Metal - old style Diodes

Sure it is still possible. Google copper oxide rectifier and selenium rectifier. You can still buy either, occasionally on eBay, also. And if you heat a piece of polished high carbon steel till it turns blue and touch that surface with a nickel or chrome plated pin point I think you get a detector diode.

The minerals galena and zincite were used as crystal radio detectors, essentially point-contact diodes, in the 1920's. The "foxhole radio" used a rusty razor blade. By the mid 1940's, microwave mixer diodes were being made from germanium, silicon, and GaAs.

There were early electrolytic rectifiers, too.

I sort of doubt the fillings/house stuff.

John

folklore has

Maybe not but you can get rectification in odd situations. I ran a twisted pair about 150 ft to extend a phone line to an outbuilding and started hearing a radio station on the remote phone.

You were not getting rectification.!.. I'm sure if you really think about it, you'll figure it out.!~...

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How could he hear a radio station without rectification going on?

Cheap electronic phones (RatShack mainly) pick up AM and TV stations pretty badly, but because the semiconductors inside are rectifying the RF.

Lots of opamps will rectify RF and create nasty offsets.

John

Also see coherer

Rubbish.

One of the rectifier construts was made via copper and copper oxide; not too efficent and (i think) low reverse voltage standoff.

Concerning something vibrating to local stations, it is *not* rubbish; a metal fire-escape ladder can do so thus:

1) the iron structure is long enough to act as an antenna, especially "local" to the transmitter 2) the rust on it creates the detector (iron/iron oxide) 3) that detector is "shorted" by the structure, allowing a reasonable current to flow (in the order of 10-100 mA) 4) that current causes the fire-escape ladder to vibrate. That had been confirmed, at least in downtown San Francisco after (a) someone finally *listened* to a number of drunks and so-called crazy people, (b) the station determined that their coverage in a certain direction was greatly impared, (c) the station techs determined that the fire-escape ladder was in line of the reduced coverage, and (d) anyone near the ladder heard exactly what the station was transmitting: news, music, etc. Cleaning the ladder of the rust solved the problems.

You don't find those on too many homes.

That's crazy. If the station's coverage was "greatly impared", the fire escape would have to be dissipating kilowatts. If one rusty fire escape can affect the far-field radiation pattern of a radio station, what would a tree do? A kid with a longwire antenna and a crystal set? An electrical substation? The Bay Bridge? My company is in downtown SF, and I wish I could steal a couple of free kilowatts.

And what's the sound transducer mechanism? The only radio transmitters in SF are on Sutro Tower, and it's way up on the top of Twin Peaks, a couple of miles + a couple thousand vertical feet from downtown.

Urban legand, and not a very good one.

John

prisoners of war used blued razor blades or coal as detectors in crystal sets, conventional crystals are galena (mineral lead sulphide) which is metallic in apearance. these days semiconductors are used.

it'd happen, but it's unlikely to be a measurable effect.

Bye. Jasen

Yes, copper oxide, selenium and galena (Lead Sulfide) were common before WW2. Galena was found in some types of coal, and that was used in conjunction with a "cat's whisker" usually of tungsten wire, as a point contact diode. I remember trying that with a "crystal set" back in the 50's but got better results with a rusty razor blade. AKA the foxhole radio, and also used in POW camps.

Have heard of it, but suspect it's urban myth stuff.

Barry Lennox

On a sunny day (Sat, 16 Dec 2006 18:54:10 -0800) it happened John Larkin wrote in :

the

Hum, nobody has mentioned that BIG metal rectifier workhorse:

Mercury is a metal after all :-)

SNIP "> Also, some claim that a house can vibrate to local radio stations due to the

Not rubbish at all, sort of. My wife can clearly hear the cable TV channel when the TV is switched off. I can hear absolutely nothing and I'm talking

3am in the morning and you could hear a spider walk across the ceiling. Any theories?

[ snip ]

One not-so-silly effect coming from rusty metal near high-power transmitters is "rust noise", which is wideband RF noise created from non-linear RF current conduction of the rusty joints. This nonlinearity is the same effect exploited in crystal detectors, namely a quantum-mechanical tunneling junction. For this to work one needs two conductors in close proximity, about 0.1 to 0.3nm, but not touching. The conductance is nonlinear, and rectifying. An example of a debilitating rust-noise effect is degradation of RF receivers on a ship when one of the transmitters is operating.

--
 Thanks,
    - Win

No, I'm not quite that old, but there were many rectifiers in use before silicon or germanium--

• Old crystal radios used crystals of various elements, often lead (galena), or various carbides.

• For power rectification, early amateurs used some sort of electrolytic cells, dissimilar metals in a conducting solution will have a directional preference. These were not terribly efficient, as there are many trales of boiling rectifiers, but they certainly were cheap and effective and didnt require a billion dollar silicon foundry.

• Later on copper oxide came into use-- early auto and airplane alternators had copper oxide rectifiers. Also many older AC voltmeters have copper-oxide bridges.

• Don't forget mercury-vapor rectifiers! Old battery chargers from the 1930's often had a Sylvania "Trygon" tube, basically a 10 amp mercury vapor rectifier.

• Also most any kind of oxide can act as a rectifier. Many years ago I lived about a mile away from a 50KW AM station. One night while sneaking back home at 2AM I heard talking in the garage! Busted! I thought. I wandered ahead, head down toward the talking, expecting to get a talking-to from my parents. Turned out the voice was coming from a rusty electrical box! It was the overnight talk-radio show from the radio station, coming in loud and clear. A rusty hinge was rectifying, and enough current was flowing through the metal cover to act as a speaker cone. It went away as soon as I touched the cover. Weird.

the

Beautiful.

There was also the ignitron tube, a pool of mercury with an igniter electrode and a big graphite anode, usually water cooled. They were used as very high power rectifiers and triggered switches. They were usually ugly. In pulsed applications, they could handle up to a million amps.

John

No doubt. Even the plating in new 7/16 connectors has to be right or the nonlinearities can mess up cell phone sites. But the field strength in downtown San Francisco is nowhere near what you'd see on a ship, right under the antennas. We're in a pretty much rf-transparent building, and we can see Sutro Tower out the back window, and the most we see is a little fuzz on the faster scopes. And we *do* have a rusty fire escape!

"their coverage in a certain direction was greatly impared" is still unbelievable. No small-scale passive structure is going to poke a significant directional hole in a far-field radio pattern. As I said, a tree would have a bigger effect than a fire escape ladder, and no radio station owners are going out chopping down trees.

John

fillings in her teeth ?

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Is her name Claire Voyant ?:-)

...Jim Thompson

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