[RFI] Stereo/audio EMC question

Jim Jarvis jimjarvis at verizon.net
Sun Nov 27 13:19:18 EST 2005


I have an idea how I want to handle this situation, but
would like to get the benefit of others thinking, in advance.

First, no station is up, as yet.  Should have a 706-II & an
R7000 vertical operative by Christmas.   Eventually, I'll be
back at a kw, with steppIR & lowband wires.  For purposes of
this discussion, assume good grounds at tower and buried radials
for all verticals...and all coax and control lines run via conduit
to a central ground point, before entry to basement.

Now comes the question:

I have a sound system which poses the potential for RFI pickup,
and would like the benefit of your thinking.

It's an ONKYO modular system, with metal cabinets, and properly
bared points such that each module is shielded.  It's proven 
bulletproof with no special treatment, using the tuner, CD and
tape drives in the system.  Even with dual speaker systems, one of
which ran 100' or more, and through the ham shack.

Here's the change:  I'm dubbing all CD's into iTunes in a mac-mini,
and feeding the stereo via a line input (vcr-2) from a 16 ohm phone/
speaker line out of the mac-mini.  The computer, in turn, is connected
to my router.  The benefit of this is that iTunes goes to a web database
and imports the names and detail for all CD tracks.  I am concerned about
ground loop pickup of RF.  One option is to install the airport card into
the mac-mini, to break that loop.  

The other detail is that I'm again running B speakers, although this time
a distance of maybe 50'.  

There is no way to avoid being in the near field of any of the antennas.
It's a 1/3 acre suburban lot.  

My tentative plan is to isolate the data link via wifi, and liberally apply
ferrites to the speaker lines, or to the computer/input side, 
if anything crops up.

Anybody see a flaw in my thinking, or something I've overlooked?

jimjarvis at ieee.org 

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