How does radio work?

[ben m]

My school was in an academic town where new products and concepts were tested.

Difficult to google this one, but I'm learning they were called "induction loops" and may have been mainly targeted for hearing impaired students.

Oh, it seems they are still commercially available

Thanks for the info, that's very interesting.

 

[Mr. Scott]

Electricity goes in, right wing talk shows come out. You can't explain that!

Bill O'Reilly is on the JREF forum?

Actually, we CAN explain that. Could it be---SATAN????

 

[jj]

Detection of AM signals is relatively easy - all you need is a "non-linear" device in an electrical circuit (if it were any more complicated than this then radio might never have taken off).

The point is not that. That is obvious. The POINT is that an electrical signal corresponding to the demodulated AM applied to either the auditory nerve or the cochlea will not do what you think it will do.

 

[jj]

Few are claiming radio reception by dental work happens by direct electrical stimulation of the nerves in the ear. The best hypothesis is that loose fillings vibrate mechanically, because of the huge power of nearby transmitter towers, and that mechanical vibration is transmitted to the ear through the bones.

Given the inefficiency of bone conduction, we better also see people being able to hear WCBS or whatever by listening to the person's mouth.

 

[jj]

Thanks for the info, that's very interesting.

Induction loops are not just "still used" they are common in churches, for the simple reason they support hearing by older people whose hearing aids have an electronic "telephone" pickup.

 

[daxi]

The point is not that. That is obvious. The POINT is that an electrical signal corresponding to the demodulated AM applied to either the auditory nerve or the cochlea will not do what you think it will do.

A radio wave is a non ionising electro magnetic field that is it is both an elctric & a magnetic field & it does not need power to demodulate it. What is being described is the tooth de modulate it, not amplifying it or tuning it in, it is a single accidental frequency receiver, that happens to work.
I don't know what modern tooth filling are. But I would suspect that any demodulation takes place where two teeth have been filled with a conductor & are side by side. This makes a capacitor, which is two conductors separated by a resistor & the right capacitor will make a demodulator.
I have been building & using both radio transmitters & receivers since the mid 1970's & I have a lot of first hand knowledge of the phenomena that causes something to receive a signal it was not designed to receive. It's called Electro Magnetic Incomparability & my experience is that if a tooth does demodulate a radio signal, then that radio signal will have a very strong field strength.
It is certainly a fact that someone with a metal plate over a damaged area of the skill can demodulate a signal & it is certainly within the laws of science that someone with a conductive filling in their teeth could also do the same, but that is not to say it has ever happened, just that it's not poor science to suggest it has or could.
Edited to help it make sense.

 

[MRC_Hans]

Ah,things are starting to become more clear now.

I came up with the frequency range, because it seems so... impossible that something as complex as music could be carried by something a simple as a single wave, but that is what actually happens. If I think about it I still find it hard to understand how a single speaker cone, or a microphone can capture the simultaneous drums, bass, guitar and singing of a rock song. All these tones happening at the same time.... hm. But of course, this is what is happening, because in the end my ear drums are no more than an oscillating membrane too.

Exactly! Of course, you have two eardrums, so there are two similar, but not identical signals, hence stereo.

In a radio, stereo is encoded by shifting between the two signals, at a pace so swift that you can't hear it. Once you have recovered two signals, you filter out the switching frequency and feed the signals to two separate amplifier and speaker systems.

Hans

 

[davefoc]

A radio wave is a non ionising electro magnetic field that is it is both an elctric & a magnetic field & it does not need power to demodulate it. What is being described is the tooth de modulate it, not amplifying it or tuning it in, it is a single accidental frequency receiver, that happens to work.
I don't know what modern tooth filling are. But I would suspect that any demodulation takes place where two teeth have been filled with a conductor & are side by side. This makes a capacitor, which is two conductors separated by a resistor & the right capacitor will make a demodulator.
I have been building & using both radio transmitters & receivers since the mid 1970's & I have a lot of first hand knowledge of the phenomena that causes something to receive a signal it was not designed to receive. It's called Electro Magnetic Incomparability & my experience is that if a tooth does demodulate a radio signal, then that radio signal will have a very strong field strength.
It is certainly a fact that someone with a metal plate over a damaged area of the skill can demodulate a signal & it is certainly within the laws of science that someone with a conductive filling in their teeth could also do the same, but that is not to say it has ever happened, just that it's not poor science to suggest it has or could.
Edited to help it make sense.

daxi, either you or I have misunderstood jj's point.

