[TowerTalk] Mains Filter for 80M

Jim Hargrave w5ifp at gvtc.com
Fri Jun 8 11:10:33 PDT 2012

The Isobar filter that I have has individual Toroid filters on each line
inside the metal box. Additional Toriod filters are between the stage 1 and
stage 2 outlets. Both the hot and common lines are individually filtered.
Even though it contains MOVs, It is not mill-of-the-run MOV surge protected
power strip. Hence the additional costs.

A brief description of the four outlet unit is at:


Disclaimer: I have no interest in Tripplite...just a satisfied user. Works
for me.

    73s de Jim

  > -----Original Message-----
  > From: towertalk-bounces at contesting.com
  > [mailto:towertalk-bounces at contesting.com]On Behalf Of Jim Brown
  > Sent: Friday, June 08, 2012 11:08 AM
  > To: towertalk at contesting.com
  > Subject: Re: [TowerTalk] Mains Filter for 80M
  > On 6/8/2012 8:41 AM, Jim Hargrave wrote:
  > > I use an ISOBAR IB-4 dual stage line filter.
  > > It is a combination noise and surge protector.
  > Remember that shunt mode surge protectors (MOVs) are safe ONLY at the
  > building service entrance (so-called "whole house" suppressors). When
  > installed on branch circuits at at outlets, they are as likely to CAUSE
  > equipment failure as to prevent it.
  > I've put several RF line filters that "look good on paper" into
  > enclosures and wired to connectors for use on Field Day and Califorrnia
  > QSO Party county expeditions to clean up noisy generators.  They have
  > been totally ineffective for common mode noise, and the noise most
  > likely to cause us trouble is common mode noise.  What DOES work for
  > common mode noise is to wind turns of the power cord through a suitable
  > ferrite core. 12-14 turns through a #31 toroid would be just about
  > optimum for 160-40M.  6-8 turns would be about right for the higher HF
  > bands.  A #43 core needs at least 14 turns for 80M, and works
  > as well as
  > #31 for the higher bands.
  > What is equally important is proper bonding of all grounds and systems
  > in your home and shack.  That means bonding the power system ground to
  > your shack ground, cable TV, satellite, telephone, etc.  AND it
  > can also
  > help to use ferrite chokes on the Beverage coax, and any nearby wiring
  > that can radiate noise into your antennas, including the Beverage.
  > 73, Jim Brown K9YC
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