Madrigal Imaging N38 - Manual (Page 30)

30
In some cases, connecting your audio and video systems together in
this fashion can result in noise, typically a 60 Hz or 120 Hz hum. The
most common cause for this noise is a “ground loop” caused by the
presence of two ground references in the system: one from the power
company and another from the cable-television company. The
simplest way of solving this problem is to break the cable company’s
ground by using an isolation transformer on the incoming cable line,
before it reaches your television or VCR. If you cannot find a 75
Ω
-75
Ω
balans (isolation) transformer, you can easily construct one from the
adaptors which probably came with your VCR and television, as
shown below.
75
Ω
300
Ω
300
Ω
75
Ω
Ground Isolation Adaptor
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. If it seems to correct a problem, consult with your
dealer regarding a long-term solution which does not degrade video
performance.
Ground Isolation Adaptor
Noise in A/V systems