Re: LF: MF: EbNaut

[Johan Bodin <jhbodin@tele2.se>]

The attached picture shows an autotransformer wound on a a 58mm 
(58/41/18mm) Philips (now Ferroxcube) core made of 3C85 ferrite. The 
transformer was used by SM6PXJ and me at 7S6SAJ in 2000 to bring the ~8 
ohm antenna feedpoint resistance up to 50 ohms at 137kHz. The 
thermocouple meter was calibrated at 12A full scale so there was about a 
kW of power passing through the transformer as the picture was taken.
The winding was made with 2.5 mm^2 flat PVC insulated wire taken from a 
stripped 2-conductor cable intended for 48V DC power in telephone 
exchange equipment (!). There are 3 tinned multi-wire conductors laying 
side-by-side inside the flat PVC without individual insulation. No fancy 
Litz here but the flat geometry may have  helped to reduce the skin 
effect loss.
The transformer was only slightly warm after minutes of key-down at 1 
kW, perhaps 40C, so no fan needed.
73 de
Johan SM6LKM

Paul Nicholson wrote:
> Is it normal practice to need a fan for the toroid?

trafo.jpg
Description: JPEG image