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Re: [TowerTalk] [RFI] Snap-on Ferrites

To: towertalk@contesting.com
Subject: Re: [TowerTalk] [RFI] Snap-on Ferrites
From: kc4pe <kc4pe@bellsouth.net>
Date: Mon, 19 Jun 2017 07:57:32 -0400
List-post: <mailto:towertalk@contesting.com>
Chris:

Clarify: When your talking about turn in a snap 0n your referring to the large snap, 1.75 X 2.25 with a .75 opening, not the 1.255 X .75 with a .312 (5/16_ opening..?

So inquiring minds wonder when you buy a printer/TV set, etc and there is a molded Ferrite block on the AC line. what are they trying to block..??

So when the Ham says .."Hey I got rid of my RFI on my TX signal by clipping on three blocks of ferrite..."

And what about the Ham at the show that was selling ferrite snap ons (small) with a blue and red labels with bold arrows printed on the black label? What coulkd the arrow mean??

Thanks,


-Bill .. KC4PE


On 6/18/2017 11:11 PM, EZ Rhino wrote:
I think what he (the author) means is this:

  A snap-on, without multiple turns through around it, isn't effective at HF 
frequencies.  We're talking about mix 31 or 43 here.  If you wind multiple 
turns around the snap-on (assuming you pick a size large enough to do so for 
the cable you're trying to choke) then the choking frequency goes down (to HF 
range) and the impedance goes up, which is what you want.  So it's not the 
snap-on that is the problem, it is how you are using it.  If there was such a 
thing as mix 73 snap-on that was large enough, then that would work as a string 
of beads choke (because it is effective at HF).  But it would take a lot of 
them, say 50, to get the proper amount of choking impedance.  A single snap-on 
just don't have enough umph.

Hopefully I worded this technically correct.

Chris
KF7P


On Jun 18, 2017, at 20:44 , <john@kk9a.com> wrote:

I was reading the recent QST article RF Mayhem by WB8IMY. The author said to
avoid using snap-on ferrites for problems caused by HF signals as they
rarely work well at HF. It is best to stick with circular cores.

Is this correct?  I was not aware that snap-ons were less effective.

John KK9A

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