Topband: Common-mode noise/long buried feedline runs

[Mike Bragassa]

TB-er's:
OK; best to suppress common-mode at the feed-point; agree.
What about long feedline runs...buried? My 80 , 160 xmit antenna's and 
Beverages each have at least 300 foot coaxial feedline runs, buried about an 
inch below ground. Should I ...also.... suppress at the shack end and in 
what recommended manner?

Tks, Mike K5UO
...............................................................<>..............................................................
" "From: "Guy Olinger, K2AV" <olinger at bellsouth.net>
Subject: Re: Topband: Coax Shield vs. Ground & elevated radials
....//.....A fuzzy general rule is: a common mode suppression device does 
best if
placed at a point which would otherwise be a common mode current
maximum.

It can be tricky KNOWING where the pre-suppression common mode current
maxima ACTUALLY lie. There are no utterly dependable simple rules for
locating them, other than MEASURING them. Various posted/published
"rules" that DO work are HIGHLY SITUATIONAL. They simply may not work
if attempted in different circumstances. When reading anecdotal or
technical descriptions of successful suppressions **pay close
attention to the details**.

Placing a single suppression device may simply MOVE common mode
current maxima without much reduction of loss on transmission or
common mode noise pickup. A pair of suppressors spaced roughly 1/4
physical wavelength may work where one did not. This is particularly
true if some part of the system is grounded at the antenna or between
the antenna and the suppression.

Be prepared to redo antenna matching after successful common mode
suppression. It is easy to create a model with more common mode
current on the feedline than desired current on the antenna....//........""