[TowerTalk] choke / balun design needed

[Jim Brown]

As far as I know, Fair-Rite is the only manufacturer of this material, 
which they developed around 2001. They sell through at least a half 
dozen distributors. Ham distributors, like kitsandparts are notoriously 
expensive, but they do sell onesey-twosey. FAR better to go to one of 
the mainstream industrial vendors and buy in quantity. My current 
favorite for quantity purchases is Dexter Magnetics, near Chicago. I've 
also heard good things about Lodestone Pacific.

To build quantity, combine your needs with those of other local hams who 
are active on the HF bands. I've both organized group purchases and 
participated in group purchases organized by others. See Appendix One of 
my RFI tutorial for some specific advice. k9yc.com/RFI-Ham.pdf  You do 
NOT want to re-ship ferrite cores -- it's expensive and they break.

The last time I bought medium quantity (about 50) of #31 2.4 cores, I 
paid about $5, including the cost of tax and shipping.

73, Jim K9YC

On Tue,4/28/2015 7:47 AM, Alex Malyava wrote:
> Hi Jim,
>
> Do you have any recommendation on manufacturer/part# for 2.4" #31 cores?
> Fair-Rite part # for this core is #2631803802.
>
> mouser.com 
> <http://www.mouser.com/ProductDetail/Fair-Rite/2631803802/> and 
> parts.arrow.com 
> <http://parts.arrow.com/item/detail/fair-rite-products/2631803802#nQpJ> both sell 
> them under that exact part #
>
> What about FT240-31 cores (http://toroids.info/FT240-31.php) that 
> kitsandparts.com <http://kitsandparts.com> sells?
> Is it the same or I should stay away from it?
>
> Thanks,
> Alex K2BB
>
> On Mon, Apr 27, 2015 at 12:41 PM, Jim Brown <jim at audiosystemsgroup.com 
> <mailto:jim at audiosystemsgroup.com>> wrote:
>
>     On Mon,4/27/2015 6:50 AM, Alex Malyava wrote:
>
>         What would be the bestest design for choke or balun to be used
>         with dipole
>         or OCF dipole?
>         Like what type of core, number of turns or number of beads?
>
>
>     k9yc.com/RFI-Ham.pdf <http://k9yc.com/RFI-Ham.pdf>
>
>     See the Choke Cookbook and text that precedes it.
>
>     An off-center fed antenna is inherently poorly balanced, so it
>     puts a high common mode current on the feedline, which in turn
>     places a high common mode voltage across any choke. It is well
>     known that even very good common mode chokes are likely to fry
>     (fail destructively) when used with even moderate power levels.
>     You MIGHT get away with it at 100W, but at some higher power level
>     it WILL break.
>
>     73, Jim K9YC
>
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