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Re: [RFI] RFI from satellite modem

To: rfi@contesting.com
Subject: Re: [RFI] RFI from satellite modem
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Tue, 21 Dec 2010 23:00:40 -0800
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 12/21/2010 9:16 PM, AE5B wrote:
> Any ideas as to where I should start.

Study http://audiosystemsgroup.com/RFI-Ham.pdf

The executive summary is that one or more of the wires is acting as a 
long wire antenna, radiating trash generated in the electronics and in 
the power supplies for the electronics. The first line of attack is a 
common mode choke on each of those wires, each choke wound so that it's 
tuned for the frequencies where you hear the noise.

Study the text that talks about ferrite chokes, then the part that 
addresses killing RFI in Ethernet gear and CATV systems, then use the 
curves (measured data) in Appendix One as a guide when winding the 
chokes. For 30-160M, you should probably start with 14 turns around a 
2.4-inch #31 core.  Apply chokes to each power cable, and to each cable 
that is connected to the various boxes.

Another good move that W9AC has discussed here is to replace the wall 
warts, which are probably switching power supplies, with linear 
supplies. This eliminates the part of the trash generated by these 
supplies, leaving you with only that generated by the electronics itself.

You DO want everything properly grounded, so I would definitely call the 
Wild Blue folks and tell them to get a grown up there to do it right.  
You paid for it.  And I would also tell them to get rid of the RF trash.

Another common coupling mechanism is poorly crimped cable shields.  
Again, that's THEIR job, and it's tough to do without the right size 
F-connector for THAT size of cable, and a proper crimp tool.

Finally, SOME RF can be radiated directly by the wiring inside equipment 
that is poorly shielded, or has poor circuit board layouts, or both.  
Nothing is going to fix that short of shielding it, which can be a real 
science project. :)  Again, the best move is to call Wild Blue and tell 
them to fix it.

73, Jim Brown K9YC

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