It aint easy getting 5 turns of RG-213 thru a 2.4" OD dia toroid!
The definitve tests for Fairite 43 Mix beads as a sleeve balun was done in
the early 80's and published in Scuttlebut and most likely reprinted
elsewhere.
Carl
KM1H
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: <n7ka@comcast.net>; "TowerTalk" <towertalk@contesting.com>
Sent: Wednesday, July 25, 2007 8:12 PM
Subject: Re: [TowerTalk] Ferrite beads for common mode current
> At 01:58 PM 7/25/2007, n7ka@comcast.net wrote:
>>Getting ready to install another 6M yagi here and building another
>>for a friend. Want to use a choke on the feed line which will be
>>either RG-213 (MIL-C-17 compliant) or on LMR-400UF (super flex). In
>>all cases I want the capability for 1500W. I do not like the idea
>>of additional connectors so my plan is to but the beads on the line
>>at feedpoint of the cable that goes down to the hardline just below
>>the top of the tower. Would Fair-Rite 2643102002 be the correct
>>choice? The id at 0.505 inch is large enough to fit over the
>>RG-213/LMR-400. Or do I need another mix and how many beads.
>
>
> You can also use a larger diameter toroid and run multiple turns of
> your coax through it. The inductance of the choke goes as the square
> of the number of turns, so 5 turns through one core is like 25 cores
> in a row (in an ideal world... there's capacitance and leakage L...
> but still... )
>
>
> Jim Brown's website http://www.audiosystemsgroup.com/ has a paper on
> various ways to make RF chokes for feedlines (among other things)
> with measured data over a wide range of frequencies. It's that
> RFI-Ham pdf file referenced in recent posts. 5 turns on a #31 2.4
> inch core looks like around 1Kohm Z.. (see page 12) page 28 has a
> photo of a mondo choke. I use one very similar to this for
> connecting a network analyzer to antennas (except I use smaller coax).
>
> Jim, W6RMK
>
>
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