Hand winding coils for L-match

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Is there some magical trick to hand winding coils for a match box?  I am building a tuner for a random wire and attempting, without success, to wind the inductor. 

I am using a 2" PVC core and 14g bare copper.  So far I have mastered the copper slinky. 


 ??? ??? ??? ;D

Dale Hunt:
Chucking the former in a drill or rotisserie so it rotates as you guide the wire
onto it does make things a bit easier.  For some 160m loading coils I slipped
the former over a board stuck in a vise and put a screwdriver through a pair
of holes in the far end so I could turn the former with one hand while feeding
the wire with the other.  (But that was using a much thinner wire.)

There is a method described in the Technical Topics column of the RSGB
journal RadCom that sounds good, though I haven't tried it.  Put a bolt
and nut on each end of the PVC former.  Secure one end of the wire under
one nut with several inches to spare, wind on the wire, and secure the other
end in a similar manner.  If the wire isn't snug, start at one end and twist it
on tighter with your hands, pulling up the slack at the far end and resecuring
the wire end.

Then put the whole assembly in the freezer for a few hours.

The PVC shrinks more than the copper,  so the wire will be more loose.
Repeat the process of tightening the windings, pulling more slack out of
one end.  Repeat a couple times, and, when warm, the copper wire will
actually be indented slightly into the PVC former, making a reasonably
permanent coil.

On the other hand, if you want a self-supporting coil without the former,
then the secret is to wax or oil your coil form (or coat it with wax paper),
wind on the wire, and run 4 strips of epoxy the length of the coil to act as
spacers.  Once the epoxy is dry you can remove the coil former (that's why
the wax or grease - so the epoxy doesn't stick to it) and the coil should
hold its shape.

Other methods:  drill holes in a flat sheet of plastic for the turns of the coil
(making sure that those on one side are offset half a turn from the other side)
and take one of your slinkies and thread it through the holes as if you are
screwing it into something.  That gives you a flat mounting plate with minimum
plastic in the field of the coil.

One other approach if you want to be able to tap the coil in various places:
mount 9 dowels or nails evenly spaced around a circle (other odd numbers
may work as well).  The easiest way might be to mark the circle, drill holes
at each point, and slip a box nail through from the back.  The posts have to
protrude higher than the length of the coil.  Then, starting at one point, wind
the wire around every every OTHER post and inside the others.  This makes
a lumpy coil with reduced self-capacitance.  When you get enough turns, you
can run a bead of epoxy along the points where all the wires cross each other.
When it dries, remove the posts.  This gives you convenient "lumps" to tap to.

Peter Chadwick:
Wouldn't go for PVC myself - a bit lossy.

The plastic sheet with holes is probably the easiest unless you have a lathe.

Quote from: G3RZP on March 21, 2013, 10:19:17 AM

Wouldn't go for PVC myself - a bit lossy.

Wasn't able to do an actual differential measurement yet, but I've been seeing Q peaks of 600-700 with PVC form coils here:


Someday I hope to do the same coil with and without PVC.

Claude Stewart:
BYU's recommendation of a slow-turning electric BBQ spit is good, and use a key ring to keep the turns separated. Another way is to wind the wire side-by-side with weed whacker line (it's almost the same diameter as AWG16 bare wire). A final method is to use plastic grommet material, the kind used for insulating electrical wires that runs through bulkheads and firewalls. I think it's nylon U channel that has a notch in it about every eighth inch or so. Once you've got the coil formed, just run a hot glue gun down the U to finish the job. It is best to let the wire go slightly slack and realign the grommet strips before gluing to keep them straight. Just get them slack enough so they'll slide off the PVC former, and you'll have a nice air core inductor. GL.


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