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Re: [TowerTalk] Ferrites 31 vs. 77 material

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Ferrites 31 vs. 77 material
From: Jeff Blaine <KeepWalking188@ac0c.com>
Date: Sat, 9 Nov 2019 13:36:12 +0900
List-post: <mailto:towertalk@contesting.com>
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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