Re: coherers

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<evp-at-pacbell-dot-net>

>         On the subject of "old wireless" stuff, here's a question for
Antonio:
> 
> Have you ever built a "magnetic detector"?  I've read of them a lot, but
> have never seen a single statement about their sensitivity.  They were
> reported as "less sensitive than a coherer" [if that is possible] but
> much more stable, and were standard Marconi equipment for several
> years.  I've always wanted to make one but can't find the fine,
> insulated iron wire.

I have not tried to make one, but there is one at a museum in my
university. It has a loop of iron wire (I am not sure if the wire
is still there) moved between two pulleys by a clockwork mechanism.
The wire passes close to a pair of magnets and inside a coil with
two windings. One of the windings goes to the antenna and the
ground, and the other to a phone (that is there too). The iron wire
doesn' have to be insulated. The idea is that the wire gets magnetized
by the magnets, and is demagnetized by the RF signal (probably as 
in a "degaussing" system, used in TVs, monitors, etc). When this 
happens a click is heard at the phone.

Antonio Carlos M. de Queiroz