Re: coherers

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

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

Tesla list wrote:
> 
> 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

	Your university seems to have a lot of really neat antiques!  That
sounds like the classic Marconi detector, particularly if it is in a
large flat box with the detector mounted on the top panel.  IF the wire
is still there it would be really interesting if you could borrow it and
attempt to measure its properties, an in particular see what the "click"
really sounded like.  One claimed advantage of the device was that it
could produce quite a lot of signal current and operate several
low-impedance headsets in series, permitting multiple operators to try
to transcribe the same message under "difficult" conditions.

	Does anyone remember Tesla talking about such a device?  I don't, but
it is possible considering the many things he experimented with.

Ed