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Re: [RFI] 6M Getting into TV Channel 3 - CLARIFIED!

To: "RFI List" <rfi@contesting.com>
Subject: Re: [RFI] 6M Getting into TV Channel 3 - CLARIFIED!
From: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Thu, 03 Jul 2008 09:50:25 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
I'd say common mode and differential mode are equally likely. A ferrite choke 
on the coax is the right fix for common mode. A bandpass filter (or bandstop 
filter) is the right fix for differential mode. The transformer someone 
mentioned is NOT likely to be a good fix. 

See my RFI tutorial for specific recommendations for a ferrite choke for 6M. 
Use the graphs of choking impedance to obtain at least 1,000 ohms at 50 MHz. 
Depending on the severity of the interference, a higher impedance may be 
required. You need to put the choke right in front of the gear that is letting 
the RF into the system. That MIGHT be the distro amp, or it might be the TV 
set, or it might be something else around the TV set.  

Also study the material in my tutorial about "the pin 1 problem." It is the 
MOST common coupling mechanism for RFI. 


The FILTER should go in front of the distro amp. Tin Lee Electronics, near 
Toronto, is a good source of filters. I used two of their filters when I lived 
in Chicago. They worked. I also had ferrite chokes on the cables. 

One easy way to check for common mode or differential mode is to connect ONLY 
the shield of the coax to the distro amp and see if you have the RFI. If you 
do, it's common mode. If you don't, it's differential. It's also possible that 
you have both differential and common mode coupling. 


Jim K9YC

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