Re: Metal - old style Diodes

On 17 Dec 2006 07:46:30 -0800, Winfield Hill
<Winfield_member@xxxxxxxxxxx> wrote:

John Larkin wrote...
Robert Baer wrote:
Homer J Simpson wrote:
"Heid the baw - goal!!" wrote ...

Before semiconductors were invented we had Diodes for rectification
which were metallic of some sort. Does anybody remember? I am
interested if it is possible to make a Diode from two dissimilar
metals. Why? Well folklore has it that in some rare occasions
people have heard radio stations via two fillings on top of each
other in their teeth.

http://www.adonald.btinternet.co.uk/Crystal/Crystal.html
Also see coherer

Also, some claim that a house can vibrate to local radio stations
due to the metallic structure. Possible or rubbish?

Rubbish.

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

That's crazy. If the station's coverage was "greatly impared" ...

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.

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

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