Hello all
recently I asked some coil winding questions.
Now I am able to answer them to some extend by myself:
GS> (1) How do I form a low loss coil for 137 kHz
GS> using mentioned 2mm annealed copper wire?
One solution would be to use single layer solenoid instead
of multiple layered ones. This however is not feasible with
2mm annealed copper wire as the length dimension gets
too large, especially if (3) is taken into account.
GS> (2) Shall I use other form factor?
From LOFERS scratch book I draw some information about
coil winding scheemes.
The "doughnut shape winding" is regarded to as to provide relative large
inductivity for the volume. This is a multi-layered solenoid with short
length but high flanges. Actually the original antenna winding was
designed in this way ! Using my 2mm wire would end in tremendeous
height of the flanges, the coil would more look like a disk rather than a
doughnut.
The "honeycomb winding" scheeme is good for relative low inductivity
(as would be required for HF rather than LF), low loss and low
winding capacity. The turns of the wire are not aligned side by side
as with usual solenoids instead, running from left to right while doing one
turn.
This provides for much space in between adjacent wires and adjacent
layers. Again the resultant dimensions and volume would be tremendeous
with my wire and required inductivity.
Former winding scheeme can be modified for larger length and moderate
height. This would be a transition in between "honeycomb winding" and
"Basket weave winding", which has large inner diameter for the bobin,
small height (flange, actually a single layer structure) and moderate
bobin length. Again relative low losses are combined with low
winding capacity.
GS> (3) Shall I use greater distance between wires?
This appears to be the key to solve my problem. When I made
the alternative antenna coil winding, I was aware of the
skin effect. The original wire size (0.335 mm) was already the
maximum diameter for avoiding skin effect (skin depth for
copper at 137kHz is about 0.18 mm).
When 0.335 mm diameter wire has a circumference of roughly
1 mm, the 2 mm diameter wire has one of 6.3 mm. This would
result in a 1:6 benefit regarding skin effect losses - for a single wire!!
What I did not take account for is the proximity effect. The original
wire had a silk spun coating over the copper strands (or even litz?),
my 2 mm (solid) wire only the lacquer coating. Winding my 2 mm
wire side by side results in (relative) closer proximitty between
wires as compared with the original 0.335 mm wire.
As an intermediate conclusion I should find the optimum by
keeping at least one wire diameter spacing in between turns
as well as from layer to layer. Something in between honeycomb
winding and basket weave winding with doughnut winding form factor
using a moderate large wire diameter (less than 2 mm :-) could
probably bring me closer to the wanted low-loss coil.
Further ideas are welcome.
Best 73
Gamal Soegiono (SWL)
50N01 / 08E27 / JO 40 fa
[email protected]
| 