Hi Warren

I obtained a large powdered iron core ring (of uncertain pedigree), about
5inches diameter from either one of the Decca sites or from Rugby before it
closed down. On this I wound about 12 turns of 12SWG wire tapped at every
turn to make a multi-ratio auto transformer to match the Decca transmitter
to the bottom of the loading coil. This handled around 7amps to the antenna
when the Decca was on full power and  the core and windings just became
slightly warm after a couple of hours operation.

73

Peter G3LDO

 My loop has a step down transformer from 50 ohms to the loop impedance of

about

1.7 ohms. I've implemented this with 4 stacked FT-290-77 ferrites and 16

turns

of #10 teflon for the 50 ohm side and 3 turns of some european 16mm2

rubber

insulated wire for the low impedance loop side of the transformer. The
transformer and resonating caps are mounted in an fiberglass electrical
enclosure outside. The core does heat up - to the point where I've been

leaving

the door to the enclosure open (not good!)   I know that if I increase the

turns

on the loop side I'll decrease the magnetic flux density and hence reduce

the

core heating. However, the windings themselves appear to heat up a little
independent of the core heating. I'm reluctant to go to smaller gauge wire

and I

can't fit any more turns on the existing core. I've found a powdered iron

core

T-520-52 that seems like it might do the trick. The mix 52 material is a

lower

loss version of the Mix 26 material. The permeability is high enough so

that I

can get enough inductance on the 50 ohm side with a reasonable number of

turns.

(Using the rule that inductive reactance of the primary is at least 5x the
source impedance of 50 ohms).  Does anyone have any experience with

powdered

iron cores at high power? Any thoughts on this problem?
Thanks & 73
Warren

--
73 Warren K2ORS/WD2XGJ
FN42hi
http://www.w4dex.com/wd2xgj.htm