[RFI] Ladder Line and RFI/Noise

[Paul Christensen]

> Thanks Jim. In my case I'm 1000 feet from the nearest neighbors, so my
> ladder-line fed dipole isn't an issue in that regard.

The issue for most of us is not limited to our neighbors, but our own 
home-grown noise sources.  I agree with Jim.  Parallel tuned feeders can be 
susceptible to nearby noise sources.   The problem become more prevalent 
with the wider-spaced lines.  I use 600-ohm line with a very wide conductor 
spacing.  That has caused me to dig pretty deep into RFI mitigation around 
my home as well as the neighbors around me.  Despite the pain in dealing 
with the noise, it's been a worthwhile effort, especially since I can tune 
anywhere from 160m through 10m using a motorized high-power ATU outside the 
shack with about 100 feet of tuned feeders.

As line spacing narrows, line loss increases, but immunity improves.  A long 
time ago E.F. Johnson sold "transposition" line blocks to help with the 
noise issue.  Back then, switch-mode sources did not exists, but motor brush 
forms of interference has been with us since the time of Marconi.  I have no 
idea as to the effectiveness of the blocks.  The blocks are placed on the 
line every 1-2 feet to form a continuous, moderate twist.  The blocks are 
made of glazed ceramic and really add to the line weight.

Anyone have experience with the transposition blocks?

Paul, W9AC