Flat spiral coil winding
 

I would try to use the 2 sheets of Plexiglas you mentioned and try to find
a spacer the same thickness as the wire, and try not to pull the wire to
tight on the form, that might make the Plexiglas bend. Where did you find
the metal detector plans that you're using?

David KG2LI

I would try to use the 2 sheets of Plexiglas you mentioned and try to find
a spacer the same thickness as the wire, and try not to pull the wire to
tight on the form, that might make the Plexiglas bend. Where did you find
the metal detector plans that you're using?

David KG2LI

"G=E9ry Duyck" wrote:
=

I made a good deal today!
I bought 12kg (=3D26.5 pounds) of 0.9mm (=3D 20.5awg) varnished coper w=
ire for
20 euro
(=3D$23 US).
Pretty cheap isn't it!
=

I want to wind some flat coils with it to use with my homebrew PI metal=

detector.
=

I place 2 sheets of plexiglass above each other with a round piece of
plastic
with the thickness of my wire and the inner diameter of my coil.
Then I start winding (40 turns).
=

Even if I wind very carefully twe wire keeps on moving above each other=
,
so I don't have a neat sipral :-( It's very frustrating !
=

Now I just do it with one piece of plexiglass and the round piece of pl=
astic
glued on it,
and just wind and glue it together at once.
That's working, but it takes a while before your coil is finished!
=

Is there any trick for winding sprial coils ?
I saw some pictures on the internet with homebrew spiral coils, but wit=
hout
explanation...
=

Any tips or hints would be welcome.
=

--... ...--
Gery D.

The coil does not have to be perfectly flat to have a flat spiral
characteristic. The really easy to make one is to use an
nonconductive coil form shaped like a daisy with an odd number of
petals. You pass the wire between the petals and every turn passes
through the slots the opposite way from the previous turn. This
actually produces a lower stray capacitance coil than the perfect flat
spiral.

-- =

John Popelish

"G=E9ry Duyck" wrote:
=

I made a good deal today!
I bought 12kg (=3D26.5 pounds) of 0.9mm (=3D 20.5awg) varnished coper w=
ire for
20 euro
(=3D$23 US).
Pretty cheap isn't it!
=

I want to wind some flat coils with it to use with my homebrew PI metal=

detector.
=

I place 2 sheets of plexiglass above each other with a round piece of
plastic
with the thickness of my wire and the inner diameter of my coil.
Then I start winding (40 turns).
=

Even if I wind very carefully twe wire keeps on moving above each other=
,
so I don't have a neat sipral :-( It's very frustrating !
=

Now I just do it with one piece of plexiglass and the round piece of pl=
astic
glued on it,
and just wind and glue it together at once.
That's working, but it takes a while before your coil is finished!
=

Is there any trick for winding sprial coils ?
I saw some pictures on the internet with homebrew spiral coils, but wit=
hout
explanation...
=

Any tips or hints would be welcome.
=

--... ...--
Gery D.

The coil does not have to be perfectly flat to have a flat spiral
characteristic. The really easy to make one is to use an
nonconductive coil form shaped like a daisy with an odd number of
petals. You pass the wire between the petals and every turn passes
through the slots the opposite way from the previous turn. This
actually produces a lower stray capacitance coil than the perfect flat
spiral.

-- =

John Popelish

I like John P's suggestion of a form with radial spokes, like a wagon
wheel or like petals of a flat flower. You can make one from wood,
with a wooden disk in the middle, drilled to accept dowels (round
pieces of wood).

This type of coil was/is popular with crystal-radio and other AM-radio
buffs... it's called a "spider web" coil. Use an odd number of
spokes/petals, so that alternate turns on the wire spiral go onto
opposite sides of any given petal.

I gather that one attraction to this winding style is that it results
in a very low amount of parasitic capacitance, and thus a high Q.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

I like John P's suggestion of a form with radial spokes, like a wagon
wheel or like petals of a flat flower. You can make one from wood,
with a wooden disk in the middle, drilled to accept dowels (round
pieces of wood).

This type of coil was/is popular with crystal-radio and other AM-radio
buffs... it's called a "spider web" coil. Use an odd number of
spokes/petals, so that alternate turns on the wire spiral go onto
opposite sides of any given petal.

I gather that one attraction to this winding style is that it results
in a very low amount of parasitic capacitance, and thus a high Q.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!