[TowerTalk] Ferrites 31 vs. 77 material

[Jeff Blaine]

A single turn through a given core has much less Z than the multi-turn 
variety.  And as frequency goes down for a given ferrite (of any type), 
the Z is also lower.

So it's not that they only work at VHF, it's that the contribution to Z 
is pretty small, especially on HF.  Which is why you see that sleeve 
type chokes need a LOT of ferries to provide anywhere a reasonable 
choking Z.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com


On 11/9/19 1:01 PM, Bob Shohet, KQ2M wrote:
> Hi Jim,
>
> Thank you for your reply and the link to your extremely comprehensive documentation!  I read though it at length today and there was much that I did not understand very well.  I am going to read it again over the weekend.
>
> You mention that the bead only works at VHF but I did not recall seeing anything addressing that.   Is it that the choking resistance is not great enough or is there some other reason(s)?  Could you please explain?
>
> Tnx & 73
>
> Bob  KQ2M
>
>
> From: Jim Brown
> Sent: Wednesday, November 06, 2019 10:52 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Ferrites 31 vs. 77 material
>
> On 11/6/2019 6:28 PM, Bob Shohet, KQ2M wrote:
>> I prefer to use large ferrite beads that fit on the coax – roughly 1/2” ID -  1” OD  x 1 1/4” height and then tape the beads in place in physical proximity  to each other next to the feedpoint.
> You may prefer that, but that sort of bead only works at VHF. My
> detailed recommendations are here. http://k9yc.com/2018Cookbook.pdf
>
> Yes, #31 material is the weapon of choice for 160M - 6M.
>
> 73, Jim K9YC
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