After a week of bobbin making and winder preparation, and with lots of
help from my wife counting off the turns at the hundreds beeper, my
dual voice coil is wound and terminated.  It consists of two coils,
each 3/4" wide, ID of about 1.1" and OD about 1.4" and they are
separated by 3/4".  The spool says 44 ga., but it measures only 2
mils, insulation included, so it is a bit small.  Each coil has 32,000
turns for a total of 64,000 turns and a total resistance of 90,500
ohms.  By wire table, that works out to about 6.6 miles of 44 ga., but
by physical size, it comes out to about 4 miles.  This also makes me
think that the wire is a bit smaller than 44 ga., or it became smaller
after I stretched it to make the spool turn.  :)   

About 7/8th of the way to the end, I broke the wire and had to solder
a splice to be buried in the coil.  Talk about having big hands and
crude tools!

Next step is to add the support rods that hold it up inside the magnet
structure and seal the whole thing in a protective layer of wax.  Then
I can exhale.

I am looking forward to measuring the sensitivity in volts seconds per
meter, to see how it this design measures up, compared to others that
I have been reading about.  The highest sensitivity unit I have seen
has a sensitivity of over 2400 volt seconds per meter.  See HS-10-1 @
210,000 ohms also with a dual coil.

http://www.geosys.co.jp/GEO/Sensor/hs-10.html

-- 
John Popelish
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