Re: [Fwd: Magnetic Field in a Flat Spiral]

["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>

> > David Sharpe wrote:
> >
> > > Ed
> > > Not doubting may have to go to NIB or SaCo to get
> > > BH product high enough to do the job.  However if
> > > I mount in a 'C' magnetic armature (1), and shape pole
> > > faces to focus what magnetic flux we got (2), we may be
> > > surprised at the available flux density.  The magnetron
> > > ring magnets are cheap, compared to a rare earth, and
> > > magnetic quenching was captured on a video tape at
> > > Richards nearly 8 years ago, using a WWII Alnico
> > > magnetic radar magnet.  These modern ferrite magnets
> > > are at least 3X to 5X stronger then first (and second)
> > > generation alnico products.  Worth giving it a whack
> > > and see what falls out of it.

	Not having access to that tape, and being too cheap to buy it, wonder
if you could just give a word summary of what happened? Not sure what
WWII magnetron magnet you used.  Typical flux density for the S-Band
maggies was about 1000-1500 gauss across a gap of the order of 1-1/4",
and for X-Band it was about 2500 gauss across a gap of the order of
5/8".  I don't have my magnetic properties handbook here at home, but
think you're mistaken about the relative magnetizing power of the
ferrite and alnico magnets.  If I can remember I'll take a look at that
next week.  By the way, one of the permanent magnetic materials
companies has some excellent reference data on magnets on its web page,
but that is also bookmarked at work and not at home.  They most
specifically compare the ferrites and more modern rare-earth magnets
with the various alnico's and nickel-iron.

> How about electromagnets? The time delay between initial current pulse
> and magnetic activity would give an interesting twist to "tuning"?
>  I think the diac\Triac pair would work, but then a real circuit?
> I like it!
> 
> Marc M.

	Electromagnets were used for quenching during the entire era of ARC
transmitters.  They were hooked in series with the arc and thus provided
the stabilizing effect of series inductors.  The current in the magnet
varied as the arc current varied, which may have provided some sort of
current regulation, though don't remember seeing any discussion about
that.  No doubt that electromagnets would work in Dave's application and
have the advantage of adjustability, but it would take a lot of a magnet
to equal what those little permanent magnets can do!

Ed