Topband: Antenna question
w8ji at w8ji.com
Mon Mar 31 10:55:41 EDT 2014
> 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
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
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