[ARC5] BC-230 mic

[Dennis Monticelli]

With all respect, I don't think that is true.  If the skin depth is well
below the thickness of the shield, then the inner currents and outer
currents do not mingle nor do their fields couple.  If it were true then
wrapping the coax around and through a torroid would wreak havoc upon the
normal differential currents carried with that transmission line.  And we
know that doesn't happen.

I like to think of coax as a three wire cable.  What goes on inside is not
effected by what goes on outside and vice versa....if the shield is thick
enough and conductive enough to do its intended job.

Balanced two-wire transmission line is easier to understand conceptually
and can work well (I use it) but keeping everything in balance so its
common-mode rejection is decent is a real challenge.  The antenna, the
line, it's immediate environment and the tuner or matching network must all
be in balance.  Not easy in a real world environment.  If one cannot create
that balance, one may be better off with well-shielded coax, despite the
higher loss.

Dennis AE6C

On Mon, Nov 10, 2014 at 10:37 AM, AKLDGUY . <neilb0627 at gmail.com> wrote:

> Hi Dennis
>
> Well yes, but an even simpler explanation is that because radiated hash is
> picked up only by the braid, the opposite polarity of that hash voltage
> appears
> on the coax inner wrt the braid. So in effect, the inner carries into the
> receiver
> whatever the braid picked up.
>
> 73 de Neil ZL1ANM
>
>
>
> On Tue, Nov 11, 2014 at 3:49 AM, Dennis Monticelli <
> dennis.monticelli at gmail.com> wrote:
>
>> Another way of putting it is the differential signal is protected by the
>> coax shield from the intrusion of noise but any common mode noise flows
>> right down the outside of the braid into the receiver and makes the circuit
>> common (usually the chassis) hot with noise.  If the receiver has very good
>> common mode rejection (i.e. an excellent RF ground) then no problem but in
>> most cases that is not true.  This is why common mode chokes are so popular.
>>
>> Dennis AE6C
>>
>>
>>