On May 13, 2005, at 9:32 AM, Stephen W. Kercel wrote:
Comment on baluns: If you drive a ferrite core to saturation, it
will overheat.
True.
Once the core overheats, the inductance changes and you lose your
match (quite severely, in my experience).
In order to change the inductance permanently, it must reach the
Curie temperature. The inductance will change much at a much lower
temperature than this, but the effects aren't lasting.
It doesn't really take much to do it; a few minutes of normal CW
operating with 100 watts into a 5:1 SWR on 20 meters will do the
trick for me. You are much more likely to drive a balun core into
saturation on the high SWR output of a tuner than on the low SWR
input of the tuner.
Note that a normal current-type balun feeding a non-pathological
antenna (one that has made a reasonable attempt to be balanced) will
show little or no flux on the core. The object of the current-type
balun is to discourage current from flowing by creating a high-
impedance path -- if there's high impedance there's little current
and therefore less chance of heating.
Bill Coleman, AA4LR, PP-ASEL Mail: [EMAIL PROTECTED]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
