Re: LF: HF Litz wire for TX coils?

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Yes please don't burn down the institute Stefan!

73s
Roger G3XBM

2011/8/30 Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>

LF,

I plan to build a rather compact LF TX coil with reduced losses. Now i
think about using a bigger enamelled wire (currently using ordinary
loudspeaker cable). A local distributor (http://www.elnatrafo.de/)
offers 2mm diameter enamelled copper wire for about 10 EUR/kg which is a
fair price. The current wire is 0.75mm^2, so about 1 mm diameter.

HF Litz wire may have lower losses at 136 k but what about the current
capability / ampacity? I searched for some data of the litz wire i used
for the ferrite antenna: A litz wire of 120*0.1 mm
(http://www.reichelt.de/index.html?ACTION="">SEARCH=CLI%20200%2F120)
is 0.943 mm^2 but handles just 3.36 A.

A single wire with 2mm diameter (assuming 0.18mm skin depth at 136 kHz)
has a effective cross section area of 1.02 mm^2, so about the same as
the Litz wire i mentioned. But the single wire is more robust, cheaper
and easier to wind. Also the heat transfer could be better with a single
wire when using a PVC tube for the coil.

I need about 2.9 mH for resonating at 137 kHz  (yes, Mal, we know, you
have below 1 mH our youzr inv-L). This could be achieved by using a 20
cm diameter tube and about 120m of wire. http://dl.dropbox.com/u/19882028/LF/coil%20calculation.png

Any comments or suggestions?

73, Stefan/DK7FC

PS: What do you think about a coil body out of glass? I have to take
very special care here not to burn down the institute but i want to
remote control the system, so mostly i cannot watch the coil and have no
XYL walking arround in the garden, telling me if something begins to
smell ;-)

-- 
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/