[TowerTalk] Common-mode choke

[TexasRF--- via TowerTalk]

Jim, trying to understand the source of the high resistance that is  
frequently mentioned for choke design.
 
I can see one scenario where a series to parallel conversion might explain  
it. Say 400 ohms xl in series with 20 ohms R would transform to 8020 R in  
parallel with 401 ohms xl. Added shunt C would increase the effective xl up 
to  the point of resonance.
 
Is this a possible explanation of the fundamentals?
 
Thanks/73,
Gerald K5GW
 
 
 
 
 
 
 
In a message dated 5/20/2014 8:02:27 A.M. Pacific Daylight Time,  
jim at audiosystemsgroup.com writes:

On  5/20/2014 7:05 AM, Jim Thomson wrote:
> if any choke is high resistance,  it will work..provide the Z is sky high.
> Power is still I squared x  R.

Yes. I have shown in my tutorial why choking Z on the order of 5K  ohms 
resistive is a suitable design goal for most installations, and W8JI  has 
reminded us of some where that's not enough. The only string of beads  
choke material that can get anywhere close to 5K on HF is the #73  
material that W2DU chose, and you need several hundred of them to get  
there. You would need that higher value for the high power amps you like  
to use. The largest #73 material bead is just large enough to fit coax  
like RG303. There's a discussion of his choke in the two referenced  pdfs.

73, Jim  K9YC

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