I don't think jj claimed that an active amplifier was necessary for a radio receiver. He would be wrong if he made that claim. My dad and I (many and many a year ago now) made a crystal radio that produced enough amplitude to be hear radio stations through earphones and radio receivers existed before amplifiers were developed.

I think jj was discussing the issue of the transducer. His first point was that one was necessary and that it was very unlikely that there is any mechanism in a human to be able to sense sound directly from a baseband electrical signal. That seems probable to me also. I asked the question whether it was possible but I didn't know of mechanism by which it would be possible and jj didn't seem to think there was one.

His second point was that if a human did have some sort of happenstance transducer in his mouth that produced enough sound such that the individual could actually hear a radio station then it would also be possible for another individual to hear the sound if the human that was detecting the radio sound opened their mouth. His argument, as I understand it, is that the audio path from the interior of the mouth to the ear isn't all that good and if the sound was loud enough to be heard by the individual receiving the radio signal then it would be loud enough to be heard by somebody else if the individual receiving the radio signal opened his mouth.

Whether he was right about that or not I don't know, but jj seems knowledgeable in these areas and assuming I understood him I suspect he's right. His claim suggests an alternative method of confirming the existence of this phenomena. A sensitive microphone that picked up sound coming out of an individual's mouth would serve as confirming evidence for the phenomena.

FWIW, I looked around the web for information on naturally occurring junctions and do it your self diodes. I did find sites that talked about how to build your own diodes, even LED's but they all involved specific substances that didn't sound like something that would be used in dental care. I didn't find anything about how a happenstance junction might occur or how effective a happenstance junction might be. You are suggesting that naturally occurring junctions are common. Is it possible that one of these happenstance junctions you've discussed could be verified with an ohmmeter? Are you thinking of something that could easily be constructed at home that would constitute a junction with enough of a rectifying characteristic that an ohmmeter could be used to measure the effect?

 

[Mr. Scott]

Given the inefficiency of bone conduction, we better also see people being able to hear WCBS or whatever by listening to the person's mouth.

I don't think "inefficiency of bone conduction" makes the tooth radio as unlikely as you suggest. When I chew potato chips with my mouth closed, it makes a nearly ear-splitting sound that is barely audible to others. Therefore I find it quite believable that being close to a very strong AM signal could make a signal in teeth or braces strong enought to be demodulated and heard privately, and has been pointed out, no law of physics needs to be violated.

I personally don't believe Lucy's story of hearing Japanese transmissions during WWII, the idea was commonplace at the time, so it could have only happened once, and other reports from lying attention whores after that could have been the source of urban legends.

Also, I don't believe a capacitor is needed in a tooth radio detector. I think only ferrous metal (to turn the em waves to current, then to vibrate mechanically) and diode rectification (to turn the AM radio frequency into audio frequency).

 

[daxi]

The simplest form of radio is a crystal radio & the crystal mentioned need not be a crystal, but a anything that will rectify the signal. That is something that will convert the AC current to DC. And that is exactly what a capacitor will do.
All a capacitor is, at it's simplest, is two conductors with a resistor between, be that air, paper or even the teeth's outer surface. Are teeth non conductive?? It's not something I have ever needed to know.
A capacitor passes current in one direction only, thus if a capacitor did exist in someone's mouth it would be the only component needed for the most simple of a crystal radio. In other words the capacitor WOULD be the radio.
I have just found the following "Teeth Braces And Tongue Studs by Jane Thurnell-Read" sorry I cannot put a link in.

An electric current is generated easily when there are two dissimilar metals in an electrolyte. Such a situation can arise in the mouth. The saliva is the electrolyte – a very good conductor of electricity – and dental amalgams are composed of several dissimilar metals. Measurement of these minute electric currents in patients with at least 2-3 amalgam fillings has shown that the electrical output involved is a thousand times greater than that used by the body in nerve conduction. (Robert Hempleman International Journal of Alternative and Complementary Medicine, November 1997)

The above does not prove anything to do with radio reception, but is does suggest that the theory is a viable one.

 

[MRC_Hans]

The simplest form of radio is a crystal radio & the crystal mentioned need not be a crystal, but a anything that will rectify the signal. That is something that will convert the AC current to DC. And that is exactly what a capacitor will do.

