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Re: [TowerTalk] Ferrites 31 vs. 77 material

To: <towertalk@contesting.com>, "Jeff Blaine" <KeepWalking188@ac0c.com>
Subject: Re: [TowerTalk] Ferrites 31 vs. 77 material
From: "Bob Shohet, KQ2M" <kq2m@kq2m.com>
Date: Fri, 8 Nov 2019 23:46:02 -0500
List-post: <mailto:towertalk@contesting.com>
Thank you Jeff – that was easy to understand and most helpful!

73


Bob  KQ2M


From: Jeff Blaine 
Sent: Friday, November 08, 2019 11:36 PM
To: towertalk@contesting.com 
Subject: Re: [TowerTalk] Ferrites 31 vs. 77 material

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@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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