From: SFPhysics@aol.com
Date: Sat, 21 Feb 1998 16:53:06 EST
To: pinhole@exploratorium.edu
Subject: Re: Sea Foam and Xtal Sets....
> As I watched the sunset, I was hit in the face by a large clump of foam.
> Does anyone know what causes this foam to form?
> Eric Muller
> Foam usually requires some detergent residue in the water. I would guess
that
> our offshore ocean water has some in it. The wind or churning does the rest.
Neil Fetter
> From: Tim Ostrom <576587@ousd.k12.ca.us>
> Subject: Crystal Radio antennas
> I have been working on a lesson where my 7th graders make crystal
> radios. One radio works great < : When I hook 2 radios to the same
> Antenna and I change the Capacitance (station) on one radio, the other
> radio becomes out of tune without its Variable Capacitor being touched.
> The only solution I can think of is to put 15 antenna wires out of my
> classroom window. Is there a better way? If the 15 wires are too close
> together will they interfere with each other? How long should the wires
> be? I have read to use horizonal long wires. Will vertical wires work?
> Tim Ostrom
> Oakland Unified School District
Hi Everyone -
The "sea foam" is a legacy of the detergent left from incomplete treatment of
the waste water run-off. Even highly treated effluent still contains some
detergent. The petroleum based detergents are some of the most difficult
substances to remove from the gray water. San Francisco has no storm drains,
only sanitary drains that collect ALL water in the City. Large amounts of
run-off from storms are allowed to go into the ocean after only solid waste
has been screened out. The cross-town sewage tunnel around the bay waterfront
was put in place to reduce the untreated sewage reaching the bay and shunt it
to holding tanks for later treatment. This year must surely have taxed the
system to the maximum. BTW - the new holding tanks in back of the SF Zoo are
being paid for by a bond with taxes taken off the water bills of everyone in
the City.
CRYSTAL RADIOS!
1) To answer an earlier question, the reactance of the coil in Henrys is a
function of the square area of the coil. You can use the round coil formula
on a square coil form as long as the area of the square coil is the same as
that of the round coil.
2) You cannot put two tank circuits (crystal radios) on the same antenna
without them changing the Q factor,etc. Each output for my crystal sets is a
separately driven transistor amplifier from the common antenna. Thus the
individual bandwidth of the crystal sets, the tuning range, and the
sensitivity remains unaltered.
3) Antennas do have some effect on each other when closely located. Your
best solution might be to have just one student at a time use the antenna.
Vertical antennas do not help low-frequency AM stations to any degree. The
wave is mostly a ground wave with polarization in a horizontal plane parallel
to the earth's surface.
4) The longer the wires the better for AM reception. Also, don't forget
about having some external lightning protection and make sure the radios have
a solid ground connection for best reception.
I know this quickly dashed posting is missing information I should have
included and is probably clear as mud but this is what you get for free . . .
. ;-)
Al Sefl
SFPhysics@aol.com
"The most incomprehensable thing about the universe is that it is all
comprehendable." - - Albert Einstein before he tackled quantum
physics....