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Re: [TowerTalk] Ferrite beads for common mode current

To: "Mark" <n2qt@arrl.net>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] Ferrite beads for common mode current
From: "jeremy-ca" <km1h@jeremy.mv.com>
Date: Wed, 25 Jul 2007 21:48:49 -0400
List-post: <mailto:towertalk@contesting.com>
On higher HF and 6M simply winding all the turns in one direction adds a lot 
of capacitance which defeats the effectiveness.
Using RG-142 or RG-303 has been popular for decades on these toroids. Wind 
half the turns in one direction, then cross the toroid and reverse for the 
next half.

There is a lot more to using ferrites at RF than at DC and audio. Without 
adequate test equipmenand understanding the procedures required it is often 
very misleading.

Anyone still having a RadioKit catalog from the 1986-90 era will find a 
wealth of data that I wrote on using ferrites at RF.

Carl
KM1H




Carl KM1H

----- Original Message ----- 
From: "Mark" <n2qt@verizon.net>
To: <towertalk@contesting.com>
Sent: Wednesday, July 25, 2007 9:28 PM
Subject: Re: [TowerTalk] Ferrite beads for common mode current


> I've used RG142 which is Teflon insulated for high power use but  still
> small in diameter (like rg58).
> I find that cutting the jacket off allows it to bend enough to fit a 2.4 
> in
> toroid pretty easily.  I dip
> the completed assembly in the dip-it plastic stuff (normally used to put
> grips on tools) to seal it.
>
> Mark n2qt
>
> ----- Original Message ----- 
> From: "jeremy-ca" <km1h@jeremy.mv.com>
> To: <n7ka@comcast.net>; "TowerTalk" <towertalk@contesting.com>; "Jim Lux"
> <jimlux@earthlink.net>
> Sent: Wednesday, July 25, 2007 9:05 PM
> Subject: Re: [TowerTalk] Ferrite beads for common mode current
>
>
>> 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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>>>
>>
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