Re: Coherer experiments

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Original poster: "Stefan Richter by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Stefan.Mac.Richter-at-t-online.de>

Hi Antonio,
I made some experiments many years ago. There exist some schematics
anywhere in the web how to use such an unit for
receiving morse signals. The problem is, that after receiving a signal the
coherer ( in Germany called "Fritter") has
low resistance. Therefore there was a unit to shake the coherer for a short
moment ("Klopfer"). After that the coherer
has high resistance again and is ready to receive new signal. I am sure you
will find detailled information when using
good search engines.
I hope I could help you a little bit.
Kind regards
Stefan Richter, Germany

Tesla list schrieb:

> 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