Re: Coherer experiments

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Antonio,

Tesla used Coheres in Colorado Springs.  You design is what I have always
heard of too.  However, I think fine nickle filings are usually used.  They
detect the sharp initial wildly noisy gap firing when the gaps internal
capacitance is suddenly shorted.  I am not sure how they would work with
say a CW coil...

Cheers,

	Terry



At 11:35 PM 3/21/2001 -0300, you wrote:
>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
>