystals was discovered in 1874 by Karl Ferdinand Braun. https://en.wikipedia.org/wiki/Crystal_detector_%28radio%29

Although the invention of the crystal detector is often attributed to Braun, it was left to others to discover that it could be used for wireless and later audio radio signal detection.  Braun was therefore only responsible for “asymmetric conduction of crystals” and not for their use in wireless/radio detection. Braun seems to have been someone uninterested in discovery although greatness was thrust upon him by subsequent historians and a Nobel prize he said should have gone to Marconi alone.
See Wireless/Radio Skulduggery


The first reported uses of a crystal detector was by an Indian professor of Physics at Presidency College in Calcutta named Jagadis Chandra Bose. He demonstrated the use of a diode using galena (lead sulphide) crystals and a metal point contact. He filed a U.S patent for a point-contact semiconductor rectifier for detecting radio signals in 1901...
… Ferdinand Braun patented his own detector on 18 February 1906.

Cat’s Whisker

The basic set-up of the day was a crystal of choice placed in a brass cup (connection) and a cat’s whisker (thin wire) on the end of a lockable swivel cantilever, to lightly touch the top side of the crystal. It was eventually found possible to discard the crystal and achieve detection by touching the brass cup alone; of such are the mysteries of early signal detection. Again we have a loosely contacting device that does strange things.

The coherer is not a rectifier The crystal detector is a rectifier but they both detect radio waves. They both do the same things because they are basically the same: small points in contact.

Wiki: The temperamental, unreliable action of the crystal detector was a barrier to its acceptance as a standard component in commercial radio equipment and was one reason for its rapid replacement by vacuum tubes after 1920. Frederick Seitz, a later semiconductor researcher, wrote: “Such variability, bordering on what seemed the mystical, plagued the early history of crystal detectors and caused many of the vacuum tube experts of a later generation to regard the art of crystal rectification as being close to disreputable.”

Disreputable is a strange word to use regarding a technology that was in its early stages of development. But its all part of the mainstream disdain for technology. The reader will recall Wolfgang Pauli (above) “one shouldn’t work on semiconductors, that is a filthy mess; who knows whether any semiconductors exist”.

It seems it was the work of Bell lab’s engineer Russell Ohl in the 1940’s that led to the refinement of crystals that would enable the mass manufacture of stable diodes for wartime radar equipment – a process that was later to be crucial in the development and manufacture of Bell lab’s transistors. See also: https://en.wikipedia.org/wiki/Russell_Ohl

Electrical Engineering Stack Exchange
– what does the (crystal) rectifier do in a crystal radio?

The following website is a forum and the reader can judge from the answers given that the problem of how a crystal detector works is not going away any time soon:
electronics.stackexchange.com: “Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts.
Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top”

After reading the Stack Exchange answers I recalled, many years ago, actually doing the experiment myself. I found it is possible to receive audible radio signals with a pair of dynamic headphones, a crystal detector, an antenna and an earth connection – nothing more – no other components, no filters. And so I would suggest that most of the answers given at Stack Exchange are wrong and made wrong by incorrect information being taught at student level. We find that David Hughes also heard an audible signal with nothing but a carbon mic and a dynamic earphone… no filters. These people don’t read any history!

Wartime Foxhole Radio Thanks to pinterest.com The razor blade was blue – coated or annealed

Envelope Detector (Crystal Detector)

Wiki: An envelope detector is an electronic circuit that takes a high-frequency signal as input and provides an output which is the envelope of the original signal. The capacitor in the circuit stores up charge on the rising edge, and releases it slowly through the resistor when the signal falls. The diode in series rectifies the incoming signal, allowing current flow only when the positive input terminal is at a higher potential than the negative input terminal. https://en.wikipedia.org/wiki/Envelope_detector

Again, I’m not sure where Wiki editors get their ideas but a crystal detector will work without the capacitor or the resistor. Wrong Wiki!

