Topband: Antenna question

[Tom W8JI]

> I agree with everything Tom has stated here, with one MAJOR exception. The 
> generic audio "rack cable" that is twisted pair with a foil shield and 
> drain wire as made by Belden and everyone alse is a TRAIN WRECK for RF 
> intrusion from the shield to the pairs. The drain wire is the bad guy --  
> no problem with braid shields, with or without foil.

Actually, none of that matters in a Beverage application with proper 
transformer designs. It doesn't matter if the shield is there or not, or if 
the wires are twisted or parallel, if the transformers are properly made and 
connected.

Instability in the line caused by things like standing water trapped between 
the pair would affect line impedance and transmission loss. This could hurt 
wet weather performance. Of course loss would also affect signal levels from 
the far end but even that doesn't normally mean much. Beverages have a great 
deal of signal level head room.

I think the real problem here is some past articles have made some pretty 
silly statements about wire position "shielding" the antenna from signal, 
reducing signal pickup. This misconception makes some of cautious about wire 
positions and types.

It really doesn't matter one bit for signal reception. In common mode (for 
signal reception in either direction), any shield quality or wire twist is 
meaningless. The impedance between wires is meaningless, and the loss is 
meaningless for signal pickup.

It is only in the conveying of signal to and from the far end as a 
transmission line that loss and impedance has any effect on the system. Even 
in this case, shield performance and wire lay is meaningless with properly 
constructed transformers. It doesn't matter if the shield is there or not, 
and it doesn't matter if the wires are twisted or not, so long as it 
functions as a stable impedance line with reasonable spacing and acceptable 
losses.

73 Tom