[ARC5] BC-230 mic

[hwhall at compuserve.com]

>
hash voltage exists between braid and inner. This
hash voltage is carried straight into the receiver!
>

 It's normal for different RF currents to be able to flow on the outer and inner surfaces of properly assembled coax. That's why it's good practice to connect coax cable braid to the chassis as it enters an RF tight chassis -- to keep any currents on the outside of the coax only on the outside the chassis.


Wayne
WB4OGM

 

-----Original Message-----
From: AKLDGUY . <neilb0627 at gmail.com>
To: Jim Wiley <jwiley at gci.net>; ARC-5 List <arc5 at mailman.qth.net>
Sent: Mon, Nov 10, 2014 4:50 am
Subject: Re: [ARC5] BC-230 mic


> 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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