Message-ID: <2000041221190568199@zetnet.co.uk>
Date: Wed, 12 Apr 2000 21:19:05 +0100
To: rsgb_lf_group@blacksheep.org
From: "Peter Dodd" <g3ldo@zetnet.co.uk>
Subject: Re: LF: Coil winding conundrum
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> G4JNT> Both coils were the same diameter, same inductance, and roughly 
> the same length in total.   So why was the one made of plain 
> wire better ?   Self capacitance ?    

Gamal> No. Unless the "capacity" exhibits significant dielectric losses, 
> great self capacitance does not harm in lieu of Q.
> What you probably have missed is to keep distance between
> individual turns of the coil's winding. The effect of closely
> winded turns is named proximitty effect. Current in one turn
> tends to displace the current in the adjacent turn and vice versa.

> When constructing loop antenna windings, I try to keep a clearance
> of at least 2 times the wire diameter in between individual turns and
> always get optimum Q. For solenoid type of coils I recommend a minimum 
> of 1 wire's diameter of clearance.
> As the self-made Litz wire has a greater outer diameter, it's
> relative close proximitty to the next turn reduces Q much more
> than in the case of the solid wire.

I use a 400uH commercial variometer in series with my main loading 
coil for tuning. This single layer solenoid coil is wound with Litz 
wire and the spacing is about 1.5 wire diameter.

The main loading coil is wound on plastic fencing material formed 
into a cylinder. It was not possible to maintain a one wire spacing 
so I compromised and wound the coil in 'bunches' of 10 windings.

A lot of effort goes into the design of professional LF coil design, 
to reduce adjacent wire proximity while retaining a managable small 
size as can be seen in the design of the Decca transmitter coil 
formers (hopefully, more will be reveilled when I can figure it out). 
Fairly complex coil design articles appeared in early publications, 
which described basket and honeycomb winding patterns.
I will try to get some of this into the next edition of the LF Book - 
the main problem is the illustrations!


-- 
Regards, Peter, G3LDO

<g3ldo@zetnet.co.uk>