Topband: Filters and grounding

[Tom Rauch]

> That is the "old" way. Bill Whitlock published an AES 
> paper (JAES
> Jun 1995) that convinced everyone who read it that the 
> proper
> shield connection for a "one end only" bond is at the 
> SENDING end,
> not the receiving end.

Since the input of a device is almost always more sensitive 
to RFI than the output, I'm not convinced his way is 
correct.

But the most important thing is to not have a power line or 
audio frequency "ground loop" on the shield, since it is mch 
thinner than the skin depth and does not behave like a 
traditional shield on our RF cables.

> However, BALANCED shielded cables are VERY different from 
> coax
> with respect to the behavior of the shield. With balanced 
> cables,
> the shield is effective only against the electric field, 
> NOT a
> magnetic field.

That is only true because the shield is not several skin 
depths thick at audio.

> With coax, the shield is not really a shield, it
> is one conductor of a transmission line, and the rejection 
> of
> external fields comes from the mutual coupling between the
> "shield" and the center conductor

That is true at audio, where it is not practical to have a 
shield thick enough to be several skin depths thick.
That is not true at radio frequencies, where the shield is 
many skin depths thick.

> The primary reason that balanced audio cable shields must 
> be
> opened at one end is THE PIN 1 PROBLEM.

The ground loop is the pin one problem. This however is out 
of the scope of anything useful to 160 meter hams except for 
audio lines.

The topic here is RF lines and RF suppression of RF signals, 
frequencies that should NEVER be mixed in with behavior of 
audio lines where the skin depth cannot offer isolation 
between the inner and outer walls. I'm afraid mixing that in 
will only confuse people into thinking RF fields and lines 
behave like audio lines.

73 Tom