[RFI] Common Mode Noise?

Jim Brown jim at audiosystemsgroup.com
Wed Jan 22 14:09:00 EST 2025


On 1/22/2025 10:43 AM, K9MA wrote:
> The whole point of using coax is to prevent radiation until the RF gets 
> to the antenna. There's no need to further complicate the issue.

There is no more or less radiation from a 2-wire line than from coax. 
What causes radiation is common mode current, and 2-wire can carry just 
as much common mode as coax of the total antenna system is unbalanced. 
Just as in coax, common mode current in 2-wire line shows up as a 
difference between current in the two wires, taking both magnitude and 
phase into account.

Antennas can be unbalanced by their surroundings, like variable height, 
sloping ground, nearby conductive objects, imbalance in the termination 
of 2-wire line in the shack, including a poorly balanced tuner or 
matching network.

73, Jim K9YC



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