[TowerTalk] Mains Filter for 80M

Jim Lux jimlux at earthlink.net
Fri Jun 8 13:37:57 PDT 2012

On 6/8/12 9:07 AM, Jim Brown wrote:
> 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.


That's what's worked the best for me.. Noisy wall warts and such.. they 
propagate the noise back into the house wiring.  I just have a bunch of 
short 6' extension cords and a box full of #31 cores.

A lot of people have problems with Cat5 network wiring, but so far, I've 
had relatively little problem from that.

Now, there is a nasty birdie in the middle of 20m from my car (even when 
the key is off)... But short of building a faraday cage for the car, I 
just have to live with it and hope it drifts into places I don't use.

More information about the TowerTalk mailing list