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Re: Topband: Coax Shield vs. Ground & elevated radials

To: Björn Mohr <bm@broadcast.se>,<topband@contesting.com>
Subject: Re: Topband: Coax Shield vs. Ground & elevated radials
From: "Tom Rauch" <w8ji@contesting.com>
Reply-to: Tom Rauch <w8ji@contesting.com>
Date: Tue, 2 Jan 2007 12:46:32 -0500
List-post: <mailto:topband@contesting.com>
Update: I added the choke at the antenna base. Before doing 
that I created a
probe by wounding abt 15 turns of enamelled wire around the 
coax close and
localised a point on the coax with a maximum reading close 
to the shack>>

The magnetic field from common mode currents is in the form 
of rings around the coax. Consider the coax an axle or axis, 
the magnetic field would be a ring.

As a consequence your winding would have to be a small 
spiral circling the circumference of the coax. You could not 
wind it directly around the coax like the coax is a core or 
you would not read what you think you are reading.

This is why the only reliable method that works is a 
soft-iron core that circles the entire coax and you wind a 
small winding on that core.

See:

http://www.w8ji.com/building_a_current_meter.htm

73 Tom



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