[TowerTalk] current balun question

[Roger (K8RI) on TT]

Doesn't the added inductance of a choke that covers 80, or 40 also add 
more than just the length of the coax?

73, Roger (K8RI)


On 3/9/2017 4:57 PM, Jim Brown wrote:
> On Thu,3/9/2017 1:47 PM, Dave Clemons wrote:
>> I am suspicious that doing so would cause the coax lines on the 
>> parasitic elements to no longer be the proper length for 153.45 degrees, 
>
> Yes
>
>> acting sort of like a loading coil.
>
> No, but screwing up the phasing. Putting it simply, the total length 
> of coax in each feed must be that 153.45 degree length, including any 
> coax that you coil up.
>
>> Am I correct to assume this would be a bad idea?
>
> Yes, for that reason and also because a coil of coax is NOT an 
> effective "current balun." What's often called a "current balun" is 
> really a common mode choke. Study k9yc.com/RFI-Ham.pdf to understand 
> why that coil of coax is a lousy common mode choke, and to see several 
> options for GOOD common mode chokes in the Choke Cookbook.
>
> 73, Jim K9YC
>
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-- 

73

Roger (K8RI)


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