[TenTec] OT: SWR & Coax

[Dr. Gerald N. Johnson]

On Mon, 2008-07-07 at 10:57 +0200, shristov wrote:
> Basic facts of physics are as follows.
> 
> 1. Whenever an AC current flows, there is radiation.
>     There are no exceptions. Also, there are no additional conditions.
>     All that is needed is an AC current flowing.
> 
> 2. The only way to "prevent" radiation is to counteract it by a radiation
>     from another AC current of the same magnitude and opposite phase,
>     flowing in a nearby conductor.
>     This is how transmission lines work, both "coaxial" and "open".

No. The shield of the coax can have independent currents inside and
outside. It takes a load like an antenna to cause currents on the
outside. The shield prevents radiation from the inside current even if
it doesn't match the magnitude and opposite phase from the center
conductor.
> 
> 3. If the cancellation mentioned above is not complete (unequal magnitude,
>     inexact phase, separation too large) the transmission line will radiate.
>     This is what happens with "unbalanced" lines, carrying "common mode"
>     currents in addition to normal "differential mode" currents.

Not with coax, because its shielded and the fields are enclosed.
> 
> 4. This has nothing to do with SWR.
>     SWR is a completely different phenomenon.
>     It neither enables nor prevents radiation.
> 
> 
> 73,
> 
> Sinisa  YT1NT, VE3EA
> 
73, Jerry, K0CQ