[TenTec] installing ladder line

[Paul Christensen]

> Ladderline behaves differently from coax, and there might be a small
> impedance "bump" if you turn it abruptly through 90 degrees; however, in
> many ladderline applications that wont matter.

Good advice Steve.  A transmission line impedance "bump" is generally only 
an issue when the line must be terminated into its characteristic impedance. 
In that case, the impedance on the line as a function of distance from the 
load does not change.

When open wire line is terminated into a mutiband dipole: (1) the antenna 
terminal impedance radically changes across bands of operation, antenna 
length, and antenna height; (2) the impedance at every point along the open 
transmission line is changing, typically in great variation, depending on 
the mismatch magnitude between the antenna terminals and the characteristic 
impedance of the line; and (3) the SWR on any line segment stays constant, 
notwithstanding line loss:  For example, if multiple line types are used 
between an antenna and transmitter, each line with a different 
characteristic impedance (e.g.,600 ohm from the antenna for some distance, 
then 50-ohm from the transition back to the rig), the SWR at all points on 
the 600-ohm segment remain the same but the SWR on the 50-ohm segment is a 
different value, but also constant at any point on that line segment, 
neglecting line loss.  By changing the length of the 600-ohm line, it's 
often possible to attain a resistive 50-ohm impedance at the end of the 
600-ohm line section, perfect for terminating into 50-ohm coax f any length.

So, unless an open, balanced line is always operating into its 
characteristic impedance, the bumps do not matter.

Paul, W9AC