[RFI] Computer Hash

Jim Brown jim at audiosystemsgroup.com
Mon Feb 26 02:20:14 EST 2007

On Sun, 25 Feb 2007 22:32:55 -0000, William Conlan wrote:

>Hi Guys, anyone have a fix for stopping computer noise blocking 
>HF Radio. 
>I use 3.5" Jack lead into PC microphone  & 3.5" Jack into radio
>speaker source on radio.

>As soon as I switch on computer all I get is noise.
>This is not a problem on VHF only HF 2Mgh-30Mgh.

Take a look at the RFI tutorial on my website.


Some questions:

1) Does the noise go away (or get weaker) if you disconnect some 
or all of the wires plugged into the computer?  If the answer is 
yes, those wires are acting as antennas, radiating the noise that 
is most likely being put on them by pin 1 problems inside the 
computer. Common mode chokes will help that part of the problem. 
Follow the instructions in my tutorial. 

2) Does some of the noise persist when all the wires are 
disconnected?  If the answer is yes, that part of the noise is 
probably being radiated directly by wiring inside the computer(s) 
because they are not adequately shielded. Either you shield them 
(a lot or work) or use the bucket treatment. See the tutorial for 

For both of these questions, consider ALL of the wires, even the 
power supply for the laptop. (Obviously the non-laptop won't work 
without power). 


Jim K9YC

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