Wiki tries to explain: An envelope detector can be used to demodulate a previously modulated signal by removing all high frequency components of the signal. https://en.wikipedia.org/wiki/Envelope_detector#Demodulation_of_signals

Envelope Follower

Wiki tells us that the envelope (in red) is what the crystal detector detects. But it does not exist in any realistic sense – it’s just a drawn red line that ‘represents the modulation of a high frequency signal’ – it’s not the actual signal but a representation of where the signal would be if there were one. If the high frequency signal is removed, as we are told above, there’s nothing left, nowhere to draw a red line. The figure above shows an oscilloscope trace of a modulated signal, it shows peaks and troughs representative of changing voltage. It fails to show what is actually going on in the crystal. A description or a rationalisation is not an explanation

Further, what happens when a coherer is used? If there is no rectification as with the crystal detector the red line would be both top and bottom cancelling itself out?  The crystal detector and the coherer are doing the same job but not working in the same way. So how does this work?
The only logical answer to this question is that the high frequency is changed into one that is audible, something that can be heard with a human ear. So is the coherer, the semiconductor diode or transistor and the vacuum tube each a frequency changer, converting radio frequency into audio frequency? The idea has never been explored.

It would be well to remind the reader at this point that originally it was a spark gap that created the modulated signal. Is it not logical to suppose that the crystal detector and the devices that succeeded it are somehow doing the same thing? That micro-sparking is taking place at audio frequencies in coherers diodes and transistors?

Wiki: “…the vacuum tube experts of a later generation to regard the art of crystal rectification as being close to disreputable”
They didn’t know how their own vacuum tubes worked, something that persists to this day. See page: Electron
There are serious theoretical and logical problems…

No one has ever been able to explain how or why the crystal detector works.

Vacuum Tubes (valves UK)

See page Electron 1

Transistors are a development of  crystal detectors

If we don’t know how the crystal detector works, then how are we to explain how the transistor works, as it was a development of the crystal detector?

computerhistory.org: The work of Ohl and Scaff led to a giant leap forward in semiconductor material technology as silicon and germanium diodes were deployed for the war effort. Researchers in Great Britain and the United States developed techniques to purify both elements and “dope” them with selected impurities to obtain the desired characteristics. Countless microwave frequency diodes were fabricated for use in Allied radar receivers. Semiconductor material quality improvements flowing from this work enabled the fabrication of the first transistor at Bell Labs in 1947. http://www.computerhistory.org/atchm/who-invented-the-diode/

Shockley’s book explaining how the transistor works?

Shockley thought he knew how the transistor worked and wrote a book on the subject.

Wiki: (Bardeen and Brattain’s) final design of a point-contact transistor had two gold contacts lightly touching a germanium crystal that was on a metal plate connected to a voltage source. Also known as the “little plastic triangle,” it became the first working solid-state amplifier.

(They) demonstrated the transistor device to Bell Lab officials Dec. 23, 1947. Shockley was reported to have called it “a magnificent Christmas present.” But Shockley himself was not present when it happened and was said to be bitter over losing out on that day. He had his revenge, though. Shockley continued to work on the idea and refine it. In early 1948, he came up with the bipolar or junction transistor, a superior device that took over from the point-contact type.
Bell Labs publicly announced the first transistor at a press conference in New York on June 30, 1948. https://www.wired.com/2009/12/1223shockley-bardeen-brattain-transistor/

John Bardeen, Walter Brattain’s first transistor

transistor 1

Using improved semiconductor materials developed (by Russel Ohl et al) for radar detectors during the war, in early 1945 Shockley experimented with a field-effect amplifier, similar in concept to those patented by Heil and Lilienfeld, but it failed to work as he intended.

In 1981 the semiconductor physicist H. E. Stockman said “Lilienfeld (who had a transistor in  1926) demonstrated his remarkable tubeless radio receiver on many occasions, but God help a fellow who at that time threatened the reign of the tube.” See Bell Labs Memorial: ‘Who really invented the transistor?’, starting at “Oscillating Crystals”:

Bell Labs Memorial: Who really invented the Transistor? is here:

AIP American Institute of Physics
Oral History Interviews
Interviews that offer unique insights into the lives, works, and personalities of modern scientists

DO you believe that Shockley’s decision in 1945 or 46 to focus on silicon and germanium derived directly from his earlier conversations with you in Holmdel?