Actually, no. A capacitor can filter AC from DC, but it cannot demodulate a signal.

All a capacitor is, at it's simplest, is two conductors with a resistor between, be that air, paper or are teeth non conductive?? It's not something I have ever needed to know.

In principle, it is two conductors with an insulator between. Of course, the insulator may not be perfect, and thus be expressed as a resistor, but the correct term is insulator (dielectric).

A natural tooth is a fair insulator, a filling and flesh are conductors, so a tooth with a filling can be said to form a capacitor.

A capacitor passes current in one direction only, thus if a capacitor did exist in someone's mouth the only component needed for the most simple of a crystal radio also does.

No, that is wrong. A capacitor passes (AC) current in both directions.

For a detector, you need a component that can act as a rectifier. However, you are correct that many components and substances can function as rectifiers, under the right circumstances.

For a detector to function properly, it must consist of a rectifier, a capacitor, and a resistor. However, the two latter are often parasitical to the circuit.

The above does not prove anything to do with radio reception, but is does suggest that the theory is a viable one.

It does have some merit. I would say that two fillings were needed, in that the connection between them (the metal being covered with sulphides) might act as a rectifier. Metal/metal salt transitions are known candidates as rectifiers. The interesting question is how the rectified signal is turned into perceivable sound, but it might be muscles in the cheek vibrating to the signal current, or the fillings themselves being moved by the current.

A large signal strength is certainly required. Sound from the teeth is transmitted quite effectively to the ears. To verify this take a pen ans scratch it lightly with your fingernail. Scratch to lightly that the sound is barely audible. Now, hold the pen between your teeth and scratch it in the same manner. The sound will be clearly audible.

Hans

 

[Jack by the hedge]

I was reminded just today of the (presumably apocryphal) story of engineers at the BBC's large Droitwich^WP transmitter trying to figure out why it seemed to have developed an unexpected "shadow" in its transmitted signal strength in one particular direction. The story goes that an enterprising local farmer had rigged his greenhouses with lots of simple wire antennae to get free heating.

 

[Olowkow]

I was reminded just today of the (presumably apocryphal) story of engineers at the BBC's large Droitwich^WP transmitter trying to figure out why it seemed to have developed an unexpected "shadow" in its transmitted signal strength in one particular direction. The story goes that an enterprising local farmer had rigged his greenhouses with lots of simple wire antennae to get free heating.

Probably not.

The Lucille Ball/Japanese spies story is on Snopes as "undetermined". It seems to me that I saw a video of her telling this story on Johnny Carson's Tonight show, but I cannot find it on YouTube. My problem with her statement that she heard "de-de-de-de-de", as Morse code would be heard on a communications receiver, ie, beeps signalling "dits and dahs", actually International code, is that you really need more than just detection of a CW (continuous wave) signal when receiving transmitted code.

Some ham radio operators still enjoy using "CW" for communications. In order to hear the "beep-beep" sounds, a BFO (beat frequency oscillator) is needed to convert the continuous wave bursts into an audible tone when being received, since the CW signal is not modulated. The BFO is an oscillator that mixes with the incoming signal, and produces a "beat frequency" speaker output. Without such an oscillator, all one hears is silence, essentially.

So I have always wondered how Lucille could hear "beep-beep's" when the RF (radio frequency) energy was simply detected using her fillings. The RF signal alone is oscillating much to fast to produce any vibrations (sympathetic or otherwise) that she could hear, it would seem to me.

 

[Mr. Scott]

The simplest form of radio is a crystal radio & the crystal mentioned need not be a crystal, but a anything that will rectify the signal. That is something that will convert the AC current to DC. And that is exactly what a capacitor will do.

No, a capacitor will not rectify a signal or detect an AM radio signal. MRC_Hans is right. Only a non-linear device, like a diode, will do that. A capacitor is a linear device. Daxi, if you can find a credible reference online that confirms your claim, post it, will you?

I feel certain that a very strong "morse code" signal of the right type can be picked up by mouth hardware of the right type. By "morse code" I mean pulses of radio frequency signal, whatever code (American, Japanese, etc.) is used. Maybe Lucy picked up the signal on her car radio from a land based secret transmitter and embellished it into tooth fillings for the press. Who knows?