[RFI] 160M Interference from Mac G4 Monitor

Jim Brown jim at audiosystemsgroup.com
Tue Dec 22 10:01:06 PST 2009

On Tue, 22 Dec 2009 10:36:07 -0600, K4RO Kirk Pickering wrote:

>I need to find a solution where the YL can work on her Mac while I
>comb through the static on 160m. 

Hi Kirk,

To kill it, you need to understand how it is getting to you. There 
are two most likely mechanisms. One is easily fixable, the other is 
not. The fixable one is also the most likely on 160M -- radiation 
from wiring external to the monitor. In this scenario, that wiring 
is acting like a long wire antenna, so the way to kill it is to 
choke it. See my RFI tutorial for specific directions on how to wind 
ferrite chokes to kill it. You will need ferrite cores made of Fair-
Rite #31 material to make a dent in 160M trash. 


Every wire connected to the the noise source is a potential antenna, 
but begin with the longest wires, because they are the most 
efficient antennas on 160M. I'd start with the power supply cables 
and the cable between the monitor and the computer. BTW -- power 
supplies are a major source of noises like this. They are 
essentially oscillators (mostly for switching power supplies) that 
are dithered so that their trash is spread out over a wider 
bandwidth so that it does not exceed FCC or EU limits. 

The other mechanism? Direct radiation from wiring (antennas) inside 
the monitor or computer radiating the trash. In other words, lousy 
shielding. This is much less likely unless the monitor is very close 
to your RX antenna(s) because the internal antennas are much 
shorter. That requires my "bucket treatment." Find a bucket big 
enough to hold the monitor, fill it with water, put the monitor in 
the bucket twice. Take it out once.


Jim K9YC

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