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Re: [RFI] Several USB cables - single toroid

To: rfi@contesting.com
Subject: Re: [RFI] Several USB cables - single toroid
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 20 Feb 2024 21:09:17 -0800
List-post: <mailto:rfi@contesting.com>
On 2/20/2024 6:12 PM, K9MA wrote:
One problem I can see with several cables through one core is that the currents in the wires may be out of phase, rather that true common mode. Imagine the two halves of a zip cord dipole meeting at the core, then passing through it as a transmission line. The currents would just cancel each other out, resulting in no flux

What you're describing is out of POLARITY, not Phase. Polarity has two values, is the positive or negative sense of a waveform, which gets reversed by turning around the wires or running the signal through an inverting stage.

Phase is a continuous function, measured in degrees or radians, it's different for every frequency. So yes, it's quite likely that common mode current (which is determined by the rest of the antenna that each is a part of) are varying degrees out of phase with each other. And yes, it's a very good reason not to wind multiple cables through the same core.

73, Jim K9YC



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