Topband: Ferrite Cores

[Charlie]

Well, I don't think there is a "one-size" or "one--mix" "fits all" preferred
solution. I've wanted to try some 31 mix cores for common-mode isolation at
80 and 160.  On the other  hand, some of the Fair-Rite 71 (73?) material
toroids and binocular cores provide really good performance, even at lower
frequencies, because of the lower losses and better frequency response.

I also suspect that for power handling applications ( including common-mode
suppression), the 31 mix might have some heating issues, because of the
higher losses.

BTW, I do know from experience that the  Fair-Rite 71/73 etc. mix higher
frequency cores seem to be impervious to weather!  I have  used the tubular
cores and large binocular cores out of doors for years as common mode chokes
on RG-213 for my 5-band quad feed-line and to make quick home-brew W2DU 1:1
current baluns for vertical dipoles for. 30 and 40 meters. I've never seen
any evidence of corrosion nor have I  noted any performance degradation.
I've used the binocular transformer cores to construct matching transformers
for "KAZ" terminated receiving loops for 160.80.40 and 30 m and  use a
larger binocular  core to match 50 ohms up to the cathode impedance of my
home-brew 3-500ZG amp, to avoid  having to install a much more complex
band-switch. Works quite well 160-10m and comfortably handles everything
that my FT-1000MP delivers.

Fortunately I had a good selection of cores in my Fair-Rite developer kits
from my engineering days!

73,
Charlie, K4OTV



-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Tom W8JI
Sent: Wednesday, August 06, 2014 3:09 PM
To: Ron Stordahl, AE5E; topband at contesting.com
Subject: Re: Topband: Ferrite Cores


In this discussion two different ferrite mixes are mentioned: #31 and #61.


>From the descriptions of these on the Fair-Rite web page, it appears that 31
would be more suitable for lower frequency applications. >>>>

Core selection can be fairly complex in transmitting systems. I've yet to
see a case where one core mix is the be all end all for the range of things
you run into in the field. Especially at high common mode impedances.

Receiving is a completely different story, because core stresses are always
low.

73 Tom


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