[RFI] Fw: Re: Ferrite Beads
Jim Brown
jim at audiosystemsgroup.com
Thu Jan 5 12:01:01 EST 2006
On Thu, 05 Jan 2006 00:55:43 -0800, Dennis V wrote:
>I just got some #31 mix from DX Engineering but have not had to
>use them ...yet.
I suspect they are using them because I published all my info about the new mix.
>Are there any FT240-31 available from anyone.
Yes.
Expect to pay < $4 for the toroids from a distributor. The first price break is at 250
pieces. It won't be called FT240-31, because that's an "artificial" part number cooked
up by an individual distributor to hide the real part number (so they can sell at a a
3X markup). The real Fair-Rite part number for the FT240 form factor is 26nn803802,
where nn is the mix.
Another Fair-Rite part that I find very useful for HF is 0431177081 -- a lot more
expensive, about $11 each in small quantities. See the app note for measured data and
a photo. I suggest you buy a dozen or so if you're active on HF. I clamped 8 of them
around the power feeders (a twisted triplet) to my house, and it has reduced some of
my line noise. Note that you can't do this to individual conductors, only to all of
them, because the current on individual conductors would likely saturate the ferrite
(and could overheat it).
Go to the Fair-Rite website and see the list of distributors. I've had excellent
service from Kreger, and strongly recommend them. Don't "nickel and dime " them though
-- they mostly sell in hundred and thousand lots, so give them an order for at least a
dozen of each part. You will also pay for shipping -- these things are heavy, so I use
UPS ground. Since you're on the west coast and shipping is based on distance, you
might save a few bucks by using a west coast distributor. My CA ham friends have used
Lodestone Pacific.
Jim
>73, Dennis, N6KI
>At 02:40 PM 1/4/2006, you wrote:
>>Hi Dennis,
>>
>>See the tutorial app note on my website for measured data on the #61
>>material, as
>>well as my general and specific guidelines for when to use it.
>>
>>The executive summary is that #61 is useful for suppression only at high
>>VHF and
>>above, because it has far too little loss below low VHF. Because of that low
>>loss, #61 makes an excellent core for transmitting baluns in the 100 watt
>>range.
>>There's a famous DXer and excellent EE (W1-call I've forgotten) who's written
>>about a family of baluns using #61 2.4" O.D. toroids (called FT-240-61 by
>>resellers).
>>
>>#31 is the new champ for RFI suppression. Again, see the app note on my
>>website
>>for details. www.audiosystemsgroup.com/publish
>>
>>73,
>>
>>Jim
>>
>> On Wed, 04 Jan 2006 13:01:35 -0800, Dennis V wrote:
>>
>> >Jim,
>>
>> >I was reviewing thread of mail on materials used in Ferrite beads/Toroids
>>
>> >What can you tell me about 61 mix material and at what freqs would a 2.4"
>> >donut be most effective?
>>
>> >73, Dennis N6KI
>>
>>
>> >>X-UNTD-OriginStamp: dp8reD5dz1WVmgQsod6THYeoyfSELxGmHp7RpQlZXRw=
>> >>To: n6ki at earthlink.net
>> >>Date: Sat, 23 Oct 2004 12:49:23 -0700
>> >>Subject: Fw: Re: [RFI] Ferrite Beads
>> >>X-Mailer: Juno 4.0.11
>> >>From: n6ki at juno.com
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>> >>
>> >>
>> >>
>> >>--------- Forwarded message ----------
>> >>From: "Jim Brown" <jim at audiosystemsgroup.com>
>> >>To: "rfi at contesting.com" <rfi at contesting.com>
>> >>Date: Mon, 18 Oct 2004 19:52:03 -0500
>> >>Subject: Re: [RFI] Ferrite Beads
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>> >>
>> >>On Mon, 18 Oct 2004 17:30:41 -0400, Tom Rauch wrote:
>> >>
>> >> >The recommended beads are 31 or 73. The problem is in a
>> >> >large size 31 and 73 have internal resonances when the
>> >> >diameter and thickness is large, so you will be stuck with
>> >> >something like a 33 material in large beads. It's only a bit
>> >> >better than 44, but at least it's better.
>> >>
>> >>I have measured a LOT of ferrites, beads and otherwise, and I agree in
>> >>general. BUT: Download and study the EXCELLENT pdf catalog from Fair
>> >>Rite (google to find them), and study the app note on the use of beads
>> >>for
>> >>suppression.
>> >>
>> >>Several points. First, yes, the 31, 73, 77, and 78 mixes are best for 160
>> >>
>> >>and 80. Second, making multiple turns through any ferrite toroid or bead
>> >>will multiply the impedance AND move the effective range of the
>> >>bead/toroid down in frequency a LOT.
>> >>
>> >>Those #43 mix materials that are stinko at 14 MHz with one or two turns
>> >>are quite effective with 3-5 turns. With 8 or so turns, they are
>> >>effective on 80
>> >>and 160 meters, and 10-12 turns makes them effective in the middle of the
>> >>
>> >>AM broadcast band! And when you do multiple turns, the impedances will
>> >>get a LOT higher.
>> >>
>> >>Third, as you do multiple turns, the stray capacitance shorts the choke
>> >>at
>> >>higher frequencies, so a multi-turn choke optimized for 160 or 80 will
>> >>probably be a lot less effective on 15 meters and above.
>> >>
>> >>And finally, to clarify what Tom was saying, it is VERY important that
>> >>you
>> >>operate the ferrite choke in the range where it is hardly a choke at all,
>> >>but is
>> >>primarily resistive. Why? Simple -- any inductance will increase the
>> >>current
>> >>by resonating with the capacitance of the short antenna.
>> >>
>> >>I'm currently at an EMC workshop in CA lectured by Henry Ott, so don't
>> >>have time to say a lot more.
>> >>
>> >>Jim Brown K9YC
>> >>
>> >>
>> >>
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