Topband: Cone of Silence

[Tom Rauch]

> I sure enjoy the discussion on this topic. However,  I would like to
> sheepishly, perhaps foolishly, ask if folding the short vertical
> Beverage termination down lead wire back and forth on itself with some
> small spacers would reduce the vertical pick up somewhat due to a
> cancellation effect.?

Unfortunately it cannot do anything except add some small amount of
additional loss resistance. If it did, or if you find a way to do that, let
me know. We can be rich becuase we will solve all types of problems!

> Another means, although more complex, might be to mount the termination
> resister at the high point and construction the earthing wire out of
> Tri-Ax forming a Faraday shield.  The  Faraday shield principles work
> well at AF and Video mitigating induced hum in long runs of cable.

Won't work just like shielding a loop doesn't work. Faraday requires a
closed volume of space with no conductors extending outside and no gaps.

The second you put a gap there, you allow voltages appearing across the
outside length of the shield to drive the impedance of the inner wall, and
the system acts just like the screen isn't there. The only thing the shield
does in a loop or in the audio cables is preserve balance if the system is
properly built.

In a piece of coaxial cable, if you don't terminate the far end, you won't
have signal pickup. But that's because the center conductor and shield have
parallel voltages and currents. If you leave the shield loose at one end and
ground the center (or connect the center to anything with a low impedance)
it acts like the shield isn't there!

There isn't any way around this problem Herb. The only thing that happens by
putting an open ended shield over a cable is the common mode currents move
over the outside of the shield and spill right back over to the inside.

If there was a way around that Faraday and Maxwell would be wrong and we
could sell 100 ft long ground leads that wouldn't have high impedance or
radiate on ten meters!

73 Tom