Coil Construction, was: [AMRadio] Fun with 4D32's...


Larry Keith kq4by at rocketmail.com
Thu Jan 4 11:46:48 EST 2007


You can buy approximately 1/8" thick Lexan (or
polycarbonate) in 8x10 sheets at Lowes or Home Depot..
 I cut it into 3/8" wide strips, using a small bandsaw
and a fence.  Other dimension Lexan sheets can be
bought at U.S. Plastics or McMaster-Carr.

I have a stack of already-cut ribs (10" long x 3/8
wide" that would have to be drilled. If you just want
a few to play with, verify that your QRZ address is
good and I will send you some (8 or so?)..

And, I have some factory-punched strips that are good
for AWG 12 wire, 6 TPI..  I had to pay for those and
order a 1000 to get them. 8-)  If you want to try
those, I need to get $10 for 4 strips (10" long x 3/8
wide x .090 thick). No charge for shipping.

I have forgotten what size wire you were planning to
use.  I have found that my "process" becomes more
difficult if I use less than # 12..  I have had good
results using AWG 8, 10 and 12.  And, you can get that
wire at The Wireman..  Buss wire, solid copper tinned.

BTW, with 1/8 or so thick stock, a 3/32 drill works
good for #12, 7/64 will work for #10. I have lost my
notes for # 8 but I would start with a drill size that
is slightly larger than the wire diameter. Too large
will work but too small will bind! 

 You can stack the ribs together and tape them (I use
wide masking tape, just about two layers, at each
end).  Then you drill all the ribs at once..

As you thread the wire through the ribs, wear some
cotton gloves.  Try to keep the ribs straight and
evenly-spaced as you do the threading.  I have found
that if the wire starts to bind a small squirt of
WD-40 along the rib will help.

After the coil is threaded, position the ribs and run
a bead of model airplane cement along the rib where
the wire comes through.  Do a rib, let it dry, then do
another rib, etc.. until all four are done.  I usually
do both sides of the ribs to get a "firm" coil.

Let's see: form size is usually 3/8 to 1/2 smaller
than the desired coil diameter.  I use a 2 5/8 coil
form made from PVC pipe couplings to produce 3"
diameter coils.  It is pretty close.

And, I wind the coil with moderate tension by passing
the wire through a bench vise (padded with a shop
towel).

Figure out the number of turns and add about 10
per-cent to allow for expansion.  So, when I wind a 60
turn coil, I actually wind about 66 turns on the coil
form.  If you need long coil leads, add a couple of
turns..  You can always cut off the excess -- it's
tough to add wire to the coil..  8-)

Hope that helps..

73,

Larry
KQ4BY


--- Brett gazdzinski
<brett.gazdzinski at verizonbusiness.com> wrote:

> Larry,
> Where do you get the strips of plastic to drill
> and pass the coil through?
> 
> Brett
> N2DTS 
> 
> > -----Original Message-----
> > From: amradio-bounces at mailman.qth.net 
> > [mailto:amradio-bounces at mailman.qth.net] On Behalf
> Of Larry Keith
> > Sent: Tuesday, January 02, 2007 1:19 PM
> > To: 'Discussion of AM Radio in the Amateur
> Service'
> > Subject: RE: Coil Construction, was: [AMRadio] Fun
> with 4D32's...
> > 
> > 
> > 
> > 
> > 
> > Thanks Larry.
> > How do you keep the spacing of the holes
> > exact?
> > 
> > I have a "homebrew" table that attaches to my
> small drill 
> > press.  The table
> > has a fence and a stop.  I use spacers (plywood 
> > strips)stacked against the
> > stop.  I drill a hole and remove a spacer,
> reposition the 
> > work, drill a
> > hole, etc..
> > 
> > 
> > Since the handbook says the antenna tuner is good
> > for 250 watts of AM, I would need to at least
> double
> > the size of things, from the #14 at 8 tpi, about
> > a foot or more long, to ?
> > #10, or #8, or thin copper tubing?
> > 
> > I have built coils using #12, #10, #8 and using
> copper 
> > tubing, using the
> > same construction methods.
> > 
> > 
> > 
> > 
> > Balance is important, maybe hard to do with
> > a home brew coil..
> > 
> > Why?
> > 
> > 
> > 
> > I did not study the text, not sure if its supposed
> to
> > cover 160 meters, but if I built one, might
> > as well include 160...
> > 
> > You just doubled the coil size, if it wasn't
> designed for 160...
> > 
> > 
> > 
> > I know I will need to make some sort of coil 
> > form/support to achieve a good balance.
> > 
> > Polycarbonate sheet.. Mounted on stand-off
> insulators..
> > 
> > 
> > 73,
> > 
> > Larry
> > KQ4BY
> > 
> > 
> > 
> > 
> >
>
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Larry Keith 
231 Shenandoah Trail 
Warner Robins, GA 31088-6289 
  kq4by at rocketmail.com
larry.keith at yahoo.com 
478-329-0030




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