[ARC5] BC-230 mic

[Dennis Monticelli]

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

On Sun, Nov 9, 2014 at 9:52 PM, AKLDGUY . <neilb0627 at gmail.com> wrote:

> > Not so.  If it is good quality coaxial cable, the outside of the shield
> should be totally isolated
> > from the inside of the shield.  RF (supposedly) does not penetrate the
> shield.
>
> And that is the problem! Radiated hash is picked up by the braid but is not
> picked up by
> the inner. Therefore, hash voltage exists between braid and inner. This
> hash voltage is
> carried straight into the receiver!
>
> Twisted balanced feed such as 300 ohm TV ribbon picks up hash equally on
> both wires
> so they cancel each other. This ribbon has negligible loss at 80m
> and will scarcely add
> any additional loss when the SWR is very high, as with a very short dipole
> near ground
> level.
>
> 73 de Neil ZL1ANM
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