Re: Coherer experiments

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mark Fergerson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <mfergerson1-at-home-dot-com>

  Hi Carlos, all:

  The need for a "tube tapper" could easily be met with one of those
neat, tiny "buzzers" scavenged from a "dead" cellphone (basically tiny
DC motors with an eccentric weight crimped to the shaft). It could be
set to run from a button Lithium cell (which will operate the buzzer
for around ten minutes continuously) soldered to the leads and the
assembly epoxied to the coherer tube. There's the possibility of
aliasing as the buzzer might decohere the tube while it's trying to
cohere, but a small potentiometer in the circuit should help avoid
that.

  I don't think the magnetic fields from the motor should interfere
with the operation of the coherer, but you might want to check with no
HV nearby.

  Sounds like fun for those interested in TC "radio" experimentation.

  Mark L. Fergerson

> Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <acmq-at-compuland-dot-com.br>
> 
> Hi:
> 
> Has someone ever experimented with a "coherer", or Branly's tube?
> It's a primitive radio detector, used in the early experiments
> about radio transmission. There are many references about it in the
> web, but I didn't find any modern reproduction.
> 
> I made one by enclosing some iron filings in a 3/16" plastic tube,
> loose between two 3/16" brass rods inserted in the tube. With the
> device vertical (it is to be used in the horizontal), the iron
> occupies a space of 8 mm, between the 9 mm spacing of the rods.
> Much to my surprise, this simple device "detects" a spark from the
> discharge of a Leyden jar 2 meters away, by changing resistance
> from 10 MOhms to 1 KOhm. A light tap makes it recover the high
> resistance.
> 
> A 9V battery and a LED in series with the coherer results in a
> nice spark detector. Long wires increase the sensitivity.
> 
> Would certainly "detect" a working Tesla coil close to it too.
> 
> Antonio Carlos M. de Queiroz