I think it had a great deal to do with it. The discovery of the NP junction was a new discovery and they hadn’t known about that. That, as I pointed out, was the breakthrough in solid state physics that they were looking for and hadn’t found. Nobody had found that and that was really a great breakthrough. That was a landmark in solid state physics. And of course they say that was accidental, but the discovery of the transistor effect was just as accidental. Brattain wasn’t looking for it. Very often all great discoveries come that way. They are not a matter of great genius, but they happen because the person who finds them is trained in that sort of work and he recognizes it. They are made that way.

Ohl, Bardeen, Brattain and Shockley had Lilienfeld’s 1930’s transistor patent to work from, “but they happen because the person who finds them is trained in that sort of work and he recognizes it. They are made that way.”

The Lilienfeld transistor patent 1930

Note the + connection to what seems to be a crack in the crystal. The same thing is noted by Bell Labs engineer Russell Ohl but he fails to mention Lilienfeld. The crack is the PN positive negative junction?

pbs.org: The crystal had a crack down the middle. Ohl was examining how much current flowed through one side of the crack versus the other, when he noticed something peculiar. The amount of current changed when the crystal was held over a bowl of water. And a hot soldering iron. And an incandescent lamp on the desk in the room.

By early afternoon, Ohl realized that it was in fact light shining on the crystal that caused this small current to begin trickling through it. On March 6, he showed his prize silicon rod to Mervin Kelly. Kelly quickly called Walter Brattain and Joseph Becker to the scene.

Ohl had his coal-black crystal attached to a voltmeter in front of him. He turned on a flashlight, aimed it at the silicon, and the voltage instantly jumped up to half a volt. This was ten times anything Brattain had ever seen before. He was stunned, but not too stunned to produce an off-the-cuff explanation. The electrical current must be due to some barrier being formed right at the crack in the crystal.

Lilienfeld left clear instructions to Bell lab’s on transistor design and construction, it had nothing to do with quantum physics.

Lilienfeld Transistor Radio Circuit 1930, again with a + connection to a crack in the crystal. You would think after all these years someone would notice and ask what’s going-on?


Above is another loose contact device, the Robert Adams Crystal Amplifier of 1933, a point contact transistor based upon the cat-whisker principle all-but identical to the the Bell lab’s original point contact device. Adams said he did not patent the device because the idea was widely known at the time. Adams was the founder of the New Zealand section of the Institute of Electrical and Electronic Engineers IEEE. In spite of this Wiki has removed his page and linked his name to the Wiki page ‘Perpetual motion’ due to his high efficiency Adams Motor that has been built and witnessed working by scores of people. This includes the author who is opposed to perpetual motion which is impossible…. See page on ‘Free energy: Wiki lies’

                                                          Bell lab’s point contact transistor above

It’s interesting that a transistor works in much the same way as a coherer. The small radio frequency current reduces resistance to the larger current


Nikola Tesla recorded visible halos and physical sensations of radiation on his skin from the coil marked ‘Secondary Winding’. The coil was energised with only one connection as shown above. Another loosely coupled spark-gap device that illustrates missing knowledge in mainstream theory.

Yet another loose contact electrical device:
Dr. Deborah Chung’s Negative Resistor



Dr. Deborah D. L. Chung
Dr. Deborah Chung

Dr. Deborah D. L. Chung, professor of mechanical and aerospace engineering at University at Buffalo (UB), is the leading “smart materials” scientist in this country, and a scientist of international reputation. She holds the Niagara Mohawk Chair in Materials Research at UB and is internationally recognized for her work in smart materials and carbon composites. On July 9, 1998 in a keynote address at the Fifth International Conference on Composites Engineering in Las Vegas, she reported having observed apparent negative resistance in interfaces between layers of carbon fibers in a composite material. The negative resistance was observed in a direction perpendicular to the fibre layers. (See Carbon Whiskers below)

Her team tested the negative resistance effect thoroughly, for a year in the laboratory. There is no question at all about it being a true negative resistor. Dr. Chung submitted a paper describing the research to a peer-reviewed journal, and the University filed a patent application. Several negative articles appeared quickly in the popular scientific press. Conventional scientists were quickly quoted as proclaiming that negative resistance was against the laws of physics and thermodynamics. Others thought perhaps the UB researchers had made a little battery and were unaware of it.

