[RFI] Several USB cables - single toroid

[K9MA]

On 2/20/2024 11:09 PM, Jim Brown wrote:
> 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

Polarity is just a simple case of 180 degrees out of phase.

-- 
Scott  K9MA

k9ma at sdellington.us