Yes Paul,
There is a lot more to it.
Usually you find that a core usable for higher frequency has a a lower u and
therefor also a lower Al. More important is the "mix". The magnetic hysteresis
losses are varying, beside the amount of saturation you decide to allow,
depending the "mix". You also have eddy current losses depending conductivity
and grain size (iron powder cores) of the "mix".
The easiest road is to follow the manufacturer's recommendations. Another way
to go is to experiment, especially if you have a shoe box full of various,
unknown cores. (that's usually my way:-).
I find the larger cores being easier to deal with as you have plenty of room
for wires and plenty of cooling surface to remove unwanted heat. Just remember
when you test the cores that you make sure you really are putting your
contraption to work. Making a current transformer (or common mode choke) test
by attaching a transmitter on one side and a dummy load on the other doesn't
test the ability of the transformer/choke to suppress common mode current.
Adding a wire between the shield on one side of the transformer/choke and the
center lead on the other will do a better test.
Myself, I am using a air wound coil, 40 turns of RG58 on a 4 1/2" D, 6" L
cylinder as the choke. No, it is not hanging in free air but is well supported.
End up to work well from 1.8 to 60 MHz. Has a Z=500 Ohm at 1.8 MHz and 60 MHz.
Best 73 de,
Hans - N2JFS
-----Original Message-----
From: Paul <radioboy@telus.net>
To: 'Richard (Rick) Karlquist' <richard@karlquist.com>; towertalk
<towertalk@contesting.com>
Sent: Wed, Oct 29, 2014 8:50 am
Subject: Re: [TowerTalk] 4:1 balun questions KT-34XA
Further reading...
Looking at Fair-Rite catalog of toroids, mix 61 which seems to be very
popular and recommended for HF baluns, has a mu of 125, and Al (nH/T2) of
170 for a 2.4" dia core. The Arnold MPP core, which is Nickel-Iron-Moly has
same 125u and Al of 155 for a 2" core. I'm not sure what else would make
one better than the other...there must be more to it though.
Help
Paul
-----Original Message-----
From: Richard (Rick) Karlquist [mailto:richard@karlquist.com]
Sent: Tuesday, October 28, 2014 10:22 AM
To: Paul; towertalk@contesting.com
Subject: Re: [TowerTalk] 4:1 balun questions KT-34XA
Your choice of MPP is very unorthodox.
MPP = moly permalloy powder.
Generally, ferrite is used for baluns.
It is also used for some tuned circuits but powered iron has some advantages
for tuned circuits and is often used in that application. I've never seen
MPP used for RF. Can you tell us why you chose MPP? How is it different or
similar to "powdered iron"?
73
Rick N6RK
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