[TowerTalk] Mains Filter for 80M

Jim Brown jim at audiosystemsgroup.com
Fri Jun 8 09:07:43 PDT 2012

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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