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Re: [TowerTalk] Balun Recommendation

Subject: Re: [TowerTalk] Balun Recommendation
From: Jim Brown <>
Date: Mon, 16 Apr 2012 09:16:13 -0700
List-post: <">>
On 4/16/2012 4:11 AM, Jim Thomson wrote:
> 22 x  type 43  beads, of the  1.125 inch long x 1 inch diam  x .515 inch ID   
> variety, slid over RG-213 or  RG-393 coax will also work.

Jim, you are looking at the elephant through a pin hole.  You build and 
run big power amps, and your measure of the effectiveness of a choke is 
that there it doesn't blow up.  A string of beads on coax that are not 
lossy at the operating frequency CANNOT overheat -- there's not enough 
resistive component to their impedance to dissipate power -- but they 
are also essentially useless for all of the reasons outlined in my RFI 

The primary function of a common mode choke in an antenna that is used 
for receiving is to MINIMIZE RECEIVE NOISE, and to do that effectively, 
the choke must have a high resistive common mode impedance at the 
frequency(ies) of interest.  Ferrite chokes operate as parallel resonant 
circuits. A single turn through cores made of #31 and #43 ferrite 
materials is resonant around 150 MHz, so it is USELESS on the HF bands. 
To be useful on the HF bands, we must wind multiple turns through the 
material to increase both the inductance and the stray capacitance so 
that the resonance moves down to the frequencies where we want to use 
them.  Until you understand that fundamental concept, you are going to 
continue to make incorrect assessments of the value of various 
solutions.  I refer you to my RFI tutorial, which addresses the 
technical issues in detail, including an analysis of dissipation at high 
power levels that doesn't "hide behind the math."

73, Jim Brown K9YC

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