Mark Levinson 380 Owner's Manual page 38

Ground Isolation Adaptor
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place in-line with your cable feed, prior to the system connection
The assembly shown above may cause some loss of video signal
strength and/or bandwidth, and should be used as a temporary fix. It is
useful in determining the cause of some video-related noise problems,
however, and costs only a few dollars. If it seems to correct a problem,
consult with your dealer regarding a long-term solution which does
not degrade video performance.
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