Paul,
As a general rule, when you doubling the core area, which you do when you pile
two cores on top of each other, you will need only about 70% of the turn used
for the single core to keep the inductance at the same value. In the case of 8
turns I recommend 6 turns (5.6 turns are hard to achieve). The magnetic flux
will be reduced by 30% which may lead to a reduction in core losses (if you are
close to saturating the core). You will notice a reduction in temperature as
you will have a larger cooling area.
As you need fewer turns you could use a larger gauge wire, reducing the
resistive losses.
Good luck with your project.
Best 73 de,
Hans - N2JFS
-----Original Message-----
From: Paul <radioboy@telus.net>
To: towertalk <towertalk@contesting.com>
Sent: Tue, Oct 28, 2014 7:46 am
Subject: [TowerTalk] 4:1 balun questions KT-34XA
Hi Guys,
Getting ready to put up my KT-34XA this weekend and just trying to get the
balun right. I have been experimenting this week with cores and windings and
have found a combo that sure looks good on the MFJ-259 and seems to not get
too hot on a soak test...what I have come up with is a core from Arnolds MPP
series which is 125u, 2" diameter and with 8 turns 14ga enamel with
Fiberglas tape spacers, bifilar wound for each half ,on one core, I am flat
from 1MHz-45MHz with the MFJ-259. Running 500W through it for 5 minutes gets
it hot, but I can still hold it. I want to end up winding it on 2 cores,
half on each and am wondering if I should use the same # of turns on each
core as I would if it were a single core, ie 8 turns on each core, then
connect to make it a 4:1, or do I need to modify the turns count when I
split to 2 cores? Also, when splitting to 2 cores, do they need to be
oriented in any particular way or can I stack them one on top of the other,
like 2 doughnuts? The antenna is all rebuilt and tested with my single core
balun....just need some + temps and no snow for the weekend.
Your advice is greatly appreciated.
73
Paul
VE7KHz
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