Envelope-to: dave@picks.force9.co.uk
Delivery-date: Thu, 09 Feb 2006 22:43:07 +0000
From: Warren K2ORS/WD2XGJ <k2ors@comcast.net>
To: rsgb lf reflector <rsgb_lf_group@blacksheep.org>
Date: Thu, 09 Feb 2006 22:41:40 +0000
Message-Id: <020920062241.10576.43EBC52300092A360000295022007456720B97010D0A020E06979D0E03@comcast.net>
Subject: LF: Powedered Iron Cores for high power?
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Question for  the list members,

 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