Topband: QST Jun 06 RX Loop

[Tom Rauch]

> Tom is confusing Faraday shield with Electrostatic shield 
> and whole reasoning that the grounded shield of small loop 
> antenna is THE antenna is all wrong. Wire loops inside the 
> electrostatic shield are perfectly OK to receive the RF 
> and ARE the antenna.

It's a very well known property that nothing passes through 
the walls of a shield more than several skin depths thick. 
This is because skin effect keeps the current in the outside 
layers and the core of the shield wall is dead. This is the 
very thing that allows our coaxial lines to behave like 
three conductors, a center conductor, a inner wall, and an 
outer conductor. The physical behavior of a shield does not 
change with application.


>Electrostatic shield in small loop antennas reduces the 
>interference, electrical noise locally generated (prevalent 
>electrical fields).

Not so Yuri.

First an electrostatic field by definition is a non-changing 
field. Static is stationary or unchanging, and things that 
aren't changing can't make RF noise.

The field from an accidental transmitter (noise source) is 
just like the field from any intentional signal source like 
a transmitter. There is absolutely nothing that says the 
field has a high field impedance (electric field dominant). 
Even if it was a high impedance at the source, just 1/10th 
wave or so from the source the field  would change to a low 
impedance.

We can't filter noise by virtue of field impedance or a 
shield. Even if we could, the noise source in the nearfield 
would randomly field dominant depending on distance and 
source charateristics.

The only thing the shield can do at radio frequencies is 
change the system balance.

73 Tom