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[TowerTalk] Common-mode choke

To: <towertalk@contesting.com>
Subject: [TowerTalk] Common-mode choke
From: "Jim Thomson" <jim.thom@telus.net>
Date: Tue, 20 May 2014 07:05:35 -0700
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Date: Mon, 19 May 2014 23:54:57 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Common-mode choke

On 5/19/2014 6:19 PM, Jim Thomson wrote:
> use 2 foot of the large diam type 43 beads  slid over  213u  or  393 coax.

Sorry, Jim, but string of bead chokes using #31 or #43 simply are not 
very effective on the HF bands because their resonance is at VHF, and 
their resistive component at HF is very low. Study k9yc.com/RFI-Ham.pdf 
to understand why resistance is good and inductive reactance is bad.

73, Jim K9YC

##  per steve hunts charts, they, bead baluns, depict a large resistive 
component. 
Thats his black line on each chart. 

##  if any choke is high resistance, it will work..provide the Z is sky high. 
Power is still I squared x R. 

##  If you really wanted a sky high Z... a physical  quarter wave of coax...
or a  3 quarter wave of coax.....  minus 2-3%.... with the braid bonded to
the top of the tower, works extremely well.  Then no ferrite required at all. 

##  The fellow wanted a choke balun for the 10M band.    24 inches worth of 
large diam
beads slid over 213 or 393 will easily suffice on 10m band. 

##  4 turns of 213 u  around 4 x 2.4 inch od  type 31 cores will also work.

##  If its just a 10m yagi on a tower....a  physical quarter wave.. minus 2-3 %
will do the job very readily. 

Jim   VE7RF  

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