On the web site for the University of Buffalo, it was announced that the invention would be offered for commercial licensing. A Technical Data Package was available for major companies interested in licensing and signing the proper non-disclosure agreements. Shortly thereafter this was no longer true, the data package was no longer available, and there was an indefinite hold on licensing and commercialization. It is still on hold as of this writing.

See another page on Chung
I’m told that a free energy device can be constructed from two flat plates separated by a thin film insulator.


Carbon, Metal and Crystal Whisker Growth

Carbon Whisker Growth

A plausible clue to how the things above work is through the growth of ‘whiskers’. Such growth occurs in graphite, metals and crystals, the whiskers may and more than likely do have semiconductor and other properties. I find it interesting/surprising that researchers have taken little account of whisker growth in an electric field and whether growth can be enabled or enhanced by such a field?

Wiki: A monocrystalline whisker is a filament of material that is structured as a single, defect-free crystal. Some typical whisker materials are graphite, alumina, iron, silicon carbide and silicon. Single-crystal whiskers of these (and some other) materials are known for having very high tensile strength (on the order of 10–20 GPa). Whiskers are used in some composites, but large-scale fabrication of defect-free whiskers is very difficult.

Prior to the discovery of carbon nanotubes, single-crystal whiskers had the highest tensile strength of any materials known, and were featured regularly in science fiction as materials for fabrication of space elevators, arcologies, and other large structures. Despite showing great promise for a range of applications, their usage has been hindered by concerns over their effects on health when inhaled.

Whisker (metallurgy)

Whisker carbon in perspective

Click to access PNAS_2014_E-whiskers.pdf

Carbon amplifier

Silicon carbide whisker

Loose contact technology is full of surprises and questions that are begging for answers. Modern theory fails to adequately explain any of the above and so it can only be assumed that academics conjure theories out of the air. The strange thing is, having almost completed this page I came across the link below, by a budding academic and it confirmed everything I had written! It’s a bit long-winded but it’s all there and more if anyone wants to read it…
Coherers a_review_TOC_Fixed

Some More Links

See page Electrical Fortean Phenomena

See also page Undeserved Nobel Prizes Transistor

The Free Energy Secrets of
Cold Electricity
Peter A. Lindemann, D.Sc.

Spontaneous Growth of Metal Whiskers on Surfaces of Solids: A

For those who think they need to be a physicist to construct a transistor:-

Click-Transistor fabrication: so simple a child can do it

Click- Homebrew NMOS Transistor Step by Step – So Easy Even Jeri Can Do It

Click- Make a Point Contact Transistor at home


                                                                        The Digging Dog

Comment from removed page:

One thought on “Microphone-Coherer: Extraordinary”

  1. Part of the problem is our tendency to isolate things, objects, when in reality everything is connected, presumably, at the quantum level.

    The simple experiment of plastic tube, metal filings, fan and battery with pizeo-lighter – the spark seems to complete the circuit between the two electrodes or screws so that the metal filings adhere to each other and to the electrodes thus completing the circuit. He has to physically knock the metal fillings so they fall and disconnect the circuit.

    So how does a transient spark cause the filings to cohere and connect to the electrodes?

    My brain has turned to pudding.

5 thoughts on “Loose Contact Devices

  1. Unlike Thomson, Ernest Rutherford and Niels Bohr were not much into aether science, and propagated much particle physics. Seems their progress are in the time where natural philosophy was lost.


  2. Hi
    What you’re seeing is the abandonment of logic. I wrote to the guy at the link below about this some years ago (He’s not with us any more). We exchanged several Emails. At the time he had admitted that science does not use logic: https://www.lockhaven.edu/~dsimanek
    It all started with him debunking a page I did about John Keely
    I gave him some logic. At the end of the conversations I asked him if I could publish his replys to my questions and he said no. The point being don’t be intimidated by these charlatans.

    I wanted to ask: Browsing the web I came upon an experiment similar to the ones (Thomson?) on your page. It was a cathode ray tube bent at a right angle with a coil each side of the bend. It said the output anode end of the tube had no magnetic field. I don’t know why but I failed to get the link. Have you seen it and if so send a link.


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